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Caloric expenditure and substrate utilization in underwater treadmill running versus land-based treadmill running
h [electronic resource] /
by Courtney Schaal.
[Tampa, Fla] :
b University of South Florida,
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Thesis (M.A.)--University of South Florida, 2009.
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Text (Electronic thesis) in PDF format.
ABSTRACT: The objective of this study is to compare the caloric expenditure and oxidative sources of underwater treadmill running and land-based treadmill running at maximal and submaximal levels. Underwater running has emerged as a low load bearing form of supplementary training for cardiovascular fitness, as a way to promote recovery from strenuous exercise while maintaining aerobic fitness, and as a way to prevent injury. Prior studies have reported conflicting results as to whether underwater treadmill running elicits similar cardiorespiratory responses to land-based running. It is important to further investigate the similarities and differences between the two to determine if underwater running is as efficient as land-based running for maintenance of fitness and for rehabilitative purposes.Purpose: To compare the caloric expenditure and oxidative sources of underwater treadmill running and land treadmill running during both maximal treadmill trials to exhaustion and during 30 minute submaximal treadmill trials. Methods: 11 volunteer experienced male triathletes, ages 18-45 were recruited as participants. Each completed 6 trials total which included a maximal and submaximal oxygen consumption trial for each of three conditions: running on a water treadmill with AQx water running shoes, running on a water treadmill without shoes, and running on a land-based treadmill. Data analysis: Data was analyzed using repeated measures ANOVAs, paired t-tests, pairwise comparisons with bonferroni adjustments, and descriptive statistics were reported. Results: For maximal oxygen consumption trials VO, RPE, RER, and BP were not significantly different between modalities.Maximal HR was found to be significantly different between modalities, and was shown to be greater on land than in the water. For submaximal VO, trials HR, RPE, RER, and post BP were not found to be significantly different between modalities. Average VO,, total calories expended, and pre systolic BP were found to be significantly different, and were shown to be greater on land than in water. Conclusions: While maximal exertion running on underwater treadmills seems to elicit similar cardiorespiratory responses to running on land-based treadmills, differences were seen at submaximal exertion levels. It remains unclear whether underwater treadmill running can elicit similar training stimuli as land running at submaximal levels.
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Advisor: Candi Ashley, Ph.D.
x Physical Education and Exercise Science
t USF Electronic Theses and Dissertations.
Caloric Expenditure and Substrate Utiliza tion in Underwater Treadmill Running Versus Land-Based Treadmill Running by Courtney Schaal A thesis submitted in partial fulfillment of the requirements for the degree of Master of Arts Department of Physical Edu cation and Exercise Science College of Education University of South Florida Major Professor: Candi Ashley, Ph.D. Bill Campbell, Ph.D. Robert Dedrick, Ph.D. Marcus Kilpatrick, Ph.D. Date of Approval: July 2, 2009 Keywords: underwater running, aquatic tr eadmill, caloric expenditure, substrate oxidation, RER Copyright 2009, Courtney Schaal
Table of Contents List of Tables ii List of Figures iii Abstract iv Chapter One Introduction Rationale 1 Background 2 Hypotheses 4 Chapter Two Review of the Literature 5 Chapter Three Methods Participants 14 Experimental Design 15 Protocol 16 Maximal Tests 18 Submaximal Tests 21 Measures 22 Statistical Analysis 25 Chapter Four Results 26 Test of Hypotheses 28 Contributing Variables 30 Chapter Five Discussion 36 References 45
ii List of Tables Table 1 Participant Demographics (n=10) 15 Table 2 Trial Conditions Completed by Each Pa rticipant 17 Table 3 Maximal VO2 Trial Protocols 20 Table 4 Submaximal VO2 Trial Values 22 Table 5 Maximal Test Results 27 Table 6 Submaximal Test Results 27 Table 7 Caloric Expenditure (main effects) 28 Table 8 Caloric Expenditure (pairwise comparisons) 29 Table 9 Substrate Utilization (at subm aximal levels) 29 Table 10 Pairwise Comparisons for Variab les of Significance 30
iii List of Figures Figure 1 Results of Maximal Oxygen Consumption Trials 33 Figure 2 Results of Submaximal Oxygen Consumption Trials 34 Figure 3 Submaximal Calori es and Substrates Utilized 35
iv Caloric Expenditure and Substrate Utiliza tion in Underwater Treadmill Running Versus Land-Based Treadmill Running Courtney M. Schaal ABSTRACT The objective of this study is to comp are the caloric expenditure and oxidative sources of underwater treadmill running and land-based treadmill running at maximal and submaximal levels. Underwater running has emerged as a low load bearing form of supplementary training for cardiovascular fitn ess, as a way to promote recovery from strenuous exercise while maintaining aerobic fitn ess, and as a way to prevent injury. Prior studies have reported conflicting results as to whether underwater treadmill running elicits similar cardiorespiratory responses to land-based running. It is important to further investigate the similarities and differences between the two to determine if underwater running is as efficient as land-based running for maintenance of fitness and for rehabilitative purposes. Purpose: To comp are the caloric expenditure and oxidative sources of underwater treadmill running and land treadmill running during both maximal treadmill trials to exhaustion and during 30 minute submaximal treadmill trials. Methods: 11 volunteer experienced male tria thletes, ages 18-45 were recr uited as participants. Each completed 6 trials total which included a maximal and submaximal oxygen consumption trial for each of three conditions: running on a water treadmill with AQx water running shoes, running on a water treadmill without shoes, and running on a land-based treadmill.
v Data analysis: Data was analyzed using re peated measures ANOVAs, paired t-tests, pairwise comparisons with bonferroni adjustments, and descriptive statistics were reported. Results: For maximal oxygen consumption trials VO2, RPE, RER, and BP were not significantly different between modalities. Maximal HR was found to be significantly different between modalities, and was shown to be greater on land than in the water. For submaximal VO2 trials HR, RPE, RER, and post BP were not found to be significantly different between modalities. Average VO2, total calories expended, and pre systolic BP were found to be significantly different, and were shown to be greater on land than in water. Conclusions: While maximal exertion running on underwater treadmills seems to elicit similar cardiorespiratory responses to running on land-based treadmills, differences were seen at submaximal exertion levels. It remains unclear whether underwater treadmill running can elicit similar training stimuli as land running at submaximal levels.
1 Chapter One Introduction Rationale The purpose of the present study was to investigate the caloric expenditure and oxidative sources for underwater treadmill r unning in comparison to land-based treadmill running, at both maximal and submaximal exer tions. Underwater running has emerged as a low loadbearing form of supplementary traini ng for cardiovascular fitness, as a way to promote recovery from strenuous exercise wh ile maintaining aerobic fitness, and as a way to prevent injuries (Reilly & Dowzer, 2003). It provides a method of decreasing the running impact forces and the negative eff ects of excessive mileage when used in supplement to a runners regular training program, while at the same time maintaining a training stimulus. Underwater running has been reported to reduce spinal and joint compressive loading which decreases th e likelihood of incurring running-related musculoskeletal injuries, especially overuse injuries such as plan tar fascitis, tendonitis, and stress fractures (Silvers, Rutledge, & Do lny, 2007). It has traditionally been used for aerobic conditioning during rehabilitation, but whether it elicits a cardiovascular and metabolic training stimulus comparable to that of land-based running is seemingly unclear. Previous literature has reported conf licting results possibly due to differences in the nature and protocol of each study, met hods used to run under water, and training status and running style of the participants. This study aims to further investigate whether
2 underwater treadmill running elicits similar car diorespiratory and metabolic responses to land-based treadmill running, specifically in terms of caloric expe nditure and substrate utilization (in percen tage of fats and carbohydrates utilized). Background In the past underwater running has been performed primarily through deep water running (DWR) utilizing a buoyancy device to run in the deep end of a pool. This method of underwater running allows th e athlete to reproduce the pa ttern of limb movement used during land-based running, without the ground support phase which eliminates the impact. Silvers et al. (2007) states that while this is the most comm on form of underwater running used in the past, DWR has been shown to be quite different from land-based running pertaining to muscle recruitment and kinema tics of the lower extremities. Another form of underwater running that has emerged to more closely mimic land-based running is shallow water running (SWR), where the indivi dual will run in the shallow end of a swimming pool, typically at a waist deep water level. SWR adds a ground reaction force component while still allowing for reduced impact. If the water level during SWR is raised it increases the amount of water resistance, therefor e presumably increasing the cardiorespiratory demand for a given worklo ad, but at the same time increasing the frontal resistance of forward movement in water which may degrade overall running mechanics (Silvers et al., 2007). With DWR a nd SWR posing certain limitations in their ability to resemble land-based running, unde rwater treadmills have more recently emerged. Underwater treadmills eliminate forward movement and therefore resistance through water allowing for a more natural gait pattern, and incorporate a reduced impact
3 ground support phase which may enhance the sp ecificity of underwat er training (Silvers et al., 2007). With this being possible, underwater running should more effectively produce metabolic responses similar to those seen during land-based running. Previous literature has investigated whether underw ater running actually does elicit similar metabolic responses to those seen on land in order to provide a foundation for the value and effectiveness of underwater running as a training modality. In recent years, AQx Sports Deep Water Running shoes have been designed specifically to enhance deep water running. They are desi gned to simulate running on land without the associated impact of running on land, and are thought to be more similar to land-based running than running in the wate r barefoot. There is an added weight when wearing the shoes, and they also have gil ls on the sides, which create additional water resistance. The additional grip on the bottom of the shoes allows for greater traction when running on the bottom of the pool, which in turn allows for a larger range of motion that more closely resembles running on land. Research performed by the makers of AQx shoes during deep water running found that us ing the shoe enhanced the participants kinesthetic perception and allowed the deep water gait pattern to be more similar to landbased running and walking. However, research has not been conducted to evaluate the physiological effects of the use of the AQx shoes during underwater treadmill walking or running. If these shoes allow for deep water r unning that is more similar to land-based running, it seems logical to assume that the physiological advantages of the shoes used would also be found to be enhanced with use of an underwater treadmill. Further establishing (or refuting) the effectiveness of AQx water running shoes as a mechanism to enhance running on an underwater treadmill will lend additional research to what is
4 already known regarding both water treadmill running in general as well as water treadmill running utilizing these shoes. Hypotheses: Null hypotheses (Ho): ( Ho1) : There is no significant difference in the caloric expenditure during underwater treadmill running (with or without AQx water running shoes) compared to land-based treadmill running at submaximal exercise intensities equivalent to 70 percent of maximum VO2. ( Ho2) : There is no significant difference in the s ubstrate utilization (percent of fats and carbohydrates utilized as determined by RER) during underwater treadmill running (with or without AQx water running shoes) compared to land-based treadmill running at submaximal exercise intensities equi valent to 70 percent of maximum VO2. Alternative hypotheses (Ha): (Ha1): Underwater treadmill running (with or without AQx water running shoes) will elicit a greater caloric expenditure than land-based treadmill running at the same submaximal exercise intensities equi valent to 70 percent of maximum VO2. (Ha2): Underwater treadmill r unning (with or withour AQX water running shoes) will have a greater utilization of calories fr om carbohydrates than land-based treadmill running at submaximal exercise intensities equivalent to 70 percent of maximum VO2.
5 Chapter Two Review of the Literature It is important to consider the hydros tatic effect associat ed with underwater running which in itself causes cardiorespir atory adjustments prior to discussing what previous literature has re ported in terms of underwater running and its effect on metabolic responses. Upon immersion in wate r a hydrostatic vascular gradient occurs causing a shift in blood volume compartments, which when combined with the adjusted intra-thoracic pressures rela tive to the surrounding water pressure, contributes to an increased central blood volume as peripheral blood volume is displa ced to the central core (Reilly et al., 2003). Much of the cardior espiratory changes that occur in water are due to the extra pressure placed on the thorac ic cavity and abdomen affecting the heart and the lungs. Due to the increased centra l blood volume, there is also an enhanced diastolic filling which leads to an elevated stroke volume, and in turn an increase in cardiac output (Arborelius, Balldin, Lilja, & Lindgren, 1972). The increased arterial pressure induced from the hydrostatic effect of water causes a rise in heart rate (HR), as well as stroke volume (Farhi & Linnarsson, 1997). Lung function is hindered by the pressure that water places on the body, c ounteracting inspiratory muscle function by compressing the abdomen and raising the diaphragm to near full expiration. This reduces lung and vital capacities, leading to an increased breathing frequency and rate, and therefore higher minute ventilation (Ve) to produce oxygen consumption (VO2)
6 equivalent to that of exercise on land (Rei lly et al., 2003). With the combination of an increased central blood volume and reduced insp iratory force there is a noted decrease in functional residual capacity and expiratory reserve volume (Reilly et al., 2003). With these changes associated with the hydros tatic effect of wate r encountered during underwater running, you would expect the metabolic responses during DWR, SWR, and underwater treadmill running to vary from those seen during land-based running. The majority of the previous literature has invest igated this through th e utilization of DWR. Fewer studies have investigated metabolic responses to SWR and underwater treadmill running, as they are newer means to perfor m underwater running (Dowzer et al., 1999, Pohl & McNaughton, 2003, Silvers et al., 2007). In this review of the literature all three types of underwater running will be discussed. Previous literature has produced mixed re sults regarding the ca rdiorespiratory and metabolic responses to underwater running. This could be due to th e type of protocol used, the training level of the participants, wh at in specific is bei ng investigated, and the variations seen among the different types of underwater runni ng (such as DWR, SWR, or running on underwater treadmills). The majority of prior studies ut ilizing buoyancy vests in pool running seem to have noted a decrease in maximal VO2 as well as a decrease in HR. Butts, Tucker, & Greening (1991) conduc ted a study to investigate the maximal physiological responses to treadmill running on land and deep water running using a flotation device. The participants incl uded 12 trained men and 12 trained women. Maximal aerobic capacity (VO2 max), HR, and respiratory exchange ratio (RER) were measured. While men elicited slightly higher maximal VO2 capacities than women and were similar across all other variables, bot h genders demonstrated significantly lower
7 maximal VO2 capacities and HR during underwater r unning in comparison to land-based treadmill running. The RER did not vary signif icantly in either gender between modes. This studys findings were supported by a nother study done by Frangolias & Rhodes (1995). This study compared the metabolic responses of treadmill running and water immersion running using a buoyancy device. Participants included 13 trained male endurance runners who were familiar with non-weight bearing water immersion running. Each participant completed tests at ventilator y threshold as well as at maximal intensity, both on land and during water immersion. VO2 max, HR max, RER, VO2 at ventilatory threshold, and HR at ventilatory threshold were all reported to be lower during water immersion running. With a decrease in VO2 at ventilatory threshol d there would also be a decrease in caloric expenditure as the number of calories expended per minute is dependent upon the liters of oxygen consumed per minute. If there is a lower rate of oxygen consumption, then a lesser number of calories are being expe nded. This leads to an overall lesser training stimulus. Minute ventilation, rating of per ceived exertion (RPE), and RER were not different between modalities and intensities. Reporting that RER at ventilatory threshold was not found to be different between modalities indicates that substrate utilization (percent of fats and carbohydrates utiliz ed during exercise) for both types of running was similar also, as substrat e utilization can be determined based off of the RER value. Both of these studies indica te that aerobic capacity and heart rate are lower during underwater running. It is thought that with decreased limb loading along with added buoyancy of a flotation device s een in this type of underwater running, workload is decreased to a point that would reduce maximal cardiorespiratory as well as metabolic responses in wate r (Silvers et al., 2007).
8 Similar results to those found by Butts, et al. (1991) and Frangolias, et al. (1995), were observed in three subsequent studies, a ll of which also utilized DWR with buoyancy devices. Dowzer, Reilly, Cable, & Nevill (1999) compared the maximal physiological responses to treadmill running, SWR, and DWR. Participants included 15 trained male runners who each completed maximal intensity exercise tests on a land-based treadmill, during SWR, and during DWR using a flotat ion device. Both the SWR and DWR tests elicited a lower maximal VO2 and HR in comparison to land-based running, with DWR eliciting lower values than SWR for both measures. RER wa s found to be similar across all three modalities. Frango lias, Coutts, Rhodes, & Taunton (2000) completed a study which further supported the findings of a lower VO2 and HR during underwater running utilizing flotation devices. Their study comp ared physiological responses to treadmill and water immersion to the nec k. Participants included 10 male endurance runners who performed treadmill and water immersion running maximal VO2 tests during each as well as submaximal tests at ventilatory threshol d. The immersion test was completed using a flotation belt with the water level at the neck. VO2 was found to be lower during underwater running in comparison to the tr eadmill on land during submaximal tests, although it was found to be similar during maxi mal tests. HR was similar at and above ventilatory threshold, but was lower during prolonged underwat er running exercise below the threshold when compared to land-based values. Ve and RPE were both reported to be similar during both modalities. The third study reporting lower VO2 and HR values during underwater treadmill running was co mpleted by Svedenhag &Seger (1992), and investigated the effect of water immersion on cardiorespira tory responses during running. Participants included 10 traine d male runners, mean age of 26 years old, who each ran in
9 water at four different submaximal load s at the target HRs of 115, 130, 145, and 155bpm wearing a buoyancy vest, as well as at maximal exercise in tensity. Values were obtained for land-based treadmill running at the same submaximal and maximal loads for comparison. HR for a given VO2 was seen to be lower during underwater running compared to land-based treadmill running, irrespective of intensity. Maximal VO2 and maximal HR were also seen to be lower during underwater running. RPE and RER were seen to be higher during underwater runni ng in comparison to land treadmill running, while Ve was seen to be the same across modalities. Svedenhag & Seger (1992) postulate that the results found in th eir study are likely due to wa ter immersion inducing acute cardiac adjustments extending to maximal exercise intensities, external hydrostatic load, and altered running technique adding to an increased anaerobic metabolism during water running. These studies cumulativ ely reported a decreased VO2 at both maximal and submaximal levels during water immersion r unning in comparison to land-based running. The cases reporting VO2 at submaximal levels to be lower indicate a decreased caloric expenditure as well. These studies also cumu latively reported RER to be similar for both types of running at both maximal and submaxim al levels, which indicates that there is no difference in the substrate ut ilization seen during water r unning in comparison to land running. In contrast to the previously discus sed studies, another study physiologically comparing deep water running using a flotati on device to land-based treadmill running by DeMaere & Ruby (1997) did not find VO2 and HR to be lower during underwater running. This study utilized DWR with flotati on devices in the deep end of a university pool. Participants included 8 seasonally trained male cross country runners, who each
10 completed a treadmill maximal VO2 test followed by treadmill submaximal test and deep water run at heart rates equi valent to 60 percent and 80 percent of the land-based treadmill VO2s. Pertaining to the protocol of this study, most authors writing on related topics caution against using land-based VO2 to prescribe water base d exercise intensities. This is because prior studies have shown conflicting results as to whether the modalities elicit similar responses, so there may be a difference in modalities that do not allow for prescribing one type of exercise based o ff of the other. Ve, RER, and carbohydrate oxidation were found to be greater during underwater running than treadmill running, while VO2 and RPE did not differ significantly be tween modalities. This study did not observe VO2 during water running to be any different than that observed during landbased treadmill running. Other studies investigat ing underwater running using alternative methods to flotation devices have elicited contrasting results from the pr eviously literature, as well. Most, if not all prior studies pertaining to this topic area utilizi ng underwater treadmills have not reported VO2 and HR to be lower in any case. This would suggest that if the VO2 is not lower, then the caloric expenditure for water treadmill running also will not be lower. Pohl & McNaughton ( 2003) compared the physiologica l responses of walking and running at ventilatory threshold utilizing a land treadmill to water treadmill responses at two different depths. Participants include d six males who each completed five minute walking and running trials on both land treadm ills and water treadmills. The water-based trials were complete at both thigh high a nd waist deep water levels. Walking and running on the underwater treadmill elicited a higher VO2 and HR in comparison to the landbased treadmill. VO2 and HR were seen to be higher during thigh deep running in water
11 than during waist deep wate r running. The authors state that water-based running and walking appear to elicit a gr eater physiological cost than land-based exercise, possibly attributed to the elevated co st of moving in water due to increased resistance. The most recently published study investigating underwater running in comparison to land-based treadmill running was done by Silvers et al., (2007) and aimed to determine the cardiovascular responses elic ited during maximal effort pr otocols using an underwater treadmill and land-based treadmill. This investigation was done to delve into the question of whether underwater running is able to elicit comparab le cardiorespiratory stress compared to land exercise, as it is a subject area that remains unclear. The participants included 23 college runners, who performed two continuous, incremental maximal VO2 protocols to exhaustion. VO2, HR, RER, RPE, and ventilatory thresholds were all found to be not significantly different between modalities, while Ve was the only variable seen to be significantly greater during underw ater treadmill running. The conclusions drawn by this study, as stated by the authors, indica te that the fluid resistance created by water and jets that are part of underwater treadm ill utilization elicit peak cardiorespiratory responses comparable with those seen during land-based treadmill running. This suggests that underwater treadmill running may be just as effective as land treadmill running for aerobic conditioning in fit individuals, from which it could be assumed that caloric expenditure and substrate utilization would be similar between th e two modalities. The results of the present study are expected to most closely resemble the results of the Silvers et al., (2007) study just discussed, as it used similar parameters and utilized an underwater treadmill (Hydroworx 2000) similar to that used in the present study (Hydroworx 1000).
12 While the vast majority of the resear ch that has been conducted on underwater running in comparison to landbased running has utilized DW R with flotation devices which seems to elicit lower VO2 and HR values than on land, th ere is still a broad area of underwater running using alternative modaliti es such as underwater treadmills which seems to elicit different responses warranti ng further research. SWR in comparison to DWR also elicit differing metabolic responses to each other, which both further differ from underwater treadmill running. Based off of the findings of Pohl & McNaughton (2003) and Dowzer et al., (1999), the lo wer the water level, the higher the VO2 and HR responses that are elicited will be duri ng buoyancy aided underwater running. Dowzer et al. (1999) states that this may be due to buoyancy counteracting the resistance of water, which lowers the physiological co st of movement in water. Metabolic and mechanical functions are altered when the body is submersed in water, and therefore differ dur ing underwater running compar ed to land-based running. Cardiorespiratory and metabolic responses seen during underwater running vary from that of land running, and also vary between types of underwater running. Underwater treadmill running is thought to account for more of the differences encountered in water in order to elicit metabolic re sponses and gait performance clos er in similarity to that observed on land. DWR with the aid of flotation devices on the other hand, does not as closely imitate land locomotion during running, and therefore elicits responses further from that of land-based running. According to the majority of th e literature, DWR is associated with lower VO2 (and therefore caloric expenditure ) and HR values than that of land-based running, and underwater treadmill runni ng is associated with values that are not significantly different than land-based running. These con cepts are still inconclusive
13 though, and have not been consiste nt across all of the prior st udies done in this area. It remains unclear whether underwater running is as efficient and effective a modality as land-based running. The goal of the present study is to gain further insight into the metabolic costs of underwater treadmill runni ng in comparison to land-based treadmill running, specifically in terms of caloric expe nditure and substrate ut ilization (percent of fats and carbohydrates utilized), at both maximal and submaximal levels.
14 Chapter Three Methods Participants Eleven volunteer participants were recrui ted from local triath lete training groups in the Tampa Bay area, primarily through word of mouth describing the nature of the study. One participant dropped out during the course of the study due to scheduling conflicts, and his data were omitted during statistical analysis. A second participant completed the water trials only, for a total of 4 of the 6 trials. His data were used where appropriate. The final sample consisted of 10 experienced male triathletes, ages 20-46. Experienced triathlete was defined by having completed at least two triathlons in the last year or having completed more than 5 tr iathlons in their lifetime, and participants also were required to be currently tr aining a minimum of 10 hours per week. No monetary compensation was offered to the participants; however their incentive for participating was to gain the knowledge of their maximal oxygen capacity to be used for training purposes. Prior to including any particip ant in the study they were required to fill out an informed consent approved by the University of South Floridas IRB, as well as a medical and training history questionnaire administered by a licensed physician. The average age, height, weight, and body mass index of the participants was 32.7 years (.6), 182.4 centimeters (.2), 79.3 kg (.8) and 23.9 BMI (.9), respectively. The average numbe r of Sprint Triathlons, Ol ympic Triathlons, Half Iron
15 Men, and Full Iron Men completed was 13.1 (.5), 4.4 (.4), 1.9 (.3), and 1.4 (.3) respectively, and the average number of y ears training was 8.2 (.1). During the year prior to participating in the study the av erage miles ran per week was 22.9 (.6), the average hours biked each week was 6.5 (.7), and the average hours swam each week was 2.5 (.7). Table 1 provides demographic data for the participants. Table 1 Participant Demographics (n=10) Mean (SD) Minimum Maximum Age (yrs) 32.7 (10.6) 20 46 Height (cm) 182.4 (5.2) 174 190.5 Weight (kg) 79.3 (11.8) 56.8 94.5 BMI 23.9 (2.9) 17.96 28.26 Years Training 8.2 (7.1) 2 25 Sprint Triathlons 13.1 (23.5) 0 75 Olympic Triathlons 4.4 (5.4) 0 15 Half Iron Man 1.9 (3.3) 0 10 Full Iron Man 1.4 (2.3) 0 7 Miles Ran (per wk.) 22.9 (10.6) 10 40 Hrs Biked (per wk.) 6.5 (4.7) 2 15 Hrs Swam (per wk.) 2.5 (1.7) 1 6 Experimental Design The research design used was a quasi e xperimental, 2 x 3 repeated measures design. 2 (maximal and submaximal aerobi c capacity tests) x 3 (modalities: water treadmill barefoot, water treadmill with shoes, land treadmill). It was designed to investigate the effects of underwater tr eadmill running with and without shoes in comparison to land-based treadmill running.
16 Protocol Each of the 10 participants completed si x experimental trials with the exception of one participant who complete d only four trials. Three of the six trials were maximal VO2 tests and three were submaximal aerobic capacity (VO2 submax) tests performed at 70 percent of maximal VO2. One maximal and one submaximal trial were completed for each of the three modalities being compar ed which included running on a Hydroworx underwater treadmill barefoot, running on a Hydroworx underwater treadmill with AQx brand water running shoes, and running on a land-based treadmill in a mostly random order (Table 2). The participant completing only four trials comp leted two maximal and two submaximal tests, one each for underwater barefoot as well as underwater with shoes. Maximal trials were completed prior to th eir corresponding submaximal trials and were used to establish the workloads for the s ubmaximal trials. AQx brand deep-water training shoes were used during the appropriate trials in this study in order to determine their effectiveness in comparison to running on water treadmills barefoot, as well as on land-based treadmills. These shoes are designed to simulate running on land without the associated impact of running on land, and are thought to be more similar to land running than running in the water barefoot. The pr esent study utilizes one aspect of a second study investigating these shoes. While the main purpose of the present study was to compare caloric expenditure and oxidative sources of underwater treadmill running in general to land-based running, the AQx water running shoes were included as a variable of interest to further establish their effectiveness as a mechanism to enhance water running. Inclusi on of the AQx shoes also lends ad ditional research literature to what is currently known regarding water treadmill running.
17 Table 2 Trial Conditions Completed by Each Participant Max. Trial Submax. Trial @70% VO2 max Land-Based UW with shoes UW without shoes Prior to completing their first trial, each participant met with a licensed physician who is also an investigator of the study to complete thei r medical and training history questionnaire as well as their University of South Florida Instit utional Review Board approved informed consent. The purpose and pr ocedures of the study were also explained to them, as well as their right to withdraw from the study without consequences at any time should they choose. At the beginning of each participant s first trial on the Hydroworx underwater treadmill, they co mpleted a 5 minute familiarization bout to acclimate them to the underwater treadmill as well as to the AQx underwater running shoes. Upon completion of the familiarization bout, they rested for approximately 2 minutes and then completed the trial. Note th at no participants had experienced running on an underwater treadmill prior to this study. Maximal trials were completed prior to their corresponding submaximal trials of the same modality, as the workload for the submaximal tests were based on a percentage (70%) of the aerobic capacity found during the maximal trials. Participants were requested to refrain from doing any type of exercise at any intensity for 12 hours prior to each trial, to refrain from doing any strenuous exercise 24 hours prior to each trial, and to refrain from eating 4 hours prior to each trial. They were instructed to come to each trial fully hydrated (as interpreted by each individual participant). Participants were also instructed to complete a 3-day food and exercise diary
18 prior to each trial in order to account for any dietary in take that may affect their performance. Each trial was separated by at least 48 hours, and was not supposed to be separated for more than one week; however due to unforeseeable events there were some trials that were separate d by more than a week. Maximal tests Maximal trials were conducted using an incremental protocol to volitional exhaustion. The land-based treadmill tests were started at a self-s elected, moderately vigorous pace that was held constant for the duration of the test. This pace was determined just prior to beginning the test during a brief warm up period lasting 1 to 5 minutes. The treadmill grade was increased by 2% every two minutes until exhaustion occurred. The maximum speed reached for land-based treadmill trials was 8.7mph with an average of 7.43 mph (1.17), and the maximum grade reach was 12% with an average of 9.5% (.2). The maximal underwater treadmill tests were done using a modified Astrand ramp protocol, similar to that used in an underwater treadmill study utilizing a Hydroworx 2000 treadmill by Silvers, et al. (2007). Prior to beginning the trial, the water level in the Hydroworx pool was adju sted to be just below the participants xiphoid process while standing in the pool. The je ts in the front of the pool were set at 40% resistance to start, as determined by S ilvers, et al (2007) to promote normal running gait and minimize float time over the treadmill belt. The participants began the trial at a self-selected, modera tely vigorous pace determined during the brief warm up period lasting 1 to 5 minutes just prio r to completing the test. For the first 4 minutes of the test,
19 treadmill speed was increased .5mph every 1 minute while maintaining 40% jet resistance throughout. At the end of minute 4, jets were increased 10% every 1 minute until volitional exhaustion was reached. In some cases, the maximum jet resistance (100%) possible was reached prior to the par ticipant reaching exhaus tion. In these cases speed was increased .5mph per minute until th e participant then reached exhaustion, or the Hydroworx treadmills maximum speed of 7.5mph was reached and maintained for a full minute. The average speed of the underw ater trials barefoot and with the AQx shoes were 7.27mph (.45) and 7.21mph (1.17) respectively, the average jet resistance was 95% (8.5) for barefoot, and 95% (7.1) with AQx shoes. Six participants reached maximum speed and jet resistan ce during their underwater VO2 maximal tests; however only 2 participants thought they may have been able to continue if it were possible to increase speed or jets any further. For thes e 6 participants, 5 met the criteria for reaching a maximal effort for the variable of HR (HR was greater than 90% of age predicted maximal) and 4 met the criteria for RPE (w ere at a score of 19 or 20 on Borg 6 20 scale). Only 2 participants met the criteri a for maximal exertion for RER (RER greater than 1.15); however, all of the participants had an RER greater than 1.0. (Note: No flotation devices or teth ering systems were used for the water trials). Prior to each VO2 maximal test resting heart rate (HR), resting blood pressure (pre BP), and weight were measured. Participants were allowed to warm up for 1 to 5 minutes at their discretion, and then th e trials took place. During the final minutes of the trials, verbal encouragement was employed to help ensure that a maximal effort was reached. After reaching exhaustion, participants were allowed to cool down for 1 to 5 minutes at
20 their discretion, and then resting post blood pressure (post BP) was measured. During each maximal trial HR and physiological data including oxygen consumption and RER was measured continuously. HR was r ecorded every minute, RPE was assessed every 2 minutes, and blood pressure was meas ured pre and post test. Blood pressure during maximal trials was only taken pre and po st test and not throughout the duration, as it was not feasible to obtain accurate readings during the trials specifically during running on the underwater treadmill. Table 3 Maximal VO2 Trial Protocols Incremental Protocol Speed Mean (SD) Workload Mean (SD) Water Treadmill 40% jet resistance; moderate ly vigorous 7.3mph (.34) 95%jets (8.5) (barefoot) pace. Increase speed .5mph/min for 4 min. then increase jets 10%/min. until exhaustion Water Treadmill 40% jet resistance; moderate ly vigorous 7.2mph (.45) 95%jets (7.1) (with AQx shoes) pace. Increase speed .5mph/min for 4 min. then increase jets 10%/min. until exhaustion Land Treadmill moderately vigorous pace 7.4mph (1.17) 9.5%grade (2.2) constant speed increase grade 2%/min. until exhaustion
21 Submaximal Tests Each submaximal trial was performed for 30 minutes at a workload that was calculated to be 70 percent of the participants respective maximal aerobic capacity: Land-based submaximal treadmill trial was done at 70 percent of the maximal VO2 found during land-based maximal treadmill trial. -Underwater with shoes submaximal trial wa s done at 70 percent of the maximal VO2 found during underwater with shoes maximal trial. -Underwater without shoes submaximal trial was done at 70 percent of the maximal VO2 found during underwater without shoes maximal trial. The speed and workload of the submaximal trials was determined based off of the participants corresponding maxi mal test data. The maximal VO2 value was multiplied by .7 to determine 70 percent, and the resulti ng value was compared to the maximal test data output to determine what workload th e participant was at when they reached 70 percent. This was the workload then us ed for the duration of the corresponding submaximal trial. Since it was difficult to se t a workload that was precisely 70 percent of an individuals maximal VO2, there was a variation fr om 70 percent that was on average .2ml/kg/min, .4ml/kg/min., and 3.41ml/kg/min for the barefoot trials, AQx shoe trials, and land-based trials respec tively. Previous related studies have set submaximal VO2 tests at 60-80 percent of maximal VO2 or at ventilat ory threshold, and the participants used in the present study we re triathletes and therefore highly trained. This seemingly supports 70 percent of maximal VO2 to be an acceptable intensity for the submaximal tests performed during this st udy (Frangolias et al. 1995, Frangolias et al. 2007, DeMaere & Ruby 1997, and Pohl & Mc Naughton 2003). Prior to commencing
22 each trial, resting HR, resting BP, and weight were measured. Participants were then allowed a 1 to 5 minute warm up period, follo wed by 30 minutes of simply running at 70 percent of maximal VO2 with no change in pace, grade, or jet resistance throughout. HR and physiological data including oxygen consumption and RER were measured continuously, RPE was assessed every 5 minutes and BP was taken pre and post test. It was not feasible to take BP during the tests, especially in the case of the water trials. Table 4 Submaximal VO2 Trial Values Avg. VO2 for Trial % of VO2max Speed Mean (SD) Workload Mean (SD) Water Treadmill 36.0ml/kg/min (7.6) 69.5% (8.5) 6.4mph (.43) 46% jets (8.4) (barefoot) Water Treadmill 38.3ml/kg/min (5.9) 70.8% (7.0) 6.2mph (.44) 43% jets (7.1) (with AQx shoes) Land Treadmill 40.8ml/kg/min (4.6) 76.6% (25.5) 6.9mph (1.0) .6% grade (1.0) Measures The trials took place at the University of South Floridas Tampa campus, either in the Athletic Training Facility or in the Exercise Science Teaching Lab. All water-based trials took place in the Athletic Training Facilitys Sports Medicine clinic on a Hydroworx 1000 treadmill consisting of a vari able speed treadmill with an integrated underwater treadmill surface, at the bottom of an adjustable pool. The speed range of this treadmill is 0 to 7.5mph, which could be incr eased by .1mph. The pool it was in was 7 wide, 14 long, and 5 deep, with a 2,100 ga llon capacity. Water leve l in the pool could
23 be raised or lowered to a pe rsons xiphoid process for trials by utilizing a control panel which allowed the water to drain into reserve tanks or to be pumped back into the pool. Water jets were inset at the front of the pool to provide water flow resistance which could be increased or decreased from 0 to 100% resistance using the control panel. The land-based trials took place in the Athletic Training Facilitys Strength and Conditioning room when possible, but due to scheduling conflicts and participant availability, 6 land-based trials were comple ted in the Exercise Science Teaching Lab. The land trials conducted in the Athletic Training Facility we re done on a Woodway treadmill; those done in the Exercise Scien ce Lab were done on a Trackmaster RS-232 treadmill. HR, BP pre and post, RPE, VO2, RER, caloric expenditure, and substrate oxidation were the variables of interest to be measured during the study. Caloric expenditure and substrate oxida tion were only calculated for submaximal trials. HR was monitored continuously using a Polar Heart Rate Monitor (Polar, USA) which the participants wore strapped to their chests. BP was measured at the beginning and end of each trial using standard pressure cuffs and sphygmomanometers. RPE was assessed every 2 minutes during maximal tests and ever y 5 minutes during submaximal tests using the Borg 15 point (6 20) scale. This scale wa s explained to the participants at the start of the study prior to beginning th eir first trial to ensure they knew how to read and use it accurately. Exertion was indicated by particip ants using hand signal responses to the numerical chart held in front of them while they ran. Metabolic measurements including VO2 and RER were assessed via expired ga s collection analyzed by a Vacumed metabolic measurement system which was approp riately calibrated prior to each trial. For
24 maximal tests the highest VO2 and RER values measured were the values used. For the submaximal tests the average VO2 and RER values measured from minute 2 through minute 30 of the trials were the values use d. (Minute 1 values were not used in the average as the participant had not yet reached 70 percent of their maximal VO2). VO2 and RER determined using the metabolic measurement system were used to calculate each participants caloric expenditure (in kilocalo ries) as well as their substrate utilization (in percentage of fats and carbohydrates). Th is method of indirect calorimetry, according to Robergs and Kravitz (1992), is the most suitable and accurate method to evaluate caloric expenditure during exercise. Percent of carbohydrates oxidized and of fat oxidized during each trial was determined by comparing the RER to the Caloric Equivalents for Oxygen and Foodstuff Contributions to Ener gy for Various Non-protein Respiratory Exchange Ratios chart. Caloric expenditure was calculated using the appropriate formula for extrapolating calories utilized from VO2 according to ACSMs Metabolic Calculation Handbook taking into account RER. Wa ter temperature was monitored using the pool thermometer, and ranged fr om 20.6 -35.6 degrees Celsius even though the aim was to maintain the temperature within 2 -4 degrees. This temperature range is broad due to factors acting outside of the study whic h will be discussed later. On average the water temperature was 25.8 degrees Celsius (78.5 degrees Fahrenheit). All measurements were recorded by hand using data collection sheets, with the exception of the metabolic carts measurements, which were printed out at the end of each trial.
25 Statistical Analysis Maximal trials were completed prior to their corresponding submaximal trial in order to establish submaximal workload; how ever the order by which the trials were completed was mostly random and based on scheduling availability. Each participant served as their own control. Descriptive statistics, repeated measures ANOVA, and paired t-tests were performed using SPSS 17.0 soft ware to analyze the effects of the three modalities being investigated (water treadmill barefoot, water treadmill with AQx shoes, and land treadmill) for each dependent variable If statistical significance was found for a variable, follow up pairwise comparisons were conducted between modalities using Bonferroni adjustments. Analyses were perf ormed for the dependent variables including: HR, RPE, VO2, BP, RER, caloric expenditure, substr ate utilization, as well as for other dependent variables that were not of primary interest in th is study. Significance level for all tests was set at p < 0.05 and effect size was determined using the formula d = t *(2 (1-r)/n) ^1/2 shown to be effective for repeated m easures analysis (Dunlap, W., Cortina, J., Vaslow, J., & Burke, M., 1996). Th e variables used in this formula d, t, r and n are defined as effect size, t-score, correlation value, a nd sample size, respectively. Effect size was considered small at d = 0.2, medium at d = 0.5, and large at d = 0.8.
26 Chapter Four Results Descriptive statistics including mean and standard deviation, as well as significance values are presented in Tables 5 and 6 below, for maximal and submaximal trials as groups respectively. For each de pendent variable, repeated measures ANOVAs were performed for all trials to see if th ere was a significant difference. If there was a difference, pairwise comparisons were conducted between the 3 modalities for the variable of interest, using Bonferroni adjustments to determine which modalities the significant difference existed between. Pair ed samples t-tests were performed to determine t-value and correlation for each va riable, across all 3 modalities (3x for each variable). These values were then used to calculate effect size using the equation established to be effected for repeated meas ures by Dunlap et al. (1996). Effect size for all variables was taken into c onsideration for effects of this study due to the low subject number (n=10) and weak power. De pendent variables included HR, VO2, RPE, RER, BP pre and post, caloric expenditure, and substr ate utilization (percentage of fats and carbohydrates utilized). Caloric expenditure and substrate utilization were the primary variables of interest, and were dete rmined for submaximal tests only.
Table 5 Maximal Test Results Water Treadmill Barefoot Water Treadmill with Aqx Shoes Land Treadmill Mean (SD) Mean (SD) Mean (SD) P value VO2 Max (ml/kg/min) 51.79 (8.7) 54.08 (5.7) 53.28 (6.4) 0.848 HR Max (bpm) 174.2 (10.2) 174. 0 (14.6) 187.2 (14.7) .018* RPE Max 18.6 (.88) 19.5 (.71) 18.8 (1.2) 0.113 RER Max 1.09 (.1) 1.11 (.11) 1.17 (.04) 0.394 Pre SBP 123.3 (9.2) 120.9 (8.3) 114.6 (9.8) 0.091 Pre DBP 74.1 (9.0) 70.8 (6.1) 71.1 (11.0) 0.35 Post SBP 123 (7.5) 122.7 (18.3) 121.3 (11.8) 0.536 Post DBP 73.6 (5.7) 75.6 (10.0) 75.1 (16.4) 0.201 *Indicates significance was found for p < 0.05. Table 6 Submaximal Test Results Indicates Significance was found for p < 0.05. Water Treadmill Barefoot Water Treadmill with Aqx Shoes Land Treadmill Mean (SD) Range Mean (S D) Range Mean (SD) Range P value VO2 avg. (ml/kg/min) 36.4 (7.9) 22.1 5.7 39.1 (5 .6) 31.0 -48.2 40.8 (4.6) 31.4 -5.9 .014* HR avg. (bpm) 140.3 (11.0) 127 160 148.0 (16.7) 125 178 150.0 (9.2) 141 -172 0.137 RPE avg. 13.5 (1.2) 12 15 14.0 (2.0) 13 19 12.7 (.50) 12 13 0.27 RER avg. .93 (.05) .86 .99 .92 (.04) .85 .99 .92 (.04) .87 .99 0.77 Total Calories 410.6 (66.7) 275 486 442.6 (69.4) 257 510 487.3 (41.9) 434 -554 .012* %Fats Utilized 24.1 (16.1) 3.2 45.9 26.0 (1 3.5) 3.2 49.3 24.9 (12.4) 3.2 2.5 .896 %Carbs Utilized 76.0 (16.1) 54.1 6.8 74. 0 (13.5) 50.7 -96.8 75.1 (12.4) 57.5.8 .896 Pre SBP 114.3 (6.5) 108 126 116.4 (6.7) 104 128 124.7 (5.9) 118 -132 .004* Pre DBP 68.9 (5.7) 60 80 75.0 (7.8) 60 69.3 (8.2) 60 80 0.227 Post SBP 116.2 (7.8) 104 130 115.3 (10.4) 98 134 124.7 (4.1) 120 -130 0.288 Post DBP 71.2 (8.3) 60 80 73.9 (10.8) 52 86 67.3 (12.4) 52 0.487 27
28 Test of Hypotheses There were four primary hypotheses test ed in this study, two null hypotheses (Ho) tested against two altern ative hypotheses (Ha). Ho1 stated that there is no significant difference in the caloric expenditure during water treadmill running versus land-based treadmill running at submaximal exercise intens ities. The results showed that there was a significant difference between water treadmill running and land treadmill running (p = 0.045), and therefore we reject the null hypothesis. This does not mean we can accept the alternative (Ha1), which stated that water treadmill running would elicit a greater caloric expenditure than land treadmill running at subm aximal exercise intensities. The results showed a significant difference between the two modalities, but in comparing the means land treadmill running elicited a greater calo ric expenditure than water treadmill running. The means for running on the water treadmill barefoot, water treadmill with shoes, and land treadmill were found to be 410.8kcals, 442.6kcals, and 487.3kcals, respectively. See table 7. Table 7 Caloric Expenditure (descriptive data) Mean (SD) Range Water Treadmill Barefoot 410.8 kcals (66.7) 275.2 486.5 kcals Water Treadmill With Shoes 442.6 kcals (69.4) 257.9 509.8 kcals Land Treadmill 487.3 kcals (41.9) 434.1 554.3 kcals P-value for Caloric Expend iture (main): p = .012
29 Table 8 Caloric Expenditure (pairwise comparisons) P value ES Correlation r T-score Water Barefoot vs. Water With Shoes 0.271 0.46 0.65 1.75 Water With Shoes vs. Land 0.564 0.7 -0.05 1.44 Water Barefoot vs. La nd .027* 1.34 0.32 3.44 *Indicates significance. (p < 0.05) Ho2 stated that there is no significant difference in the substrate utilization (percentage of fats and carbohydrates) during water treadmill running versus land-based treadmill running at submaximal exercise intensities. The results found supported Ho2, indicating no significant difference exists in substrate utilization during water treadmill running compared to land treadmill running (p = .896), therefore we fa il to reject the null hypothesis. In failing to reject Ho2, we accept it, and theref ore can not accept the alternative hypothesis (Ha2) which states that water tread mill running will have a greater utilization of calories from carbohydrates than land-based treadmill running at submaximal exercise intensities. Compari ng the mean values of percent carbohydrates and fats utilized supports the null (Ho2), as shown in table 9. Table 9 Substrate Utilization (at submaximal levls) Fats Utilized Mean (SD) Carbs Utilized Mean (SD) Fats Utilized Range Carbs Utilized Range Water Treadmill Barefoot 24.1% (16.1) 75.9% (16.1) 3.2 45.9% 54.1 96.8% Water Treadmill With Shoes 26.0% (13.5) 74.0 (13.5) 3.2 49.3% 50.7 96.8% Land Treadmill 24.9% (12.4) 75.1% (12.4) 3.2 42.5% 57.5 96.8% P-value for percent fa ts utilized: p = .896 P-value for percent carb ohydrates utilized: p = .896
30 Contributing Variables Statistical analysis was done for the dependent variables of HR, VO2, BP pre and post, RPE, and RER which were not of primar y concern to the research question. For the maximal tests VO2 max. (p = .848), RPE max. (p = .113), RER max. (p = .394), BP pre systolic (p = .091) BP pre diastolic (p = .350) BP post systolic (p = .536), and BP post diastolic (p = .201) were all found to be non-significant acro ss all 3 modalities. For the submaximal tests average HR (p = .137), average 70% of maximal VO2 (p = .713), average RPE (p = .270), average RER (p = .770) percent fat utilized (p = .896), percent carbohydrates utilized (p = .896), BP pre diastoli c (p = .227), BP post systolic (p = .288), and BP post diastolic (p = .487) were all f ound to be non-significant. For the maximal tests HR max. was the only variable found to be significant (p = .018). For the submaximal tests average VO2 (p = .045), calories expended (p = .012), and BP pre systolic (p = .004) were found to be significan t. For the significant variables, pairwise comparisons were performed. Interestingly, after completing pairwise comparisons, all variables of significance were found to be significantly different between the water treadmill barefoot and land treadmill tests only. See tables 5 and 6 for descriptive statistics and main significance. Table 10 prov ides data for the pairwise comparisons of the significant variables.
Table 10 Pairwise Comparisons for Variables of Significance *Indicates significance (p < .05) Water Barefoot and With Shoes Water With Shoes and Land Water Barefoot and Land P value ES P value ES P value ES HR max (bpm) 1 .02 1.52 0.97 0.048* .99 VO2 avg. (ml/kg/min) 0. 223 0.31 0.604 0.31 0.043* 0.45 Kcals (over 30 min.submax) 0.271 0.46 0.564 0.7 0.027* 1.34 Pre systolic BP (submax) 0.105 0.56 0.174 1.23 0.057* 2.32 It is also interesting and important to note that a large effect size (ES) was found for a number of variables that were not found to be significant. This could potentially be due to the small sample size used in this study (n=10) which gives it a weak power. For submaximal tests the ES was large for HR compared between wate r barefoot and land (ES = .90), RPE compared between water barefoot and land, and water with shoes and land (ES = .77 and ES = .84), pre diastolic BP compared between water barefoot and with shoes (ES = .87), and for post systolic BP compared between water barefoot and land, and water with shoes and land (ES = .94 and ES = .86). None of these variables were found to be significant, though. For maximal te sts the ES was large for HR compared between water with shoes and land (ES = .97), RPE compared between water barefoot and with shoes (ES = .84), RER compared between water barefoot and land (ES = .84), and compared between water with shoes and la nd for pre systolic BP (ES = .88). None of these were found to be significant, though. For the four variables th at were found to be significant (p < 0.05), all but one had a larg e ES. Those variables include average VO2 compared between water barefoot and land (ES = .45; not large), calories expended 31
32 compared between water and land (ES = 1.34), pre systolic BP compared between water and land (ES = 2.32), and maximal HR compar ed between water and land (ES = .99). This is shown graphically in figures 1, 2, and 3.
0 20 40 60 80 100 120 140 160 180 200 Vo2 MaxHR Max *RPE MaxRER Max Water Treadmill Barefoot Water Treadmill with Aqx Shoes Land treadmill Figure 1. Results of Maximal Oxygen Consumption Trials Significant difference be tween trials, p < 0.05. 33
0 20 40 60 80 100 120 140 160 Vo2 Avg. *HR Avg.RPE Avg.RER Avg. Water Treadmill Barefoot Water Treadmill with Aqx Shoes Land treadmill Figure 2. Results of Submaximal Oxygen Consumption Trials Significant difference be tween trials, p < 0.05. 34
0 50 100 150 200 250 300 350 400 450 500 Total Calories *%Fats Utilized % Carbs Utilized Water Treadmill Barefoot Water Treadmill with Aqx Shoes Land treadmill Figure 3. Submaximal Calories and Substrates Utilized Significant difference be tween trials, p < 0.05. 35
36 Chapter Five Discussion Results of the present study indicate that running on a water treadmill both barefoot and with the AQx brand underw ater training shoes may elicit similar cardiorespiratory responses to land-based r unning during maximal aerobic capacity trials, but elicit results that vary from land-based running during submaximal intensity trials. Silvers et al. (2007) found no si gnificant differences for VO2, HR, RER, or RPE when comparing water treadmill running to land-based treadmill running at maximal capacities. This supports the findings of the present study which found VO2, RER, RPE, and BP to have no significant differences at maximal ex ertion; with the excep tion of HR which was found to be greater during land-based treadmill running. A number of previous studies utilizing underwater running without an underw ater treadmill have noted a greater HR on land than in the water also, which is likely due to the hydrostatic effect caused by water immersion (Butts et al. 1991, Frangolias et al. 1995, Dowzer et al. 1999, Frangolias et al. 2000, and Svedenhag & Seger 1992). The resu lts of the present study may also potentially be due to the water temperat ure during underwater treadmill trials being cooler than the ambient temperature of the ai r during land-based trials as HR is affected by temperature (Gleim & Nicholas, 1989). Inte restingly, the difference found for HR was only seen between running on a water trea dmill barefoot and running on a land-based treadmill, but there was no difference betw een running on a water treadmill with the
37 AQx brand shoes and running on a land treadmill. This suggests that for maximal exertion performance, the AQx shoes may elicit HR responses similar to that of landbased treadmill running. Outside of HR, all ot her variables were f ound to be similar for all 3 modalities during maximal trials, sugges ting that water treadmill running may elicit similar cardiorespiratory responses at maximal exertions. At submaximal capacities HR, RPE, RER, substrate utilization (percentage of fats vs. carbohydrates utilized), and BP were al l found to be similar for water treadmill running in comparison to land-based tr eadmill running. In contrast, average VO2, total calories burned during the 30 minute trials, a nd pre-exercise systol ic BPs were all found to be significantly lower during water tr eadmill running in comparison to land-based treadmill running at submaximal exertions. It was expected that water and land-based treadmill running would have elicited similar results for all variables at submaximal levels, but this was not shown in the results. It is interesting to note that for each variable that differed at the submaximal level (as we ll as at the maximal level), the significant difference was found between the barefoot water treadmill running in comparison to land-based treadmill running, but not for the water treadmill running with AQx shoes in comparison to land-based treadmill running. This lends further evidence to the concept that running on under water treadmills with the AQx brand shoes may elicit results that are more similar to land-based treadmill r unning than simply running on an underwater treadmill barefoot. While a difference in general was not expected, since average VO2 was significantly lower underwater than on la nd, it is not surprisi ng that the calories expended over the 30 minute duration of the submaximal tests were also significantly lower underwater compared to on land. Calories are measured in the amount utilized per
38 liter of oxygen consumed, so if the averag e number of liters of oxygen consumed per minute is lower, then it is expected that the number of calories expended would also be lower. There was a greater difference f ound for the calories expended across the 3 modalities than there was for the average VO2, though. The difference in average VO2 observed between underwater running and land running was less than the difference seen in caloric expenditure between the two, ev en though it would be expected that the differences should be similar. This may potentially be due to la nd running utilizing a greater percentage of carbohydr ates in comparison to fats which would elicit a great caloric expenditure at a given VO2 than if a greater pe rcentage of fats we re utilized at the same VO2. If this is the case then th e already existing difference in VO2 would be even greater when extrapolated into calories expended. When reviewing the results found in this study, it is important to take into the consideration the average work load of the submaximal trials, which were based on the maximal VO2 found during the maximal trials. While the goal for all submaximal trials was for their workloads to be set at 70 percent of the maximal VO2, they were actually performed at 69.5%, 70.8%, and 76.6% of maximal VO2 for the underwater barefoot, underwater with shoes, and la nd-based trials, respectively. Th is indicates that the landbased submaximal trials were performed at a higher percent of maximum, and therefore at a higher intensity than either of the water trials. If the land-based trials were performed at a higher intensity then it would be exp ected for them to expend a larger number of calories (as the results of this study demonstrated ). If all submaximal trials had been able to have been held closer to a consistent 70 percent of the max, there may not have been a difference noted in the average VO2 or caloric expenditure for the 30 minute submaximal
39 trials (Table 4). The reason it was seemingl y more difficult to control for submaximal VO2 levels at 70 percent on land than it was in the water may be due to the method of adjusting intensity on land versus in the water. Increasing jet resistance in the water by just 1% allowed for finer adjustments in workload, whereas increasing treadmill grade by 1% seemed to elicit greater adjustments in workload making it slightly more difficult to adjust to precisely 70 percent of maximal VO2. Earlier studies investigating underwater running without the use of underwater treadmills proposed that a decreased VO2 seen in the water may be due to the buoyancy effect and decreased limb loading which would reduce cardiorespiratory responses in the water as a result of an over all reduced workload (Silvers et al., 2007). The water jet propulsions exerted out of the front of the underwater treadmill pool at the runner were thought to oppose the effects of buoyancy to e licit a training response similar to that of land. The results of the present study found this to hold true at maximal levels, but not at submaximal levels. This may indicate that at stronger jet resist ances (reached during maximal exertions) the effects of buoyancy are opposed, but at the w eaker jet resistances (maintained during submaximal exertions) the effects are not enough to counteract buoyancy and so workload is less. Pre-exercise systolic BP for submaximal tests was also found to be significantly different between water treadmill running and land treadmill running, and was found to have a large ES. While this indicates that a real differenc e may be present, it does not logically seem to be a factor affected by the different modalities. BP may vary for a number of reasons but in this case it was th e BP taken before a participant completed a trial so the difference of whether the trial was done on land or in the water should not
40 have affected the outcome. Diurna l variations in BP would not have been a factor in this study, as all participants with the exception of one completed each of their trials at the same time of day throughout the study. RER at both maximal and submaximal levels was found to be similar between modalities of running, which is consistent with the majority of the prior literature (Butts et al. 1991, Dowzer and Reilly 1999, and Silv ers et al. 2007). Two previous studies (Reilly et al. 2003, and Svedenha g et al. 1997) reported a high er RER, but both of these studies utilized buoyancy devices during water running rather than water running alone or on an underwater treadmill. The findings of the current study showing RER to be similar for underwater treadmill running in compar ison to land-based treadmill running can be used to indicate that the subs trate utilization was also sim ilar for the two types of running. This can be seen when comparing RER values to the Caloric Equive lent for Non-protein Foodstuffs Contributions chart to determine the percentage of fa ts and carbohydrates utilized during exercise. The AQx underwater running shoes util ized in this study are designed to enhance underwater running and elicit res ponses to simulate land-based running. They have rubber traction bottoms and gills that protrude sligh tly off of the side of the shoe to increase resistance during locomotion through the water. During maximal intensity trials utilizing greater speeds and jet resistance, th e gills on the shoes seemed to pose an added resistance that a number of participants not ed to be uncomfortable and a hindrance. The jets seemed to catch the gills in itially as they shot of out the front of the pool directly at the participant, then catch th e gills a second time coming from the back of the pool as the water that was being propelled hit the back wa ll and circulated back towards the front of
41 the pool. There were mixed responses from the participants pertaining to the AQx shoes. Some participants noted that the shoes caused sharp pains in their anterior tibialis when running on the underwater treadmill in comparison to being barefoot; even to the point where one participant chose to terminate hi s submaximal trial wearing the AQx shoes 7 minutes early. Other participants; however, noted that they preferred running on the underwater treadmill using the shoes in comparison to being barefoot. This was because without the shoes they felt like they were slipping off of the treadmill and at higher intensities it was difficult to stay on the treadmill. The slipping that occurred on the treadmill also lead to blisters on the feet of 2 participants. The shoes provided traction to avoid slipping, and were found to be favorable for some participants. The participants who noted that they preferred the shoes to being barefoot duri ng underwater treadmill running, also stated that they did not experience any pain in their anterior tibialis. No formal data on preference of shoes vs. no s hoes was collected, but verbal questions were asked regarding the participants preference. There were some limitations of the st udy that were seemingly unavoidable. One aspect that was intended to be controlled fo r was the time separation of the trials. The original intent was to separate trials by no more than a week in order to avoid changes in VO2, weight, and other variables as a result of changing training status. If the trials were kept close together in time, then a change of training status would be less likely to affect the outcome of the study. Due to unforeseeable events such as participant availability, facility availability, and issu es with malfunctioning of the me tabolic cart used, there were approximately 5 trials separated by more than a week. Two of these tr ials occurred over a month after the previous trial, during which time the athl etes had altered their training
42 status. In one case the particip ant had been out for an injury and lessened training, and in the other the participant had started increas ing training notably. The other limitation that was intended to be controlled for was the pool temperature during water trials which ranged from 20.6 35.6 degrees Celsius, and averaged 25.8 degrees Celsius (78.5 degrees Fahrenheit). It was in tended to maintain the temperature within a 4 degree range; however, since the water treadmill and pool used was located in the Universitys Athletic Training Facility, athletes usi ng the pool when the study was not taking place were free to alter the temperature. There were also a pproximately 3 trials completed during a time when the thermostat of the pool would increase without manual alterations overnight, so when the pool was utilized the next morning for a trial the temperature would be higher than it would be ideally. This may have eff ect certain variables such as RPE and HR, but should not have affected th e primary variables of VO2, caloric expenditure, and substrate utilization to a large extent. Acco rding to previous literature, VO2 is not affected by water temperature (Gleim et al. 1989, Mcardle et al, 1992, and Craig & Dvorak, 1996). One other limitation of the study that should be noted for future research was that approximately 5 of the 10 participants reached the underwater treadmills maximal workload capacity (treadmill speed = 7.5mph and jet resistance = 100%) before they had reached their own maximal VO2. Only on two occasions did th e participants state that they felt they could have kept going after they reached and maintained this point for an entire minute, but it would have been benefici al to have been able to increase treadmill speed and/or jet resistance further to ensure that all participants reached their greatest maximal exertion.
43 The study utilized only healt hy triathletes as participants, so the results found are not generalizable to a normal population. Utilizing triathlete s is a good indicator for elite athletes such as runners who may be interested in underwater treadmill running as an alternate or supplementary means of trai ning to avoid the stress placed on their musculoskeletal system on land. Based on the findings of this study, underwater treadmill running at higher levels of exertion (near maximal) elicits cardiorespiratory and metabolic responses similar to those seen during land treadmill running. This does not generalize for water treadmill running at submaximal intensities as VO2 and caloric expenditure will not be as high as they would be during land treadmill running. These concepts are inconclusive though, as the result s of this study are consistent with some prior studies, but are not all prio r studies done in this area. It is also possible that the level of exertion an individual trains at while using an underwater treadmill may affect the similarity of the cardiorespiratory elic ited during running on a water treadmill versus running on a land treadmill. Furthermore, it is acknowledged that little is known regarding the reliability of wa ter exercise testing (Silvers et al, 2007). Further research should be done to determine reliability of underwater exercise testing, and to further investigate the cardiorespiratory respons es of underwater treadmill running in comparison to land treadmill running using di fferent levels of exertion and fluid jet resistance. It appears that th e goal of underwater running of al l types is to provide a form of supplementary training, injury prevention, and injury rehabilitati on without the impact and musculoskeletal loading of land-based running, while ma intaining the same training stimulus as land-based running. This supports the need for further research into
44 underwater running modalities in order to e licit the same responses as land-based treadmill running.
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