American Fitness Professionals & Associates

By Len Kravitz, Ph.D and J.J. Mayo, Ph.D.Part I.

The Training Effects of Aquatic Exercise
Water exercise is rapidly growing in popularity. Exercise enthusiasts, athletes, elderly, and the physically challenged are discovering aquatic exercise programs that suit their fitness desires. An advantage of aquatic exercise is that it can involve the upper and lower extremities through optimal ranges of motion while minimizing joint stress.
Despite the numerous attributes of aquatic exercise, few randomized, controlled studies have been completed substantiating the benefits of exercise in this medium. This review summarizes the published research, from articles and abstracts, and will be presented in three sections: 1) the training effects of aquatic exercise, 2) shallow and deep water exercise responses, and 3) selected topics of aquatic exercise.
The Aquatic Medium—800 Times as Dense as Air
Weight bearing, land-based exercise presents a challenge to the joints and soft tissues of the body. The repetitional strain imposed on the tissues by ground striking can lead to injury. The buoyant force of water results in up to a 90% reduction in body weight in the water. Because of the cushioning effect of water, individuals potentially at risk to bodily stress from weight-bearing exercise, such as the elderly, obese, individuals with a soft tissue injury, or those with an orthopedic disorder, may find water to be the most desirable environment for exercise. Yet, at the same time, water is capable of providing a full-body resistance. The density of water is approximately 800 times that of air, which is an important contribution to the energy cost of aquatic exercise (Di Prampero, 1986) . Thus, the water environment allows for high levels of energy expenditure with relatively little strain to the body.

Maximal Oxygen Consumption—Deep Water Running Training Studies
The majority of research completed on deep water running (DWR) has evaluated the ability to sustain (Bushman et al., 1997; Eyestone, Fellingham, George, & Fisher, 1993; Quinn, Sedory, & Fisher, 1994; Wilber, Moffatt, Scott, Lee, & Cucuzzo, 1996) or improve (Michaud, Brennan, Wilder, & Sherman, 1995) aerobic capacity following DWR. The cardiovascular and metabolic effects of chronic DWR versus land-based running is of particular interest to competitive runners suffering from musculoskeletal injury, or those wanting to reduce the stress associated with rigorous training. Table 1 summarizes the current research investigating the chronic effects of DWR training on maximal treadmill responses. Presently only a limited number of studies exist describing the training effects of DWR exercise programs. Due to variations in training programs, testing procedures and study lengths (4-10 weeks), conclusions are tentative.
Those studies conducted utilizing endurance trained subjects have found DWR training to be successful in the maintenance of aerobic performance (Bushman et al., 1997; Hertler, Provost-Craig, Sestili, Hove, & Fees, 1992; Wilber et al., 1996) . Wilber et al. recruited 16 trained male runners aged 20-40 years old to examine the effects of a 6-week DWR program on maximal oxygen consumption (VO2max), lactate threshold and running economy. The DWR training maintained maximal oxygen consumption (pre = 58.7 ± 4.7, post = 59.6 ± 5.4 ml/kg/min) in the highly fit subjects. These results are consistent with Bushman et al. who found similar maximal (pre = 63.4 ± 1.3, post = 62.2 ± 1.3 ml/kg/min) and submaximal VO2 responses (pre = 44.8 ± 1.2, post = 45.3 ± 1.5 ml/kg/min) after only 4 weeks of DWR training in 11 competitive runners (males N = 10; females N = 1; mean = 32.5 yr).
In the study conducted by Wilber et al. (1996), ventilatory threshold was sustained at approximately 80% of VO2max (Day 0 = 46.5 ± 6.14 ml/ kg/min, 79% VO2max, Day 42 = 47.4 ± 6.7 ml/kg/min, 80% VO2max), while VEmax (Day 0 = 120.1 ± 13.3 l/min, Day 42 = 131.1 ± 17.6 l/min) and treadmill run time to exhaustion (Day 0 = 16.6 ± 5.4 min, Day 42 = 17.3 ± 5.7 min) were not significantly altered through DWR training. Although DWR uses different proportions of upper to lower body muscle mass compared to land-based running, Wilber et al. and Bushman et al. (1997) both concluded that chronic DWR training created the physiological stimuli necessary to facilitate the maintenance of running economy.
Small inconsistent changes in maximal blood lactate responses have been reported after chronic DWR training (Bushman et al., 1997; Wilber et al., 1996) . Wilber et al. observed slight increases in maximal blood lactate values as a result of DWR training (7.8 ± 2.2 mM to 8.3 ± 2.0 mM) while decreases (pre = 9.3 ± 0.6 mM; post = 8.3 ± 0.5 mM) were noted by Bushman and colleagues. The heightened blood lactate response in the Bushman et al. study is most likely a reflection of greater VO2max values of these subjects.
Hertler et al. (1992) compared treadmill exercise to DWR training in 13 young runners (aged 18-26 yr). Subjects trained on land 3 days per week, for 4 weeks, and then half of the subjects began a DWR program while the rest continued to run on land. To equalize the training, groups were matched for total exercise time and RPE. Post-training maximal treadmill tests indicated no changes occurred in VO2max between the treadmill and DWR exercise training groups. This finding implies that DWR training can be effective in maintaining VO2max in aerobically trained subjects.
In a practical assessment of endurance performance, Bushman et al. (1997) had subjects complete a simulated 5-kilometer (5-k) run at a race pace on the treadmill to assess the crossover effects of DWR training to treadmill exercise. Analysis revealed that pre-training 5-k run times (1142.7 ± 39.5 s) were not significantly altered following 4 weeks of DWR training (1149.8 ± 36.9 s). Similarly, in an investigation by Eyestone et al. (1993) , 32 recreational trained runners (VO2max = 56.29 ± 1.49 ml/kg/min) achieved small but non-significant improvements (1.21%) in two-mile run performance (indoor track) after 6 weeks of DWR. However, post-tests revealed VO2max declined in these subjects by 4.9% (post-test VO2max = 53.52 ± 1.61 ml/kg/min).

This may just represent daily variations in VO2. Another possible reason for these decrements in VO2max by Eyestone’s subjects is that the exercise prescription used minimal standards accepted by the American College of Sports Medicine (ACSM) for maintenance of cardiovascular fitness during the entire study. The training regimen established by Eyestone and colleagues consisted of subjects initially training 3 days per week and increasing to 5 days per week during weeks 3-6. Duration of exercise was established at 20 minutes in week 1 progressing to 30 minutes during the final month. Exercise intensity began at 70% of heart rate maximum (HRmax) and increased to 80% HRmax over the last 4 weeks of the study. The hydrostatic effects of the water may have caused Eyestone et al. to underestimate the training heart rate during DWR. Along with daily variations in VO2 this underestimation of training intensity also could have been a major contributing factor leading to the decline in VO2max in these fit participants. In studies where VO2max has been maintained, exercise training has closely resembled land-based training.
Wilber et al. (1996) exercised aerobically trained subjects 5 days a week, alternating high intensity shorter workouts (90-100% VO2max for 30 minutes) with moderately intense longer sessions (70-75% VO2max for 60 minutes). Similarly, Bushman et al. (1997) employed a training regimen consisting of DWR 5-6 days a week integrating two long and short interval days, one long run and an easy recovery run. These training schedules not only reflect actual training routines of these competitive athletes but more importantly insure adequate exercise intensity for the maintenance VO2max.
Only one published training study investigated the effects of DWR with older adults (mean age of controls 57.5 ± 2.3 yr, mean age of experimental group = 63.1 ± 1.6 yr). In this investigation Long et al. (1996) reported significant VO2max improvements in a group of 35 sedentary older women after a 10-week DWR program.
Quinn and colleagues (1994) found that untrained females were unable to sustain VO2max though DWR. In their study, 7 young untrained females (mean = 21.7 yr) performed 6 weeks of land-based training (LBT) followed by 4 weeks of DWR. Evaluation of VO2max occurred on three separate occasions: before and after the land-based running training and at the conclusion of the DWR program. Participants trained 4 days a week for a duration of 30 minutes per day. Untrained subjects improved VO2max after 6 weeks of outdoor running (post-LBT = 42.9 ± 3.2 ml/kg/min) only to have these gains return to pre-training baseline values after 4 weeks of DWR (pre-training = 39.9 ± 3.6, post-DWR 40.0 ± 1.8 ml/kg/min). Similar to Eyestone et al. (1993), exercise training intensity during the DWR training protocol may have also effected the outcome of this study. Unlike the land-based training protocol which varied exercise intensity from 60-80% heart rate reserve (HRR), the DWR program employed only steady state exercise at one intensity (80% of HHR within 10 bpm). Since acute heart rate responses are decreased in water due to hydrostatic pressure, this steady rate intensity may not have been adequate to maintain VO2max. Upon completion of the project, the authors indicated the importance of adding interval, varying tempo and fartlek workouts to the DWR training routine. This suggests that there may be a critical intensity or threshold which must be achieved if VO2max is to be maintained or improved through DWR. The frequency and duration spent training at this critical threshold is yet to be elucidated.
Morrow, Jensen & Peace (1996) divided 11 subjects into either DWR (female = 3, males = 3) or land-based (female = 2, male = 3) exercise groups. Subjects trained three days a week for 35 minutes a session at 80% of HRmax as determined by mode specific VO2max tests. Additionally, subjects performed a timed 2.4-k run. Both training groups significantly improved in VO2max (p 0.07), in the sit-and-reach flexibility test (pre = 34.1 ± 2.1 cm, post = 36.6 ± 1.8 cm) after 8 weeks of deep water aerobic training. Sanders and Rippee (1994) combined both shallow and deep water exercise during 8 weeks of water aerobics. As part of the experiment subjects were separated into young (28 ± 6.5 yr) and older (52 ± 8.3 yr) adults. Results revealed small, non-significant, improvements in the sit-and-reach for the younger (pre = 15.9 in, post = 16.0 in) and older (pre = 12.8 in, post = 13.5 in) subjects.
Flexibility Summary
Current studies, although small in number support the improvement of flexibility through shallow and deep water exercise. Exercise participants are able to use the buoyant properties of water to decrease joint stress while gaining flexibility. Additional research needs to be conducted using various flexibility tests as well as training regimens of increased length.

Part II: Shallow and Deep Water Exercise Responses
Treadmill running is considered the ‘gold standard’ exercise modality to which all other modalities are compared. Studies comparing treadmill to other modalities such as cycling, simulated cross-country skiing, rowing, and stepping have shown treadmill running to elicit the highest energy expenditure and oxygen consumption (Thomas, Ziogas, Smith, Zhang, & Londeree, 1995; Zeni, Hoffman, & Clifford, 1996) . It therefore can be assumed that water exercise comparisons to treadmill running will have similar findings. However, the true relationship of water exercise to treadmill running (and other forms of land exercise) can only be determined through experimental research. Knowledge of the acute physiological responses of aquatic exercise programs helps the applied professional make correct decisions on safe and effective programming for participants. Part II of this aquatic review will summarize the responses to shallow and deep water exercise.
Comparisons of Submaximal Land and Water Exercise in Waist-To-Chest Deep Water
A pioneer aquatic investigation examined the oxygen consumption and heart rate responses of walking and jogging in waist deep water and on land with six males (21 - 42 yr) (Blanche, Evans, Cureton, & Purvis, 1978) . Water temperature was 30 degrees C (86°F) to 31 degrees C (88°F). In waist deep water, walking and jogging produced similar heart rate responses to land while oxygen consumption was higher in water. It was concluded that the water resistance in waist deep water while walking and jogging results in high levels of energy expenditure with relatively little strain on the lower extremities.
Hered et al. (1997) compared aquatic exercise using the arms and legs, and legs only, on land and in chest deep water at four different intensity levels with 12 females (mean = 20 yr). Results indicated that heart rates were lower in water than on land while oxygen consumption at 2 of the 4 intensities were significantly higher in water. Subjects incorporating both the arms and legs had the highest heart rates regardless of the environment (land or water). This study substantiates that adding the arms to leg exercise in chest deep water increases the energy expenditure cost of the aquatic activity.
One investigation studied the effect of walking on land and in water (at a matched cadence of 103 bpm), with and without an external elastic resistance belt, in ten male and eight female college-aged participants (Robert, Jones, & Bobo, 1996) . The elastic belt (tubing) allowed for more resistance to be applied to the arms and shoulders during exercise. Water temperature ranged from 22.2 degrees C (72°F) to 25.6 degrees C (78°F). Treadmill walking had significantly higher oxygen consumption and kilocalorie expenditure than matched exercise in chest-deep water. The resistance belt was not of sufficient magnitude to affect the oxygen cost or caloric cost of the exercise on land and in water.
Comparison of Aerobic Exercise on Land to Water
In a comparison of identical aerobic exercise routines on land and in water with ten female subjects (mean = 43 yr), land exercise produced significantly higher oxygen consumption results (Heberlein, Perez, Wygand, & Connor, 1987) . However, the cardiovascular stimulus for the hydroaerobics program was within ACSM guidelines for the improvement of cardiovascular endurance. Having the subjects perform the same exact aerobic exercise routines on land and water may have impaired the participant responses due to the varying effects of water density (800 times greater) compared to land.
Cassady and Nielsen (1992) evaluated heart rate and oxygen consumption of 40 subjects (20 males, 20 females, mean = 25 yr) performing upper extremity and lower extremity exercise on land and in water, at three different cadences. The oxygen consumption responses were greatest during water exercise, whereas heart rate, expressed as a percent of age-predicted heart rate maximum was highest on land, attributable in part to the hydrostatic pressure of water.
Maximal Intensity Land and Water Exercise Comparisons in Chest Deep Water
One investigation compared maximal oxygen consumption (VO2max), maximum heart rate (HRmax) and ratings of perceived exertion (RPE) of treadmill running to aquatic exercise (in chest deep water) with 19 males and 11 females (Hoeger, Hopkins, Barber, & Gibson, 1992) . The aquatic exercise consisted of arm and leg work which was gradually increased by speeding up the movement to attain maximal work output. Maximal treadmill exercise elicited a significantly higher response in VO2max, HRmax and RPE. This is not surprising since treadmill exercise has been shown to produce higher VO2max values when compared to other modalities (Thomas et al., 1995) .
Comparison of Bench Stepping on Land and in Water
Evans and Cureton (1996) compared oxygen consumption, heart rate and perceptual response of bench stepping on land and in chest-deep water. Ten women completed 5-minute trials of aqua bench stepping (29 steps/minutes) at three different bench heights (0, 7 in, 12.5 in) using a traditional stepping pattern and an arms and legs stepping pattern (water only). Water temperature varied between 29 degrees C (84°F) and 32 degrees C (90°F). Heart rates and oxygen consumption were lower in the water, although the perceived exertion response was very similar for stepping in water and on land. The added use of arms to legs increased oxygen consumption demands of the movement to 48%, 58%, and 78% of VO2peak, for the step heights 0, 7 in, and 12.5 in, respectively. Thus, bench stepping with the use of the arms in water meets ACSM guidelines for the improvement of aerobic capacity (50% to 85% VO2max).
Heart Rate and Oxygen Consumption of Shallow Water Exercise
Eckerson and Anderson (1992) explored the energy expenditure of shallow water aquatic exercise. In approximately 1 meter of water, 16 college females (20 yr) performed shallow water exercise routines. Maximal metabolic and cardiovascular data for the subjects was also obtained from land tests on a treadmill. When compared to treadmill effort, shallow water exercise resulted in mean heart rate responses that were 74% of heart rate reserve and 82% of HRmax, while VO2 was 48% of VO2max (minimally meeting ACSM guidelines). Subjects burned an average of 5.7 kilocalories per minute during the aquatic exercises.
Another investigation studied the effects of rhythmic aquatic calisthenics (stretching, jogging in place, modified lap swimming, simulated crawling, and treading water) on heart rate and oxygen consumption, at three different intensities (Vickery, Cureton, & Langstaff, 1983) . The researchers found heart rates of 70% to 77% and oxygen uptakes of 51% to 57% (meeting ACSM guidelines) of maximal values. The caloric expenditure ranged from 5.9 to 6.5 kilocalories per minute for the various programs.

Deep Water Running Studies
Treadmill Walking/Running vs. Deep Water Walking/Running
Coad et al. (1987) studied the energy costs of treadmill walking and running versus matched speeds of deep water walking and running with 14 subjects. Subjects wore wet vests while exercising in the water. Results indicated that deep water walking required significantly greater metabolic costs than treadmill walking. Deep water running and treadmill running were very similar in energy expenditure.
VO2 (L/min) HR (b/min) Kcal Expenditure
Treadmill walking .850 101 4.0
Treadmill running 2.35 163 11.8
Deep water walking 1.8 130 8.78
Deep water running 2.30 162 11.5
DeMaere et al. (1997) compared five-minutes trials of deep water running to treadmill running at 60% and 80% of VO2peak in eight cross-country runners. Deep water running and treadmill walking at similar intensities resulted in similar energy expenditure values.
VO2 (ml/kg/min) HR (b/min) Kcal Expenditure
Water 60% VO2peak 39.6 143 13.5
Treadmill 60% VO2peak 40.7 143 13.8
Water 80% VO2peak 54.9 172 18.9
Treadmill 80% VO2peak 55.4 173 19.2
Svedenhag and Seger (1992) compared running on land to vest-supported deep water running with 10 trained male runners (26 yr). Subjects ran at heart rates of 115, 130, 145, 155-160 bpm and also exercised to maximal exercise intensity. Maximal oxygen uptake (4.03 vs 4.60 l/min) and maximal heat rate (172 vs 188 bpm) was lower during water running. The authors suggest the lower maximal heart rates may be attributable to an increase in heart blood volumes, while the influence of different test procedures in the water vs. land may partially explain the differences in VO2max. RPE values were higher for deep water running as were the blood lactate concentrations at any given VO2. These responses may be due to a decreased blood flow in the legs during deep water running as well as the altered leg muscle activation patterns of deep water running.
An investigation by Glass, Wilson, Blessing and Miller (1995) compared the maximal physiological costs of deep water running to treadmill running using ten male and ten female subjects (26 yr). Treadmill running produced higher VO2 and heart rate values. However, heart rate was measured by palpation, and water temperatures were reported to be 24°C (75°F), which has been shown to be associated with a lowered exercise heart rate response. Treadmill running elicited higher metabolic training intensities than deep water running when equated for the same level of RPE. The authors suggested that due to the density of water, subjects utilized more anaerobic energy because of the increased challenge to the exercising muscles, and thus had lower VO2 and heart rate values. In addition, the use of the arms and legs against the water resistance contributed to higher lactate levels for deep water running as compared to treadmill running.
Frangolias, Rhodes, and Taunton (1996) compared the cardiovascular responses of maximal deep water running to treadmill running utilizing 22 endurance runners (8 female, 14 males, ages 21 to 35 yr) who were divided into experienced and inexperienced deep water running groups and given maximal exertion tests on the treadmill and in the water. Experienced deep water runners were classified as those doing at least 6 deep water running workouts per month for 6 months prior to the study. Results indicated that the more familiar subjects were with deep water running, the smaller the difference in maximal oxygen uptake values between water and land running. Experienced deep water runners had VO2max values on land and in water that were within 3.8 ml/kg/min whereas the difference in the inexperienced deep water runners was 10.3 ml/kg/min. Underwater video analysis revealed that inexperienced deep water runners were unable to maintain upright positions in the water and more likely to cup the water with their hands, propelling themselves slightly forward. Leg patterns of the inexperienced deep water runners adapted to a shorter stride cycle, similar to a swimming kick motion, which increased the contribution of the upper body. Maximal heart rate results indicated no significant differences in maximal heart rate in land vs. water in the experienced deep water runners. The researchers concluded that the more familiar individuals are with deep water running, the more closely matched the physiological responses of the two exercise mediums.
In another study using experienced deep water runners, Frangolias and Rhodes (1995) found higher maximal metabolic values on land compared to deep water running with 13 distance runners (21-35 yr). Experienced deep water runners were defined as those who incorporated at least 6 DWR workouts per month into their training program for six months prior to the study. Maximal VO2 and heart rate values were approximately 8% lower in water as compared to land. Also, lower ventilatory threshold (which is a marker for the body’€™s production of lactic acid) values were noted for DWR as compared to treadmill running at the same RPE and respiratory exchange ratio (the ratio of carbon dioxide produced and oxygen consumed) levels. However, when ventilatory threshold was expressed as a percentage of the respective DWR or treadmill VO2 values, there was no statistical difference. This suggests that factors dampening the effect of maximal effort also appear to be factors limiting VO2 at the ventilatory threshold.

The authors suggest that the differences observed in maximal values in land versus water are most likely related to hydrostatic responses, gravitational effects, and running styles in the different mediums. It is noted that during exercise in water there is a tendency for breathing frequency to be higher and tidal volume lower in submaximal (80% of VO2max) and maximal exercise (Sheldahl et al., 1987) . This suggests that the cost of breathing in DWR increases and a larger portion of oxygen is consumed by the respiratory muscles during water exercise as compared to land. This may function to limit the oxygen available to the leg muscles. Researchers also reported similar blood lactate responses during submaximal, maximal and recovery periods in land and water. This implies that variations in arm and leg actions (DWR technique) as well as the recruitment patterns in the deep water running that may limit oxygen consumption also contribute to the onset of blood lactate.
Michaud et al. (1995) compared the physiological, perceptual and metabolic responses of peak and moderate intensity deep water running to treadmill running with six trained male runners (mean = 25 yr). Peak oxygen consumption and heart rate were 12% and 8% greater for treadmill running than deep water running At similar relative and absolute exercise intensities, blood lactate and respiratory exchange ratio were significantly greater during deep water running. No significant difference was found in submaximal heart rate responses between trials. Subjects in this study were inexperienced DWR and received only three familiarization trials in deep water running.

Water temperature was maintained at approximately 29°C (84°F) to 30°C (86°F). Submaximal trials were 75% of treadmill VO2peak on treadmill (TM 75%), 70% of deep water running VO2peak in water (DW 70%), and 75% of treadmill VO2peak in water (TM 75%-W). Oxygen consumption at 75% of deep water running VO2peak was significantly lower than the other trials. No difference in heart rate occurred between trials. For both blood lactate and respiratory exchange levels, the water responses were significantly higher than land (TM 75%-W > DW 70% > TM 75%). At the same absolute exercise intensity, RPE values were higher in deep water running. The authors suggest that the mechanics of DWR are not as similar to land running as has been suggested by others.
Butts, Tucker and Smith (1991) investigated the maximal responses to treadmill and deep water running in 12 high school female cross country runners (mean = 15 yr). Subjects were taught DWR technique prior to testing, but had no previous experience with this form of training. Peak heart rate and oxygen consumption was higher on the treadmill than in water by 9% and 13%, respectively. The authors suggest the lower DWR metabolic responses may be attributable to a number of factors, including the cooling effect of the water temperature (29°C {84°F}), the hydrostatic forces exerted by water, the low body fat of the subjects (mean = 17.6%), and mechanical differences observed in deep water running due to the buoyancy effect of water. It was concluded that DWR provided numerous rehabilitation and training possibilities for athletes.
Maximal Gender Responses to Treadmill and Deep Water Running
Any investigation comparing maximal physiological responses between women and men is complicated by differences in body composition, physical size, and level of training. The larger percentage of body fat observed in women is a chief contributing factor to the lower cardiorespiratory observations (Pate & Kriska, 1984) . These differences in body composition may also facilitate buoyancy, possibly resulting in a reduced metabolic response in women when compared to men (making the water exercise more economical for women) (Brown, Chitwood, Beason, & McLemore, 1997) .
Butts, Tucker and Greening (1991) compared maximal physiological responses to treadmill running and deep water running in 12 trained men (mean = 20.6 yr) and 12 trained women (mean = 21.9 yr). Subjects were familiarized prior to testing with treadmill and deep water running exercise. Water temperature was 29°C (84°F). Men and women had significantly lower maximal VO2 and heart rate responses in water. The DWR VO2max values in water for men and women were 9% and 16% lower, respectively. The DWR maximal heart rate values in water for men and women were 5% lower. Respiratory exchange ratio was similar in both the water and on land. The authors concluded that the magnitude of these differences in water exercise and treadmill running is not different from that comparing treadmill running to other modalities and in no way precludes deep water running as an effective training technique.
Brown et al. (1997) explored the physiological differences to deep water running and treadmill running and differentiated them by gender with 12 untrained men (mean = 21 yr) and 12 untrained women (mean = 20 yr).

This investigation matched running cadences at a wider range of intensities to compare the two modalities. Subjects were familiarized to DWR with at least 2 DWR practice sessions prior to testing. Water temperature averaged 29.6°C (85°F). At all submaximal intensities, with running cadences matched in water and on land, deep water running resulted in higher VO2 responses. The authors concluded that at matched cadences in submaximal exercise, subjects were working harder during DWR. Heart rate was not significantly different between genders on land or in water (although heart rate on the treadmill was 6% and 10% higher than DWR for men and women, respectively). Men had significantly higher VO2max responses compared to women and treadmill VO2max values were 13% and 24% higher for men and women than in deep water running.

A very interesting finding of this study was that at matched running cadences, submaximal physiological responses for men and women were higher during DWR as compared to treadmill running.
Submaximal Energy Expenditure
An investigation with 8 male competitive runners (18 to 42 yr) running at a submaximal pace for 30 minutes showed deep water running incurred higher oxygen consumption values, respiratory exchange ratios, and RPE levels than normal treadmill running and road running (Richie &, 1991) . Heart rates were similar in the three experimental conditions. When subjects exercised at a self-selected ‘hard’ pace on the treadmill, metabolic values were higher than in deep water running. It was concluded that submaximal exercise can be sufficiently and effectively completed in deep water.
Differences in Deep Water and Treadmill Running Mechanics
It has been suggested that there is greater involvement of the anaerobic energy system during water exercise because of the additional recruitment of smaller muscle groups (Michaud et al., 1995) . Subjects have reported more fatigue in the arms, shoulders, hips, and legs during DWR, with potentially greater use of the upper body and less use of the lower body (Michaud et al., 1995) . The propulsion mechanics of the muscles in the legs when running are different than water, where the body is suspended and not working against gravity. In deep water running there is no weight-bearing and hence no push-off phase against a hard surface. Therefore, although deep water running mimics running on land, several important factors differentiate the two activities.

Table 4. Kilocalorie Expenditure
The following are some kilocalorie expenditure comparisons of different exercise modalities.
Exercise Mode Kilocalorie Expenditure
Aquatic exercise 5.7 - 6.5 kcal.min-1
Aerobic dance 6.2 - 6.6 kcal.min-1
Circuit training 5.1 - 6.1 kcal.min-1
Step aerobics 6.7 - 7.7 kcal.min-1
Running 11 min mile 8.0 kcal.min-1
Running 9 min mile 11.4 kcal.min-1
Walking normal pace 4.7 kcal.min-1
Deep water walking 8.8 kcal.min-1
Deep water running 11.5 kcal.min-1
Table 5. MET Values Table
Met levels are a unit of measurement frequently used to designate the energy costs of exercise programs. One MET equals 3.5 ml/kg/min. This table will provide MET data for various aquatic exercise programs. Due to variation in fitness levels of subjects and gender, these values are best used as approximations for the aquatic activity.
1st Author of Study & Yr Type of Aquatic Exercise Gender MET Levels
Cassady 1992 Upper extremity only Female 2.9-4.1
Cassady 1992 Upper extremity only Male 3.3-5.7
Cassady 1992 Lower extremity only Female 4.0-7.0
Cassady 1992 Lower extremity only Male 4.6-9.2
Echerson 1992 Aqua exercise in 1-meter of water Female 5.25
Vickery 1983 Waist-to-chest deep aqua calisthenics Female 6.7-8.3
Hered 1996 Chest deep aqua exercise with arms and legs Female 4.8-6.8
Evans 1996 Bench stepping, 7 inch step (no arms/with arms) Female 4.2/7.4
Evans 1996 Bench stepping, 12 inch step (no arms/with arms) Female 6.5/9.9
Kirby 1984 Running in chest deep water Female
& Male 7.1
Heberlein 1987 Aqua exercise in chest deep Female 5.4
Michaud 1995 Deep water running at 76% HRmax Male 11.0
Richie 1991 Deep water running at 83% HRmax Male 13.1

Summary Points
From this review of literature on the cardiovascular and energy expenditure responses to aquatic exercise, the following is a summary of findings:
Adding arms to leg exercise in chest deep water significantly increases the energy cost of the workout. This may equal or exceed matched exercise performed on land.
Water jogging and running in waist-deep water results in equal or even greater cardiovascular responses compared to similar exercise on land.
Aqua exercise routines can meet ACSM guidelines for the improvement of cardiorespiratory endurance. However, the ACSM guidelines for improvement of cardiovascular fitness may need to be adapted for aquatic training, since current standards prescribe only for land- based exercise.
Bench stepping exercise in water, using the arms, meets ACSM guidelines for the improvement of cardiorespiratory endurance.
Water exercise using elastic resistance with the upper body does not significantly increase energy expenditure.
Investigations have found the cardiorespiratory responses of deep water running to be less than, similar, and greater than treadmill running on land.
Blood lactate levels in deep water running have been shown to be higher and lower to land exercise which may reflect variations in arm and leg actions and exercise protocols.
Ratings of perceived exertion for DWR appear to be elevated due to higher blood lactate levels and upper extremity muscular fatigue.
The hydrostatic pressure and altered running style (due to different muscle activity patterns of DWR) contribute to a greater involvement of the anaerobic energy system during deep water running.
There is an increase in breathing frequency and cost of breathing during water exercise which leads to the respiratory muscles consuming more oxygen. This may function to limit the oxygen available for the legs.
The more familiar subjects are to DWR, the smaller the difference between VO2max values between land and water.
Exercise heart rate and oxygen consumption comparisons of teenage females in land and water exercise appear to result in similar responses to those seen in adults.

References:
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Arborelius, M., Balldin, U. I., Lilja, B., & Lundgren, C. E. G. (1972). Hemodynamic changes in man during immersion with the head above water. Aerospace Medicine, 43, 592-598.
Avellini, B. A., Shapiro, Y., & Pandolf, K. B. (1983). Cardio-respiratory physical training in water and on land. European Journal of Applied Physiology and Occupational Physiology, 50, 255-263.
Blanche, W., Evans, W., Cureton, K. J., & Purvis, J. W. (1978). Metabolic and circulatory responses to walking and jogging in water. Research Quarterly, 49, 442-449.
Brown, S. P., Chitwood, L. F., Beason, K. R., & McLemore, D. R. (1997). Deep water running physiologica responses: Gender differences at treadmill-matched walking/running cadences. Journal of Strength and Conditioning Research, 11, 107-114.
Bushman, B. A., Flynn, M. G., Andres, F. F., Lambert, C. P., Taylor, M. S., & Braun, W. A. (1997). Effect of 4 wk deep water run training on running performance. Medicine and Science in Sports and Exercise, 29, 694-699.
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