Running is a widely enjoyed aerobic exercise for many fitness enthusiasts and also is a common competitive event. In addition to track meets, there are hundreds of marathons and 5 and 10K runs providing competition for thousands of runners. The cardiorespiratory benefits of running are well documented, and along with swimming and cycling are the preferred aerobic exercises.
However, since running is weight bearing and frequently done on hard surfaces, running also is orthopedically stressful. It has been reported that the impact of the foot on the ground creates a force equal of 2 to 3 times greater than the runner's weight (1). For this reason alone, musculoskeletal injuries, particularly of the lower extremities, are very common.
Most of the lower extremity injuries sustained by a runner require rest and cessation of running for several weeks. The running enthusiast often has a conflict as to what he/she should do. The runner believes that rest and cessation of running will result in a loss of cardiorespiratory fitness and this has indeed been documented (2). Many exercisers who run, swim, or cycle are aware of the principle of specificity, i.e., training should consist of activities that are going to be performed. Most serious runners, because of the possibility of violating this principle of specificity, avoid using non-weight-bearing activities like cycling or swimming. Many times the impatience and paranoia about not running results in the enthusiast's return to running before injuries have completely healed. More often than not this results in re-injury, which dictates further need of rest and cessation of running.
The following discussion is focused on deep water running, however, much of this discussion is applicable to all water exercise.
In recent years, running in deep water has been used as a training alternative for injured runners, and because the motion is the running motion, runners assume that the principle of specificity is not compromised (3). This method of training has become popular with injured runners and is known as deep water running (DWR).
Many athletic facilities and some health clubs have recently built water tanks specifically to accommodate injured runners. These tanks are usually approximately 10 × 10 × 10 feet and are kept at a temperature of 29°C. If a tank is not available, the deep end of a swimming pool can be used. During DWR, a flotation device is usually used to keep the individual in a vertical position with the head above the water (this is termed supported DWR). Since there is no contact with the ground, the stressful impact of running on land is eliminated. Since heart rate (HR) is commonly used to determine exercise intensity, increasing the speed of the pumping action of the legs and arms while "running" in the water increases the HR and hence increases intensity of DWR and HR (4).
During DWR the arm and leg movements are almost the same as in running. Several studies have reported that if DWR is performed with adequate intensity cardiorespiratory fitness levels can be maintained and even improved.
In a study by Ed Eyestone M.S., and associates (5) 32 trained runners were divided into 3 groups, with each group training for 6 weeks either by water running, cycling, or treadmill running. The effects of the training were determined by comparing O2max values and 2-mile run performance time before and after the 6-week training period. The groups trained with the same frequency, duration, and intensity. The authors found that all subjects either maintained or improved their O2max, and there was no change in pre and post 2-mile run performance times. This indicated that DWR was able to maintain and even improve O2max and 2-mile run time.
Several studies have reported that at maximal workloads, maximal HR and O2 are lower during DWR when compared with treadmill running (TMR). It has been reported that the O2max for DWR is 83%-89% of treadmill values (6). In addition, maximal HRs during DWR were 89%-95% of maximal TMR HRs (7).
Based on these studies, it appears that exercise training intensity (determined from O2 and HR) in the water might be adjusted by lowering the values obtained on the land. In the health and fitness industry it is commonly agreed that during exercise in the water, maximal HRs and exercise HRs are lower than on land by approximately 10 beats per minute (6-8). Using this information, that the HR is lower in the water by 10 bpm, Timothy Quinn, Ph.D., and colleagues (9) devised a formula for HR to equate DWR and land exercise intensities. This suggested formula was 80% of heart rate reserve (HRR) − 10 bpm. HRR is maximum HR − resting HR (RHR). For a while after being published this formula was used fairly extensively by exercise leaders. So, for example, a 30 year old with a RHR of 70 bpm would work in the water at 86 bpm. In this example the individuals HRR is 120 bpm (Max HR 190 − RHR 70 = 120 bpm). Eighty percent of 120 is 96 bpm − 10 = 86 bpm. In the example above it seems obvious that a target HR of 86 bpm would be too low an intensity. Subsequent studies showed that this formula did not provide enough intensity to maintain O2max.
Although the comparisons of HR in the water and on land have been extensively studied, it is still unclear whether HR in water and on land differs when the workloads are identical. Workloads are difficult to equate and are usually done by measuring O2. Conflicting results in the studies to date indicate the need for more research. Jan I. Svedenhag, Ph.D., et al. (7) and Stan Ritchie, Ph.D., et al. (10) reported that for a given O2, the HR was lower in DWR than during TMR. In contrast, Thomas Michaud, Ph.D., et al. (11), John Mercer, Ph.D., and Randall Jensen, Ph.D., FACSM (12), and Jan DeMeare, Ph.D., FACSM, et al. (13) reported no significant difference in HR on land or in the water at equivalent submaximal O2.
In addition, to make the conflict worse, most of the research in DWR has been done on runners and not swimmers. There is no research comparing HR responses in competitive swimmers working on land and during DWR. Familiarity with the water may affect the HR and also may affect the rating of perceived exertion (RPE) while DWR.
In a study on HR and 3 different forms of exercise:running, cycling, and DWR (14), both runners and swimmers were used. To ensure that they were at the same fitness level and the same body composition MaxO2 and percent fat was determined. This study compared both the HRs and the RPEs in runners and swimmers during treadmill running, cycling, and DWR at 2 exercise intensities: 60% MaxO2 and 75% MaxO2. At 60% MaxO2 there was no significant difference in HRs or perceived exertion between TMR, DWR, and cycling for either the runners or the swimmers. However, at 75% MaxO2, HRs were significantly lower during DWR (22 bpm). The lower HRs during DWR may be the result of an increase in stroke volume or cardiac output because of the hydrostatic pressure of the water. No other studies have used swimmers as subjects during DWR studies. At the higher exercise intensity, 75% MaxO2, the runners, compared with the swimmers, also yielded a significantly lower RPE during running.
Since several studies have shown that swimmers have lower exercise HRs in the water compared with land, swimmers may need to adjust their training intensity in the water compared with land exercise.
Other factors such as water temperature and familiarity with the DWR technique should be considered when prescribing and monitoring DWR training intensity.
If one is to prescribe an exercise intensity for DWR or water exercise, since temperature has an affect on HR, the temperature of the water during the DWR should be the same as the temperature in the air when the HR for treadmill or track running is monitored.
Much of the research on HR in water and on land is done while swimming. Therefore, it should be noted that measurements, like HR, taken while swimming cannot always be compared with HRs during DWR since swimming is performed in a horizontal position with less hydrostatic pressure affecting the body, whereas DWR is performed in a near vertical position with more hydrostatic pressure affecting the body. The different positions in the water certainly can affect HR.
When evaluating DWR and running on land it should be also noted that although DWR and treadmill or track-running have similar movements, the muscle activity patterns may be different since there is no ground reaction force in DWR. Studies need to be conducted on the measurement of muscle activity patterns between treadmill running, cycling, and DWR through electromyography. It also would be valuable to measure and compare the differences in non-weight-bearing activities, cycling, and DWR.
However, in conclusion, DWR is a very adequate alternative method of cardiorespiratory training whether it is for an injured runner or as a different form of training. There are non-swimmers who could very successfully train in a pool through DWR. Likewise an overweight or obese individual who finds running orthopedically stressful can beneficially use DWR.
Condensed Version and Bottom Line
Running is a widely enjoyed aerobic exercise for many fitness enthusiasts and also is a common competitive event. However, since running is weight bearing and is frequently done on hard surfaces, it is orthopedically stressful creating a force equal to 2 to 3 times greater than the runner's weight. Because of this lower extremity injuries are very common. In recent years, DWR has been used as a training alternative for healthy and injured runners alike. During DWR, a floatation device is usually used to keep the individual in a vertical position with the head above water and the arm and leg movements are almost the same as in running. Several studies have reported that is DWR is performed with adequate intensity cardiorespiratory fitness levels can be maintained and even improved. DWR is a very adequate alternative method of cardiorespiratory training whether it is for an injured runner or as a different form of training. DWR also would be beneficial to an overweight or obese individual who finds running orthopedically stressful.
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2. Coyle, G.F., M.K. Hemmert, and A.R. Coggan. Effects of detraining on cardiovascular responses to exercise: role of blood volume. Journal of Applied Physiology
3. Wilber, R.L., R.J. Moffatt, B.E. Scott, et al. Influence of water run training on the maintenance of aerobic performance. Medicine & Science in Sports & Exercise®
4. Brennen, D. Water running with David Brennen
. Eugene, Oregon: Excel Sports Science, 1996.
5. Eyestone, E.D., G. Fellingham, J. George, et al. Effect of water running and cycling on maximum oxygen consumption and 2-mile run performance. The American Journal of Sports Medicine
6. Butts, N.K., M. Tucker, and C. Greening. Maximal responses to treadmill and deepwater running in high school female cross country runners. Research Quarterly for Exercise and Sport
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8. Butts, N.K., M. Tucker, and C. Greening. Physiologic responses to maximal treadmill and deep water running in men and women. The American Journal of Sports Medicine
9. Quinn, T.J., D.R. Sedory, and B.S. Fisher. Physiological effects of deep water running following a land based training program. Research Quarterly for Exercise and Sport
10. Ritchie, S.E., and W.G. Hopkins. The intensity of exercise in deep water. International Journal of Sports Medicine
11. Michaud, T.J., J. Rodriguez-Zayas, F.F. Andres, et al. Comparative exercise responses of deep water running and treadmill running. Journal of Strength and Conditioning Research
12. Mercer, J.A., and R.L. Jensen. Heart rates at equivalent submaximal levels of VO2 do not differ between deep water running and treadmill running. Journal of Strength and Conditioning Research
13. DeMeare, J.M., and B.C. Ruby. Effects of deep water and treadmill running on oxygen uptake and energy expenditure in seasonally trained cross country runners. Journal of Sports Medicine in Physical Fitness
14. Padilla, J. Comparison of heart rates between deep water running, treadmill running, and cycling. Unpublished thesis, University of Nevada, Las Vegas, 2001.