Exercise in an aquatic environment may be an effective mode of therapy and training due to reduced impact forces. The purpose of this study was to compare the physiological responses of walking/running on a land treadmill with water treadmill responses at two different depths. Six subjects completed walking and running trials on both a land-based and a water-based treadmill. Water-based trials were completed in both thigh- and waist-deep water. Each trial was five minutes in duration. Oxygen uptake (VO2), heart rate (HR), respiratory exchange ratio (RER), stride frequency (SF), and the oxygen cost per stride (VO2/stride) were compared between the conditions using a two way ANOVA with repeated measures. Walking and running in water elevated VO2 (p < 0.02) and HR (p < 0.04) above land treadmill values. When running in waist-deep water, VO2 and HR failed to increase to the same extent as thigh-deep running. Stride frequency was similar between the three different depths during walking but lower in waist-deep water during running. VO2 tride was significantly higher (p < 0.01) in water-based walking and running compared to land-based values. Water-based walking and running elicited a greater physiological cost than land-based exercise, which can be attributed to the elevated cost of moving in water due to increased resistance. When running in waist-deep water, buoyancy may counter the resistance of the water and serve to lower the physiological cost of locomotion.
Keywords: underwater treadmill, energy cost, buoyancy, immersion, oxygen consumption