Metabolic costs and heart rate responses to treadmill walking in water at different depths and temperatures

Treadmill walking/jogging in water is a potentially useful therapeutic modality. Since energy costs of this activity are unknown, we compared oxygen consumption (VO2) of treadmill walking/jogging in water to a dry treadmill at speeds of 40.23 to 160.9 meters/min (m/m) in 13.4 m/m increments in 11 subjects. At speeds greater than or equal to 53.6 m/m, ankle depth, below knee, midthigh, and waist depth walking/jogging in water significantly elevated VO2 and heart rate (HR) above dry treadmill walking (P less than 0.05). At speeds greater than or equal to 134.1 m/m, VO2 of waist depth jogging was not significantly greater than dry jogging. These findings showed no gender specificity. Treadmill walking/jogging in waist depth water at temperatures of 30.5 degrees C and 36.1 degrees C was compared to dry treadmill walking in five subjects. The rate of increase of HR compared to VO2 was significantly greater at 30.5 degrees C than dry walking, and greater at 36.1 degrees C than 30.5 degrees C (P less than 0.05). Treadmill walking in water can double the oxygen cost of movement depending on the depth and speed, and the response to increasing speed is nonlinear. Water temperature affects the relationship of HR to VO2 at waist depth, suggesting that water temperature can add a significant thermal load to the cardiovascular system. Metabolic and cardiovascular demands of treadmill walking/jogging in water must be considered when using this modality since greater external work results at much lower speeds than on land.