A comparison of muscle activity and heart rate response during backward and forward walking on an underwater treadmill.

This investigation compared muscle activities and heart rate (HR) responses while subjects walked backward or forward in water, with and without a water current. Ten healthy males (23.5+/-1.4 years) volunteered for the study. Surface electromyography (EMG) was used to evaluate muscle activities while the subjects walked in water, immersed to the level of the xiphoid process. HR responses were monitored continuously by a telemetry method. A "Flowmill" was used for this study, which involves a treadmill at the base of a water flume. Measurement of maximal voluntary contraction (MVC) of each tested muscle was undertaken prior to gait analysis. The %MVCs obtained from the paraspinal muscles, vastus medialis and tibialis anterior were all significantly greater when walking backward than when walking forward, for every experimental condition (P<0.05). HR responses tended to be greater while walking backward than when walking forward, with a statistical significance at fast speed (P<0.05). In conclusion, walking backward in water resulted in significantly greater muscle activation of the paraspinal muscles, vastus medialis and tibialis anterior compared with walking forward in water. These findings may be helpful in developing water-based exercise programs.