The purpose of this study was to investigate the characteristics of the ground reaction forces (GRF) during walking in water (WW).

Six males volunteered to participate in this study. Two different speed walkings, comfortable and the fastest one were tested to measure the GRF during WW.

The results revealed that the vertical component of GRF was decreased to about 25% of the body weight (BW), and the lateral medial GRF was decreased to less than 5% of BW during WW. The wave-form of anterior posterior GRF (APGRF) during WW was markedly different from that during land walking (LW). During the stance phase, APGRF on land showed two peaks corresponding to braking and driving forces, respectively. But in water, APGRF showed a single peak, which most probably corresponded to the driving force to propel the body forward.

These results clearly showed that impact force acting on lower joints at the time of heel contact was disappeared in water. However, the moments of lower joints for propelling the body forward could be increased dramatically, if the walking speed is increased in water.