To simulate the effects of prolonged standing in the workplace on the leg muscles, we subjected mice to centrifugation for 6 wk. The absolute wet weight of leg muscles and internal organs of mice were measured after exposure to 3G by centrifugation for 6 wk and at 2 wk after removal of centrifugation. The weight of the soleus muscle (antigravity muscle) significantly increased after 6-wk exposure to centrifugation, but it decreased to its control weight 2 wk after removal of centrifugation. In contrast, the wet weights of the anterior tibial muscle, liver, and kidneys of mice centrifuged for 6 wk were significantly lower than those of the control mice; they had returned to control levels 2 wk after removal of centrifugation. It was therefore suggested that prolonged standing enlarged the leg muscles but its effect did not last for a long period of time after stopping prolonged standing. Western blot analysis of proteins extracted from the soleus muscle showed that vinculin and a-actinin in the centrifuged mice increased slightly, but there were no differences in the heat shock protein 70 (HSP70) and desmin levels between the centrifuged mice and control mice. No difference in HSP 70 suggested that muscle damage did not exist after 6 wk centrifugation.