The influence of chair height on lower limb mechanics during rising.

The mechanics of the lower limb were analyzed in young, adult normal subjects when rising from a seated position. Limb mechanics were described in terms of flexion-extension motion and moments at the hip, knee and ankle while rising from four seat heights corresponding to 65, 80, 100, and 115% of the subject's knee joint height. The results indicate that the maximum moment tending to flex the hip joint was higher than that occurring at the knee or ankle. The magnitude of the maximum flexion moment at the hip was not substantially influenced by chair height, changing by less than 12% between the highest and lowest chair heights. Conversely, the maximum knee flexion moments were found to be highly dependent on chair height and nearly doubled from the highest to the lowest position. The magnitude of the moments at the ankle did not change with chair height and were significantly lower than the magnitude of the moments found during normal walking. The magnitude of motion and moments at the hip were greater during chair-rising than during stair-climbing or walking. The range of motion required at the knee for the lower chair heights was also greater than was reported during stair-climbing studies. Thus, the combination of moments in joint angles during chair-rising are unique among common activities of daily living and should be considered in chair selection as well as in the guidelines for prosthetic devices.