Fifty normal subjects (20 men, 30 women) were tested for maximal isometric contraction of the right knee extensor muscles while their hips were at angles of 100, 110, 120, and 130 degrees to the horizontal. The tested knee was positioned in 60 degrees of flexion. Knee-extensor force attained with the hip at 110, 120, and 130 degrees differed significantly greater than the knee force attained with the hip at 100 degrees. No significant difference in knee-extensor force was found when the hip angles varied between 110, 120, and 130 degrees. The findings were similar for both men and women. The results indicate a need for changes in the design of exercise units. Exercise units should provide for back stabilization with the hip positioned at varying angles and should be narrow enough to permit short subjects to grasp the sides of the unit.