2018 Volume 24 Pages 37-45
In order to elucidate the function of the biarticular muscle described by Lombard’s paradox, the lever arm lengths of the long head of the biceps femoris and the gastrocnemius of a cadaver were investigated. The lever arm length of the long head of the biceps femoris was larger on the hip side than on the knee side even when the angle at the hip and knee joint changed, and became larger as the bending angle of the hip joint increased. The lever arm length of the gastrocnemius was larger on the foot side than on the knee side even when the knee and ankle joint angles changed, and increased as the plantar flexion angle increased. We designed a scaled wooden leg model based on the lower limb bone shape extracted from the cadaver, and attached rubbers imitating the long head of the biceps femoris and gastrocnemius in order to establish whether leg extension occurs. The biceps femoris long head rubber and gastrocnemius rubber both caused leg extension. The knee extension angular velocity of the gastrocnemius rubber was faster. These results suggest that the long head of the biceps femoris and gastrocnemius muscles act on leg extension in the standing position when the feet are fixed. The knee extension action of the gastrocnemius muscle is presumed to be strong based on data obtained on knee joint angular velocity from the wooden leg model.
