The Potential for the Metatarsophalangeal Joint Angle to Modulate Maximum Isometric Ankle Plantar Flexion Moments

The force-generating capacity of the ankle plantar flexor muscles is known to be influenced by both ankle and knee joint angles, but the metatarsophalangeal (MTP) joint may also affect these muscles. This effect may arise as 2 ankle plantar flexors, the flexor hallucis longus and the flexor digitorum longus, cross the MTP joint. It was the purpose of this study to determine the influence of the MTP joint on maximum voluntary isometric plantar flexor moments. Maximum isometric ankle plantar flexion moments were measured for 8 subjects with the MTP joint in either neutral or fully dorsiflexed position while the angles of the knee joint (90° flexion or fully extended) and ankle joint (4 angles) were systematically varied, giving 16 sets of joint configurations. There was no significant effect of the MTP joint angle on the maximum plantar flexion moment (P = .41), but both the ankle and knee joint angles had a significant effect (P < .001). During the stance phase of human gait, the MTP joint angle changes. The results of this study suggest that MTP orientation changes have no implications for the length-determined contributions of the flexor hallucis longus and flexor digitorum longus to the ankle plantar flexion moment.