Telemetered electromyography of flexor digitorum profundus and flexor digitorum superficialis in Pan troglodytes and implications for interpretation of the O. H. 7 hand.

The importance of knuckle-walking in the locomotor repertoire of African apes raises the possibility that the long digital flexors may be specially adapted more to meet the demands of ground quadrupedalism than those of suspension. To investigate this possibiltiy, the activities of the flexor digitorum superficialis and flexor digitorum profundus were studied by means of telemetered electromyography in three chimpanzees. Results clearly indicate that the fasciculi of the muscles to digits bearing weight in knuckle-walking are not called upon to contract in quadrupedal postures or in slow and moderately fast quadrupedal locomotion except to help clear the fingers from the ground as the forelimb begins its recovery stroke. At the most rapid speeds, a slight to moderate level of activity sometimes occurs in the latter half of stance phase. The long digital flexors display maximum and sustained activity during suspension. It is concluded that any role for these muscles in maintenance of stability at the metacarpophalangeal joints during knuckle-walking must be predominantly passive. Prominent markings for insertions of these muscles in a fossil hand (such as O.H. 7) suggest use of the forelimb in suspensory climbing behaviors.