Meeting Abstract
Human walking is characterized by coordinated out-of-phase movement of the arms and legs. Arm movements counteract angular momentum of the swinging legs about a vertical axis, conserving whole body momentum. Arm swing is likely produced passively by the momentum of the legs, but with active tuning by shoulder muscles. The aim of this study was to determine if the fundamental mechanisms of arm swing extends to bipedal non-human primates. We measured electromyographic activity patterns of the anterior deltoid, posterior deltoid, trapezius, triceps (long head), biceps (short head), pectoralis major, and latissimus dorsi muscles, and quantified the 3D kinematics of arm movement in two chimpanzee subjects during bipedal walking. Interlimb coordination was the same in chimpanzees as in humans, with the upper arm being extended at the ipsilateral heelstrike and flexed at the contralateral heelstrike. We found consistent phasic muscle activity occurring at ipsilateral heelstrike, in the latissimus dorsi for both subjects, and in the long head of triceps for one subject. We also found almost constant low-level activity for the posterior deltoid in both subjects. Therefore like humans forward swing in chimpanzees is likely passive while the backward swing may in part be produced by the latissimus dorsi. Most human studies have also observed extensor activity, but a few report additional low-level activity in anterior deltoid and biceps (< 3% maximum contraction). Humeral movement in the sagittal plane had 16-30 degrees amplitude with significant abduction and humeral rotation. This range overlaps with 27 degrees mean amplitude reported for humans in the sagittal plane. These results suggest that the basic pattern, and potentially function, of arm swing extends to facultatively bipedal chimpanzees. Funded by NSF grant BCS-0935321.
