Fig. 9. Humeral retractor muscle recruitment profiles for individual chimpanzee subjects (A, chimpanzee #1; B, chimpanzee #2). Because of differences in forelimb posture between step-cycles when the overstriding hindlimb stepped inside the ipsilateral hand and ones where the foot landed outside the ipsilateral hand, outside-hand and inside-hand step-cycles were digitized separately [see (Larson and Stern, 1987) for additional details and explanations]. For caudal pectoralis major recordings, only samples of inside-hand steps were available for chimpanzee #2. See Fig. 3 caption for further explanation.