Surface electromyography of superficial back muscles in human children: Functions during vertical climbing and suspension and implications for the evolution of hominid bipedalism

Abstract

Surface electromyograms were taken of electrical activity in the trapezius, latissimus dorsi and caudal erector spinae muscles of human children as they elevated their superior extremities overhead and engaged in suspensory behaviors on a cargo net. Muscle activity patterns were determined and results were compared with electromyography (EMG) data derived from studies of juvenile pongid apes (Tuttle & Basmajian, 1976) in order to assess the problem of muscular economy and efficiency. Results from this preliminary investigation qualitatively verified Prost's (1980) hypothesis concerning the relative inefficiency of suspensory behaviors in man. Based on EMG data, these behaviors were less economical in Homo compared to pongid apes since selection presumably favored adaptations for efficient bipedalism at the expense of adaptations for efficacious climbing during the hominid evolutionary career. Some of these changes involved energy sparing regimes of superficial back muscle activity important for economical hanging and climbing. Relationships between the mode of attachment of the latissimus dorsi muscle and observed hominoid positional behaviors were elucidated within the context of lower back stability.