ELECTROMYOGRAPHY OF BACK MUSCLES DURING QUADRUPEDAL AND BIPEDAL WALKING IN PRIMATES

Despite the extensive electromyographic research that has addressed li mb muscle function during primate quadrupedalism, the role of the back muscles in this locomotor behavior has remained undocumented. We repo rt here the results of an electromyographic (EMG) analysis of three in trinsic back muscles (multifidus, longissimus, and iliocostalis) in th e baboon (Papio anubis), chimpanzee (Pan troglodytes), and orangutan ( Pongo pygmaeus) during quadrupedal walking. The recruitment patterns o f these three back muscles are compared to those reported for the same muscles during nonprimate quadrupedalism. In addition, the function o f the back muscles during quadrupedalism and bipedalism in the two hom inoids is compared. Results indicate that the back muscles restrict tr unk movements during quadrupedalism by contracting with the touchdown of one or both feet, with more consistent activity associated with tou chdown of the contralateral foot. Moreover, despite reported differenc es in their gait preferences and forelimb muscle EMG patterns, primate s and nonprimate mammals recruit their back muscles in an essentially similar fashion during quadrupedal walking. These quadrupedal EMG patt erns also resemble those reported for chimpanzees, gibbons and humans (but not orangutans) walking bipedally. The fundamental similarity in back muscle function across species and locomotor behaviors is consist ent with other data pointing to conservatism in the evolution of the n eural control of tetrapod limb movement, but does not preclude the sug gestion (based on forelimb muscle EMG and spinal lesion studies) that some aspects of primate neural circuitry are unique. (C) 1994 Wiley-Li ss, Inc.