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Electromyography of pronators and supinators in great apes.

We obtained electromyographic recordings from the supinator, biceps brachii, pronator quadratus, and pronator teres muscles of a chimpanzee and a gorilla and from the supinator, pronator quadratus, and biceps brachii muscles of an orangutan as they stood and walked quadrupedally on horizontal and inclined surfaces, engaged in suspensory behavior, reached overhead, and manipulated a variety of foods and artifacts. In Pan troglodytes and Pan gorilla, as in Homo sapiens, the supinator muscle is the prime supinator, with the biceps brachii muscle serving to augment speed or force of supination. Primary of the pronator quadratus muscle over the pronator teres muscle during pronation is less clear in the African apes than in humans. Possibly, pongid radial curvature or forelimb elongation or both factors are related to the somewhat different patterns of activity that we observed in the pronator muscles of Pan versus those reported for Homo sapiens. In Pongo pygmaeus, as in P. troglodytes and P. gorilla, the pronator quadratus muscle acts as a pronator and the supinator muscle acts to supinate the hand at the radioulnar joints. The biceps brachii muscle is active at low levels as the orangutan supinates its hand with the elbow flexed.

Animals↗

Electromyography of back muscles during quadrupedal and bipedal walking in primates.

Despite the extensive electromyographic research that has addressed limb muscle function during primate quadrupedalism, the role of the back muscles in this locomotor behavior has remained undocumented. We report here the results of an electromyographic (EMG) analysis of three intrinsic back muscles (multifidus, longissimus, and iliocostalis) in the baboon (Papio anubis), chimpanzee (Pan troglodytes), and orangutan (Pongo pygmaeus) during quadrupedal walking. The recruitment patterns of these three back muscles are compared to those reported for the same muscles during nonprimate quadrupedalism. In addition, the function of the back muscles during quadrupedalism and bipedalism in the two hominoids is compared. Results indicate that the back muscles restrict trunk movements during quadrupedalism by contracting with the touchdown of one or both feet, with more consistent activity associated with touchdown of the contralateral foot. Moreover, despite reported differences in their gait preferences and forelimb muscle EMG patterns, primates and nonprimate mammals recruit their back muscles in an essentially similar fashion during quadrupedal walking. These quadrupedal EMG patterns 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 consistent with other data pointing to conservatism in the evolution of the neural control of tetrapod limb movement, but does not preclude the suggestion (based on forelimb muscle EMG and spinal lesion studies) that some aspects of primate neural circuitry are unique.

Animals↗

Diagnostic value of electromyography and muscle biopsy in arthrogryposis multiplex congenita.

Arthrogryposis multiplex congenita (AMC), a clinical syndrome characterized by multiple congenital joint contractures, frequently is caused by lesions in the peripheral nervous system. Two standard tests for the evaluation of the motor unit are nerve conduction studies/electromyography (NCS/EMG) and muscle biopsy. We reviewed the diagnostic value of these two studies in the evaluation of AMC over a 23-year period, analyzing 38 patients with AMC who had NCS/EMG, muscle biopsy, or both. Final diagnoses were classified as neurogenic (8 patients), myopathic (10 patients), "other" (12 patients), or unknown (8 patients). Neither test alone had consistently high sensitivities, positive predictive values, or specificities. However, when NCS/EMG and muscle biopsy were concordant for neurogenic or myopathic findings, they were more accurate than either test alone, especially for neurogenic diseases. Test results were most commonly discordant in patients with "other" or unknown diagnoses. These findings suggest that when the clinical evaluation indicates a specific syndromic, developmental, or exogenous cause, NCS/EMG and muscle biopsy are not helpful and may not need to be performed. When the history, examination, and genetic evaluation are unrevealing, NCS/EMG and muscle biopsy together provide valuable diagnostic information.

Arthrogryposis↗