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First published online March 16, 2007
Journal of Experimental Biology 210, 1204-1215 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.002337

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Humeral retractor EMG during quadrupedal walking in primates

Susan G. Larson^* and Jack T. Stern, Jr

Department of Anatomical Sciences, Stony Brook University Medical Center, Stony Brook, NY 11794-8081, USA

View larger version (21K): [in this window] [in a new window]   Fig. 1. Schematic drawing of pectoralis, latissimus dorsi, and teres major in a primate (B, vervet monkey) compared to a nonprimate mammal (A, opossum). Although primates tend to have relatively longer limbs and a less crouched limb posture than other mammals of their size, the configuration of their humeral retractors does not differ substantially from that of other mammals. The asterisks indicate approximate positions of EMG electrodes. Opossum redrawn from Jenkins and Weijs (Jenkins and Weijs, 1979).

View larger version (72K): [in this window] [in a new window]   Fig. 2. Humeral retractor recruitment during quadrupedal walking across all taxa. Shaded areas represent the most consistent patterns of muscle use, that is, activity occurring 75% or more of the time in the samples of step cycles. Magnitudes of RMS values are shown as a percentage of the maximum level of activity observed during a recording session, with 100% of the maximum burst equal to the top of the y-axis. Step-cycle lengths have all been equalized for ease of comparisons. Each support phase begins with hand touchdown and ends with hand lift-off. Each swing phase begins with hand lift-off and ends with hand touchdown. Where there are multiple subjects for a single species, individual activity profiles were first scaled to their maximum bursts, and then the scaled RMS values were averaged to portray the species-specific profile. Colors refer to taxonomic groups: red, lemur species; blue, New World monkeys; orange, Old World monkeys; green, ape (chimpanzee). Lemurs are prosimians, a group that retains more primitive primate features; the other three groups are anthropoids or more advanced primates. *Opossum data is reproduced from Jenkins and Weijs (Jenkins and Weijs, 1979) for comparison.

View larger version (18K): [in this window] [in a new window]   Fig. 3. Humeral retractor muscle recruitment profiles for individual brown lemur (A1–3) and red-belly lemur (B1,2) subjects. As in Fig. 2, step-cycle lengths have all been equalized for ease of comparisons. Each support phase begins with hand touchdown and ends with hand lift-off. Each swing phase begins with hand lift-off and ends with hand touchdown. The magnitude of the RMS values are shown as a percentage of the maximum level of activity observed during a recording session, with 100% of the maximum burst equal to the top of the box along the y-axis. Blackened areas represent the most consistent activity, occurring in 75% or more of the step cycles, and the gray shaded areas represent more variable activity occurring at least 50% of the time.

View larger version (10K): [in this window] [in a new window]   Fig. 4. Humeral retractor muscle recruitment profiles for individual ring-tail lemur subjects (1–3). See Fig. 3 caption for further explanation.

View larger version (12K): [in this window] [in a new window]   Fig. 5. Humeral retractor muscle recruitment profiles for individual red-ruffed lemur subjects (1–3). See Fig. 3 caption for further explanation.

View larger version (11K): [in this window] [in a new window]   Fig. 6. Humeral retractor muscle recruitment profiles for individual spider monkey subjects (1–3). There were no successful recordings of caudal pectoralis major activity during walking for spider monkey #3. See Fig. 3 caption for further explanation.

View larger version (10K): [in this window] [in a new window]   Fig. 7. Humeral retractor muscle recruitment profiles for individual woolly monkey subjects (A,1,2) and the howler monkey (B). The only humeral retractor recording available for woolly monkey #2 was for latissimus dorsi. There was no successful recording of teres major activity for the howler monkey. See Fig. 3 caption for further explanation.

View larger version (15K): [in this window] [in a new window]   Fig. 8. Humeral retractor muscle recruitment profiles for individual vervet monkey subjects (A1–3) and for the patas monkey (B). See Fig. 3 caption for further explanation.

View larger version (16K): [in this window] [in a new window]   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.