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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.
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