Bipedal (Bp) locomotion is one of the most characteristic motor
behaviors in human beings. Innate quadrupedal (Qp) four-legged animals also
often walk bipedally. The walking posture, however, is significantly different
between the two. This suggests that although both have a potential to walk
bipedally, however, the human has a body scheme suitable for Bp locomotion,
probably its skeletal system. The skeletal system includes the lumbar lordosis,
sacral kyphosis, a round pelvis, a large femur neck angle, short feet, and so
on. To verify this hypothesis, we compared kinematic and EMG activities
between rats and humans during Qp and Bp locomotion on a treadmill belt. The
rat is a representative Qp animal, but it is able to acquire Bp walking
capability with motor learning. Although the mobile ranges of the hindlimb
joint are different during each locomotor pattern between rats and humans, both
showed replicable flexion and extension excursion patterns for
each joint depending on the locomotor phase. There are many phase-locked EMG
bursts between rats and humans during the same walking task and these are
observed in the proximal rather than the distal muscles. This suggests that
both rats and humans utilize similar neuronal systems for the elaboration of Qp
and Bp locomotion. It was interesting that both subjects showed more muscle
activities during non-natural locomotor patterns; Qp < Bp for rats and Bp
< Qp for humans. This indicates that rat Bp and human Qp walking need more effort
and we may be able to find its reason in their skeletal system.
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