An intrinsic mechanism to stabilize posture--joint-angle-dependent moment arms of the feline ankle muscles.
The neuromuscular system can use sensory feedback to regulate motion, but these feedback loops involve relatively long delays (50-100 ms) and may produce undesirable oscillations. However, stabilizing changes in muscle force can also be provided intrinsically (i.e. without feedback) by 2 properties of the muscle itself, its force-length and force-velocity relationships. We have discovered another intrinsically stabilizing mechanism in the musculoskeletal architecture of the cat ankle joint. Many of its muscles have their predominant moment arms about the adduction/abduction axis, with smaller moment arms for inversion/eversion and about the principal axis of motion, dorsiflexion/extension. The magnitudes of the moment arms in ab/adduction and in/eversion depend strongly on joint angle, increasing for positions away from neutral that lengthen the muscles. Thus, co-activation of agonist-antagonist pairs, known to occur in these muscles, would provide immediate stabilizing changes in torque when the ankle is perturbed away from neutral position.
Young
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RP
MRC Group in Sensory-Motor Physiology, Queen's University, Kingston, Ont., Canada.
Scott
S H
SH
Loeb
G E
GE
D000758:Anesthesia; D000818:Animals; D002415:Cats; D005246:Feedback / Q000502:physiology; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D009132:Muscles / Q000033:anatomy & histology / Q000502:physiology; D013643:Tarsus, Animal / Q000033:anatomy & histology / Q000502:physiology*; D013710:Tendons / Q000502:physiology