Abstract Summary
We hypothesize that acto-myosin cross-bridge cycling dynamics govern history-dependence in muscle mechanics and muscle spindle afferent feedback that may impact human postural behaviors. Here we combine in vitro, in vivo, and in silico studies to determine movement amplitude thresholds affecting history-dependent features of muscle spindle firing rate and muscle stiffness. Our data show increased muscle short-range stiffness and sensory sensitivity to stretch during postural holds is preserved in the range of typical human postural sway. However, increases in sway amplitude, which are associated with increased fall risk, decreases muscle short-range stiffness and muscle spindle firing responses to stretch, impairing both intrinsic and muscle spindle-based sensorimotor reflexive mechanisms for postural stability.
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