Examining in situ changes to proprioceptive signals with increased muscle-tendon compliance

A major challenge in neuromechanics, particularly relevant to human health, is linking muscle-tendon (MT) morphology to proprioception. In anesthetized rats, we recorded intra-axonal sensory signals from active MT contractions. To modify the functional morphology, we physically added in-series springs. We demonstrated that as compliance increases, the gain of a muscle spindle declines. Therefore, conditions that alter MT compliance, like exercise, pregnancy, disease or aging, may modulate movements informed by sensory feedback.