In addition to being a prerequisite for many activities of daily living, the ability to maintain steady upright standing is a relevant model to study sensorimotor integrative function. Upright standing requires managing multimodal sensory inputs to produce finely tuned motor output that can be adjusted to accommodate changes in standing conditions and environment. The sensory information used for postural control mainly arises from the vestibular system of the inner ear, vision, and proprioception. Proprioception (sense of body position and movement) encompasses signals from mechanoreceptors (proprioceptors) located in muscles, tendons, and joint capsules. There is general agreement that proprioception signals from leg muscles provide the primary source of information for postural control. This is because of their exquisite sensitivity to detect body sway during unperturbed upright standing that mainly results from variations in leg muscle length induced by rotations around the ankle joint. However, aging is associated with alterations of muscle spindles and their neural pathways, which induce a decrease in the sensitivity, acuity, and integration of the proprioceptive signal. These alterations promote changes in postural control that reduce its efficiency and thereby may have deleterious consequences for the functional independence of an individual. This narrative review provides an overview of how aging alters the proprioceptive signal from the legs and presents compelling evidence that these changes modify the neural control of upright standing.
Keywords: Ia afferents; balance; muscle spindles; proprioception; upright standing.