This article was written and reviewed by Gonca C, PHD, PT.
Throughout the human life span the functions of several physiological systems dramatically change, including proprioception.
Impaired proprioception leads to less accurate detection of body position changes increasing the risk of fall, and to abnormal joint biomechanics during functional activities so, over a period of time, degenerative joint disease may result. Altered neuromuscular control of the lower limb and consequently poor balance resulting from changes in the proprioceptive function could be related to the high incidence of harmful falls that occur in old age subjects.
Proprioception, was originally defined by Sherrington in 1906 as “the perception of joint and body movement as well as position of the body, or body segments, in space”. At present, proprioception can be defined as the cumulative neural input to the central nervous system from specialized nerve endings called mechanoreceptors. The mechanoreceptors are located in the joint, capsules, ligaments, muscles, tendons, and skin.
Proprioception is generally assessed by measuring both joint position sense (JPS) and the sense of limb movement. JPS determines the subject’s ability to comprehend a presented joint angle and then, once removed, actively or passively reproduce the same joint angle . Sense of limb movement determines detection of passive motion of the limb. Both components of proprioception are important for the generation of smooth and coordinated movements, maintenance of normal body posture, regulation of balance and postural control, and motor learning and relearning.
Motor coordination and balance are abilities that decline during the aging process, at least partially, by the deterioration of proprioception. The somatosensory system and, specifically, the proprioceptive system, are critically involved in the sensory control of balance. Colledge et al.  studied the relative contributions of vision, proprioception, and vestibular system to the balance in different age groups. They found that all age groups were more dependent on proprioception than on vision for the maintenance of balance. Thus, impaired proprioception could be a contributing factor to falls.
Decline in proprioception with aging could greatly influence balance, increasing the susceptibility to falls. Besides that, a decrease in proprioception could lead to abnormal joint biomechanics during functional activities such as walking so, over a period of time, degenerative joint disease may result.
Several studies showed a relationship between aging and decline in several aspects of proprioceptive sensitivity, namely a decrease in joint position sense and an increase in movement detection threshold. The lower limb, knee joint position sense [2,3], and ankle joint position sense  are negatively affected by aging. Similarly, in the upper limb, a decline in elbow and finger joint position sense was observed. Movement detection thresholds increased with advancing age, as shown by the results conducted in the knee, ankle, and metacarpophalangeal and metatarsophalangeal joints.
Proprioception vs. Kinesthesia
Presently, “kinesthesia” and “propriception” are used practically synonymously to indicate the capability to appraise the configuration and movements of an organism’s body parts. Kinesthesia can place a greater emphasis on motion. Some differentiate the kinesthetic sense from proprioception by excluding the sense of equilibrium or balance from kinesthesia. For example, an inner ear infection might degrade the sense of balance. This would degrade the proprioceptive sense, but not the kinesthetic sense. The affected individual would be able to walk, but only using the sense of sight to maintain balance.
Clinical aspect of proprioception is measured in tests that measure a subject’s ability to detect an externally imposed passive movement, or the ability to reposition a joint to a predetermined position. Proprioception is essentially a feedback mechanism; that is the body moves (or is moved) and then the information about this is returned to the brain, whereby subsequent adjustments could be made.
Kinesthesia is a key component in muscle memory and hand-eye coordination, and training can improve this sense. So many things that we do without thinking – such as walking, whether we do it correctly or not – is a kinesthetic experience based on proprioception, which provides the awareness of our joints and body in space.
Mechanisms of Proprioception Deterioration with Aging
Proprioception involves central and peripheral components. At the peripheral level, the construction of proprioception is based on the cumulative neural input from mechanoreceptors (articular, muscular, and cutaneous receptors).
The central component involves internal feedback loops that transmit information between and within sensory and motor areas. Advancing age causes a decline in proprioception involving both central and peripheral level. Recent studies suggest that proprioception decreases with aging is in part because of changes in muscle spindle function. In addition to that, advancing age leads to deficits in the processing of sensory input (myelin abnormalities, axonal atrophy, and declined nerve conduction velocity)  and neuromuscular performance decline.
At the central level, central somatosensory pathways conductive function is affected by normal aging. Aging induces progressive loss of the dendrite system in the motor cortex, losses in the number of neurons and receptors, and neurochemical changes in the brain.
Physical Activity in Proprioception Preservation During Aging
Peripheral level improvements in proprioception were linked to alterations in muscle spindle. There is no evidence that training changes the number of mechanoreceptors , but there is evidence that training induces morphological adaptations in the major mechanoreceptor involved in proprioception, the muscle spindle. Training can induce muscle spindle adaptations at a microlevel, the intrafusal muscle fibers may show some metabolic changes, and at a more macro level, the latency of the stretch reflex response decreases and the amplitude increases .
Physical activity improving muscle strength can improve proprioception. The improvement in muscle strength with exercise might yield better control of movement, which, as a consequence, could enhance joint proprioception under weight bearing conditions . (Closed kinetic chain exercises)
At a central level, physical activity might modify proprioception by modulating the mechanoreceptor gain and inducing plastic changes in the central nervous system. Muscle spindle is the one mechanoreceptor whose gain can be modulated by the central nervous system.
Repeated practice of a motor skill is thought to increase muscle spindle output, which could bring about plastic changes in the central nervous system, such as an increased strength of synaptic connections and/or structural changes in the organization and number of connections among neurons. Indeed, repetitive afferent inputs from the mechanoreceptors could modify the cortical maps of the body over time. Plastic changes in the cortex can be induced by repeated positioning of body and limb joints in specific spatial positions as demanded by exercise. Regular physical activity over time can increase cortical representation of the joints leading to enhanced joint proprioception.
There is evidence of proprioception deterioration with aging. Advancing age causes a decline in proprioception involving both central and peripheral level.
Regular physical activity seems to be a beneficial strategy to preserve proprioception and prevent falls among older subjects. Some studies have demonstrated that the regular physical activity can attenuate age-related decline in proprioception.
Strengthening exercises (both open and closed kinetic chain), balance training, weight bearing conditions, Yoga and Tai Chi can improve proprioception.
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