2023-07-28 04:00:00
Proprioception is understood as the awareness of the position of one’s own body in space. Such awareness is fundamental to executing any sporting movement. Whatever the sport or movement, and to control muscle contraction, the central nervous system must be continuously informed via sensors regarding the results of its actions, as well as its position in space.
Such sensors are known as proprioceptors and provide information via feedback. Such afferent neural information is produced by sensory receptors as a result of movement. This information is then used as the basis for refining and improving the movement.
Various types of receptors provide proprioceptive input to the central nervous system. Muscle proprioceptors provide feedback information regarding muscle tension and length. The joints on the acceleration, angle, and direction of movement of the joints. The cutaneous ones with respect to the pressure on the skin.
For example, neck reflexes facilitate essential trunk and limb movements during somersaults, and gymnasts use strong head movements to control their twists. In all of them there are afferent sensory stimuli that ascend towards the central nervous system, as well as efferent motor stimuli that descend from the central nervous system towards the periphery.
The most complex and perhaps most important proprioceptor is the muscle spindle. Its structure is cylindrical, elongated, and thickened in its central part. Inside it there are two or more muscle fibers transformed and specialized to function as elongation mechanoreceptors. They are found throughout the entire muscle, but tend to be concentrated in its center. Each spindle is located within the muscle and parallel to the muscle fibers, and detects both the rate of change in its length and the total muscle length achieved.
Galileo (1564-1642) described motion in terms of rates of change as a function of unit time. A time rate of change of a quantity is the change in that quantity divided by time. This tells us how quickly something happens, or how much something changes in a certain amount of time.
The rates of change that describe the movement are three: 1.- speed (the rate at which a distance is covered in time); 2.- velocity (the rate at which a distance is traveled in time in a certain direction), and 3.- acceleration (the rate at which speed or velocity changes). Acceleration is complex because it represents a rate of change of another rate of change.
For example, when we stretch a muscle, the muscle spindles are also stretched and the afferent neuron whose peripheral axon terminates on the same spindle is stimulated. The afferent fiber passes to the spinal cord and synapses on the motor neurons that innervate that muscle. Since a stimulus is a detectable physical or chemical change in the environment of a sensory receptor, stimulation of the stretched muscle as a result of this stretch reflex causes the muscle to contract sufficiently to relieve the stretch.
Older people or those with weak quadriceps muscles take advantage of the muscle spindle by resting their hands on the center of their thighs when rising from a sitting position. Contraction of the quadriceps causes extension of the knee joint. Generated muscle tension is the force produced during muscle contraction by shortening of the sarcomeres, causing stretching and contraction of the elastic connective tissue and tendon of the muscle.
The act of pushing on the center of the thighs when standing up slightly stretches the quadriceps, stimulating the muscle spindles. The resulting stretch reflex aids in the contraction of the quadriceps muscles, and also helps the person to assume a standing position.
The stretch reflex is a monosynaptic reflex in which an afferent neuron originating from a muscle stretch receptor terminates directly on the efferent neuron innervating the same muscle to cause it to contract to counteract the stretch.
Athletes know how to use the muscle spindle and the stretch reflex to their advantage. To jump high, an athlete begins by bending the knees and squatting down. This action stretches the quadriceps muscles and increases the firing rate of the muscle spindles, thus triggering the stretch reflex that reinforces the contractile response of the quadriceps muscles. In this way the extensor muscles gain additional strength.
The same principle applies to the typical cleats seen in sprinting, the tennis backhand swing, and the golf swing. Such pre-stretches provide increased muscle arousal through reflex activity initiated by elongated muscle spindles.
Guillermo Laich de Koller
Doctor of medicine and surgery
1690528446
#Medicine #sports #science #Proprioception #muscle #spindle
