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The nervous system of mammals is very complex. For most major actions in the body the brain must decide what movement or action must be taken, the nerve impulses must be transmitted out of the brain, down the spinal cord and out to the intended receiver. Then when the action is carried out the impulse must return back the reverse pathway to tell the brain it was completed and start the next process. This is the path for any brain-controlled, conscious, impulses. Although it takes a lot of words to explain, it is really a very rapid process. There are many processes in the body that do not require direct thought to complete. The heart functions, breathing, metabolic processes, disease fighting and many other autonomic processes happen automatically in the body. The body uses signals to increase, decrease, or maintain many of these actions. If the carbon dioxide levels in the body begin to rise, the autonomic nervous system, through acid/base thermostats, calls for an increase in respiratory rate. Another automatic response by the nervous system is the reflex. The body reacts in a predetermined way based on specific stimulus. This may be a practiced response or a pre-programmed one. The stretch reflex is one of those responses. What is the Stretch Reflex? This is designed as a protective measure for the muscles, to prevent tearing. The muscle spindle is stretched and the impulse is also immediately received to contract the muscle, protecting it from being pulled forcefully or beyond a normal range. The synergistic muscles, those that produce the same movement, are also innervated when the stretch reflex is activated. This further strengthens the contraction and prevents injury. At the same time, the stretch reflex has an inhibitory aspect to the antagonist muscles. When the stretch reflex is activated the impulse is sent from the stretched muscle spindle and the motor neuron is split so that the signal to contract can be sent to the stretched muscle, while a signal to relax can be sent to the antagonist muscles. Without this inhibitory action, as soon as the stretched muscle began to contract the antagonist muscle would be stretched causing a stretch reflex in that one. Both muscles would end up contracting simultaneously. The stretch reflex is very important in posture. It helps maintain proper posturing because a slight lean to either side causes a stretch in the spinal, hip and leg muscles to the other side, which is quickly countered by the stretch reflex. This is a constant process of adjusting and maintaining. The body is constantly under push and pull forces from the outside, one of which is the force of gravity. Another example of the stretch reflex is the knee-jerk test performed by physicians. When the patellar tendon is tapped with a small hammer, or other device, it causes a slight stretch in the tendon, and consequently the quadriceps muscles. The result is a quick, although mild, contraction of the quadriceps muscles, resulting in a small kicking motion. Anatomy involved The motor neurons travel from the spinal cord to the muscle and back again in a continuous loop. Conscious movement comes from impulses in the brain travelling down the spinal cord, over this loop, and then back to the brain for processing. The stretch reflex skips the brain portion of the trip and follows the simple loop from muscle to spinal cord and back, making it a very rapid sequence.
The gamma efferent cells in the loop work to keep the muscles ready for the stretch reflex, even when inhibited or contracted. This is important because if the muscle is working against a load and shortening during contraction and an additional load is added, the muscle recognizes the stretch immediately and can compensate with a stronger contraction. This also protects the inhibited antagonist muscles from being injured from excessive stretching. What causes it? The stretch reflex can be activated by external forces (such as a load placed on the muscle) or internal forces (the motor neurons being stimulated from within.) An example of the former is a person holding an empty tray in their outstretched arm and then having a plate of food set on it. The stretch reflex would kick in to keep the tray at the same height and balanced. An example of the latter would be the shivering of a cold muscle. The motor neurons are stimulated from an internal "stretch" to warm the muscles. Any abrupt, forceful stretch on the muscle causes the stretch reflex to fire, in a healthy person. Delays in or absence of the stretch reflex are signs of possible neurological or neuromuscular compromise. What to Avoid When Stretching?
So, to avoid the stretch reflex and potential damage to your muscles and joints, avoid pain. Never push yourself beyond what is comfortable. Only stretch to the point where you can feel tension in your muscles. This way, you will avoid injury and get the maximum benefits from your stretching. Stretching is one of the most under-utilized techniques for improving athletic performance and getting rid of those annoying sports injuries. Don't make the mistake of thinking that something as simple as stretching won't be effective.
The Stretching Handbook & DVD will show you, step-by-step, how to perform each stretch EXACTLY! Plus, you'll learn the benefits of flexibility; the 7 critical rules for safe stretching; and how to stretch properly. Discover more about The Stretching Handbook & DVD here. If you enjoyed this issue of The Stretching & Sports Injury Report, please feel free to forward it to others, make it available for download from your site or post it on forums for others to read. Please make sure the following paragraph and URL are included. -----------------------------------------------------------
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