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Lecture Notes

The third factor that influences flexibility is nervous system activity, or the signals that are sent to your central nervous system by proprioceptors in the muscles and in the tendons that attach muscles to bones. The stretch receptors, also called muscle spindles, are in the thick belly of the muscle and are very sensitive to quick and forceful stretching of the muscle. If this quick and forceful stretching occurs, as a protective mechanism to prevent overstretching, the spindles will send a signal to cause muscle contraction. So in order to prevent overstretching in the muscle, the muscle spindles cause that muscle contraction.