Why do muscles shake during stretching?
Muscles shake (produce a tremor) during stretching due to a reflex contraction (myotatic, lower motor neuron) and also a proprioceptive response (myotactic) that comes from the brain. As soon as a muscle is loaded, its receptors read the intensity and speed of the load. According to Stark (1999), in a stretching context, the load is the first stress placed on a muscle which results in the reflex contraction of that muscle. As soon as the receptors read “overload” the limb tends to shake. If you lessen the load, you also lessen the tremor. In manual or assisted, as well as self-stretches, the tremor is a sign to back off the barrier and work more gradually to achieve a normal resting length.
- Stark, Steven (1999). The stark reality of stretching. 4th ed. revised. Richmond, BC: Stark Reality Corp.