This was to test the stretch reflexes in your spinal cord, which resist muscle stretching to give you muscle tone to hold your body up against gravity for example, fast corrections after tripping.

The stretch reflex or myotatic reflex can prevent you from overstretching by contracting the muscle during a passive stretch. Think of it as a fast reaction response, hence "reflex." However ...

There was no interaction effect for grip strength following the three interventions. Conclusions: Acute WBV causes neural potentiation of the stretch reflex loop as shown by the improved ACMVJ and ...