Active stretching stimulates and prepares muscles for use during exercise.
Active stretches not only stretch the muscles and tissues, but prepares the muscles for the action by activating and warming them up or a stretch that requires you to retain a posture without any help other than the strength of your agonist's muscles is known as an active stretch..[1] Before describing the principles on which active stretching is based, the terms agonist and antagonist must be clarified.
The neuromechanisms conceptualized by Sir Charles Sherrington (1857 - 1956), “the philosopher of the nervous system”, as applied to active stretching are: Force applied to a muscle stimulates the muscle spindles which activate protective reflexes resulting in contraction of that muscle.
(Such as the knee jerk response of neurological testing procedures.)
While necessary for sports and ordinary motions, this protective reaction is counterproductive for stretching, i.e., lengthening muscles.