What does a knee-jerk response test have to do with your ankle sprain?

Almost everyone have this test done either in person or on television, the doctors takes out a small hammer and taps a spot just below the knee and the leg jerks forward. What does this test got anything to do with ankle sprains? The answer is stretch-reflexes.

Stretch-reflex is one of the key mechanism in proprioception; the body’s ability to sense its position in space relative to its other parts and the strength of effort in movement. In the case of an ankle sprain, muscles that are suppose to rein in an ankle that it rotating to much inward or outward either is firing too late, slowly or not firing at all, allowing the ankle to pass the ‘zone’ where tendons and ligaments experience too much stress.

How the body knows when ankle is going out of this ‘zone’ lies in a muscle spindle where the muscle attaches to the tendon (which in turn attaches to bone). This muscle spindle is extremely sensitive to stretch. When stimulated, it fires the motor neurons that are attached to the same muscle to contract. This reaction is very quick as it takes a much shorter route of going up the spinal cord and back, without going up to the brain for processing;  hence the automatic nature of the reflex.

Striking the tendon just below the knee cap, stimulates these muscles spindles in the tendon/muscle which causes the motor neurons to fire and ‘jerk’ the knee.

Injury can impair proprioception

Injury can reduce the effectiveness of an athlete’s proprioception, something that the athlete and coach may not be fully aware of even when rehabilitation seems complete. A team from the University of Pittsburgh looked at the role of the sensorimotor system as it relates to functional stability, joint injury and muscle fatigue of the shoulder and the restoration of functional stability after shoulder injury (1). They noted that to fully restore shoulder stability, deficits in mechanical stability, proprioception and neuromuscular control are needed.

If you have read our past articles, proprioception training is a key rehabilitation element is the recovery in a wide range of injuries involving the knee, shoulder and ankle.

Experiencing ankle pain? Click here to find out more about physiotherapy for ankle pain relief and how Core Concepts can help


  1. Journal of Athletic Training 2000; 35(3):351-363

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