Stretch reflex conditioning in humans – implications for function

Abstract

Based on evidence from animal experiments and work on spinal cord injured patients, we have been developing a protocol to train healthy subjects to alter the size of their stretch reflex. As reflexes to a sudden stretch of a muscle mark an automated response it is conceivable that by this an increased contribution of afferent feedback to joint stiffness may occur. This may be particularly advantageous in recreational as well as elite athletes where joint stiffness and in particular its reduction induced by fatigue has been suggested as a possible risk factor leading to injury. We have to date trained eight subjects to upregulate their soleus reflex response of which six were successful. Data show that indeed afferent feedback is enhanced leading to increased stiffness around the ankle joint. Further, regulation of center of pressure (CoP) excursions when landing on one leg following a drop jump from a 30 cm height were substantially reduced. These results imply that ankle safety in injury prone situations may be improved and may help to reduce injury rates in sports.