Anatomically remote muscle contraction facilitates patellar tendon reflex reinforcement while mental activity does not: a within-participants experimental trial

Using a within-participants design, we investigated the relative effect of the JM and a successfully employed mental task (Stroop task) on the amplitude and temporal components of the patellar tendon reflex.We found that the addition of mental activity had no influence on the patellar tendon reflex parameters measured, while the JM provided facilitation (increased reflex amplitude, decreased total reflex time).The findings from this study support the view that the mechanism for the JM is a reduction in presynaptic inhibition of alpha motoneurons as it is influenced by physical and not mental activity.If a tendon reflex is not elicited during a neurological examination, a clinician may reattempt the procedure with reinforcement. One such reflex reinforcement technique is the Jendrassik maneuver (JM), which employs a voluntary anatomically remote muscle contraction concurrent with reflex elicitation [1]. The JM’s effect on amplitude and temporal components of the patellar tendon reflex has been demonstrated [2-8]. The underlying neurological mechanism of the JM remains elusive and is a source of debate.Two predominant but conflicting theories related to two different types of motoneurons have been proposed, and are feasible for scholarly discussion. One theory suggests that the JM acts via fusimotor activation. The fusimotor or gamma system consists of gamma motoneurons acting in response to changes detected in muscle spindle activity from Ia afferent fibres. The fusimotor system activity can be modulated by changes in the level of activity in either the mental, or physical state [9]. This was tested by comparison of microneurographic studies measuring muscle spindles in the tibialis anterior (TA) in a resting state compared to states of mental and physical action. They found that an enhanced sensitivity to stretch of muscle spindles compared to a rest condition occurred following either mental computation or voluntary fist clenching (which is an anatomically remote m