Exercise-induced neuromuscular dysfunction under reflex conditions

The purpose of this research was to describe further the effects of exercis e-induced muscle damage on reflex sensitivity. The subjects were eight phys ically active, but untrained males, between the ages of is and 29 years. Th e effects of eccentric and concentric exercise on patellar tendon reflex re sponses were determined. The 8 week experiment consisted of two, 5 day, tes t protocols with a 6 week wash-out period between test protocols. Each 5 da y test protocol consisted of the following six test sessions: (1) day 1 - b aseline, (2) day 2 - baseline, (3) day 2 - immediate post-exercise, and (4- 6) days 3-5: 24, 48, and 72 h post-exercise. On day 2, the subjects made ei ther 100 fatiguing concentric or eccentric isotonic contractions using the right leg at 75% of the corresponding repetition maximum values. During eac h test session, the electromyogram (EMG) and force-time characteristics of basic and conditioned patellar tendon reflex responses were measured. The r eflex amplitudes of basic and conditioned patellar tendon reflex responses were decreased following fatiguing concentric exercise. There were no immed iate effects of fatiguing eccentric exercise on the basic and conditioned p atellar tendon reflex responses, but the EMG amplitudes of these reflex res ponses were reduced on the days following eccentric exercise. The amount of conditioned patellar tendon reflex facilitation was decreased following th e concentric exercise protocol and at 48 h post-eccentric exercise. Our con ditioned reflex data suggest that post-exercise changes to the physiologica l mechanisms that modulate the recruitment gain of the;I-motoneuron pool ma y depend upon the type of fatiguing exercise.