Effects of Fatiguing Isometric and Isotonic Exercise on Fractionated Patellar Tendon Reflex Components

Abstract

Despite intensive efforts to explain the mechanisms underlying neuromuscular fatigue, this phenomenon remains largely unexplained. The purpose of the present study was to examine fractionated reflex responses after local fatiguing isotonic and isometric muscular exercise of the quadriceps musculature. The fractionation procedure enables one to subdivide total reflex time into peripheral and central components. The central component (reflex latency) constitutes the time for the monosynaptic reflex arc. The peripheral component (reflex motor time) represents the time for muscular contraction. Twelve male university students were tested prior to and after severe isometric and isotonic exercise. Isometric exercise produced a strength decrement of 57%. The isotonic exercise task produced strength decreases of 35%. Although differential strength decrements were shown, both exercise types significantly (p < .01) lengthened total reflex time. Additionally, both reflex latency and reflex motor time were increased. These results suggest that severe muscular fatigue of either isometric or isotonic origin adversely affects total reflex time, especially the peripheral (muscular) component.