Neuromuscular fatigue during repeated exhaustive submaximal static contractions of knee extensor muscles in endurance-trained, power-trained and untrained men

The neural and muscular changes during fatigue produced in repeated submaxi mal static contractions of knee extensors were measured. Three groups of di fferently adapted male subjects (power-trained, endurance-trained and untra ined, 15 in each) performed the exercise that consisted of 10 trials of sub maximal static contractions at the level of 40% of maximal voluntary contra ction (MVC) force till exhaustion with the inter-trial rest intervals of 1 min. MVC force, reaction time and patellar reflex time components before an d after the fatiguing exercise and following 5, 10 and 15 min of recovery w ere recorded. Endurance-trained athletes had a significantly longer holding times for all the 10 trials compared with power-trained athletes and untra ined subjects. However, no significant differences in static endurance betw een power-trained athletes and untrained subjects were noted. The fatigue t est significantly prolonged the time between onset of electrical and mechan ical activity (electromechanical delay) in voluntary and reflex contraction s. The electromechanical delay in voluntary contraction condition for power -trained and untrained subjects and in reflex condition for endurance-train ed subjects had not recovered 15 min after cessation of exercise. No signif icant changes in the central component of visual reaction time (premotor ti me of MVC) and latency of patellar reflex were noted after fatiguing static exercise. It is concluded, that in this type of exercise the fatigue devel opment may be largely owing to muscle contractile failure.