Reflex inhibition during muscle fatigue in endurance-trained and sedentary individuals.
Reflex inhibition of the motoneuron pool following fatiguing contractions may be mediated by the build-up of byproducts of fatigue. Endurance training is accompanied by neuromuscular adaptations that would alter the production and/or clearance of metabolic substrates. The purpose of the study was to determine the extent of reflex inhibition during and after fatigue in endurance-trained individuals compared to sedentary controls. Subjects produced isometric ankle plantarflexion contractions at 30% of maximal voluntary contraction (MVC) until their MVC torque declined by 30%. H-reflexes were measured during a brief rest period every 3 min as well as superimposed upon the contraction every minute. Both groups of subjects experienced a similar amount of reflex inhibition by the end of the fatiguing protocol, although the endurance time was twice as long for the endurance-trained subjects. The endurance-trained subjects showed a greater reduction in H-reflex amplitude early in the fatiguing protocol compared to the sedentary subjects. These experiments have demonstrated that the neuromuscular processes associated with fatigue-related reflex inhibition must be multi-faceted and cannot be explained solely by small-diameter afferents responding to the byproducts of muscle contraction.
Walton
David M
DM
School of Physical Therapy, The University of Western Ontario, Elborn College, London, ON N6G 1H1, Canada.
Kuchinad
Raul A
RA
Ivanova
Tanya D
TD
Garland
S Jayne
SJ
D000328:Adult; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008019:Life Style; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010806:Physical Education and Training; D010807:Physical Endurance; D012420:Running; D013997:Time Factors