THE ROLE OF FATIGUE IN SUSCEPTIBILITY TO ACUTE MUSCLE STRAIN INJURY

We investigated the role of fatigue in muscle strain injuries using th e extensor digitorum longus muscles of 48 rabbits. The muscles of the rabbits were fatigued by 25% or 50% then stretched to failure and comp ared with the contralateral controls. Three rates of stretch were used . The force to muscle failure was reduced in the fatigued leg in all g roups (range, 93% to 97.4% compared with the controls), The change in muscle length in the fatigue groups was not different from the control s. The amount of energy absorbed in the fatigued muscle was 69.7% to 9 2% that of the energy absorbed in the control muscle. The lowest energ y absorption occurred in muscles that were more fatigued. In eight; ad ditional rabbits, fatigued extensor digitorum longus muscles were comp ared with submaximally stimulated muscles with the equivalent contract ile properties, and no difference was seen. Muscles subjected to strai ns are frequently injured under high-intensity eccentric loading condi tions. Under these conditions, muscles absorb energy and provide contr ol and regulation of limb movement. Our data showed that muscles are i njured at the same length, regardless of the effects of fatigue. Howev er, fatigued muscles are able to absorb less energy before reaching th e degree of stretch that causes injuries.