Passive stretching does not protect against acute contraction-induced injury in mouse EDL muscle.

A popular part of many athletes pre-game regime is to stretch. We examined whether a pre-injury stretching protocol could prevent acute contraction-induced injury. The in situ extensor digitorum longus (EDL) muscle of an anesthetized mouse (80 mg/kg intra-peritoneal) was used. Damage to the muscle from eccentric contraction-induced injury was quantified by the deficit in tetanic force production, and was not confounded by metabolic fatigue. The force deficits resulting from eccentric contractions alone (E) were compared with the force deficits resulting from a protocol that consisted of a stretch before the eccentric contractions (S + E). The pre-injury stretch was performed to 5% L0 strain, at a velocity of 0.5 mm/s. The muscle was held in the stretch position for 1 min, then slowly released. Eccentric contraction protocols (excursion > or = 24% L0) resulted in pronounced force deficits that increased with the excursion amplitude of the eccentric contraction. The eccentric contractions also resulted in an average right shift of 2 +/- 0.53% in the length-force relationship (t-test, P = 0.0001). The regression lines for the E (eccentric contraction only) and S + E (stretch and eccentric contractions) treatments did not differ from one another for either force deficit (ANCOVA, P = 0.82) or work deficit (ANCOVA, P = 0.12). Therefore, the pre-injury stretch protocol did not reduce the force deficit or the work deficit resulting from contraction-induced injury.