The effects of passive warming on muscle injury

This study investigated the effects of passive warming on the biomechanical properties of the musculotendi nous unit. Paired tibialis anterior (TA) and extensor digitorum longus (EDL) muscles in the rabbit hindlimb were passively heated to different temperatures and then subjected to controlled strain injury. The parame ters examined were: 1) percent increase in length to failure, 2) force to failure, 3) energy absorbed by the musculotendinous unit to failure, and 4) site of failure. Warmed (39°C ± 0.5°C) TA (P ≤ 0.01) and EDL (P ≤ 0.05) muscles achieved a greater increase in length from rest before failing than did their contralateral con trols at 35°C ± 0.5°C. In both the TA and EDL the force at failure was greater at 35°C than at 39°C, although the difference was significant for only the EDL (P ≤ 0.05). The energy absorbed (area beneath the length-tension curve) by both the TA and EDL was greater at 39°C, but these differences were not signif icant. All muscles failed at the distal musculotendinous junction. These data suggest that passive warming increases the extensibility of the musculotendinous unit and may thereby reduce its susceptibility to strain in jury.