Differences between Active and Passive Failure in Whole Skeletal Muscle

Extensive research has been performed examining eccentric contraction and related muscle injury. Only a few studies have examined muscle failure due to an imposed tissue strain. Those that have examined failure tend to investigate active muscle failure and define failure as complete tearing of the muscle. However, muscle damage is known to occur well before a tear is apparent, and failure may be better defined by a drop in force during stretch. Leonard et al. showed that isolated rabbit myofibrils fail (as defined by a drop in force during stretch) beyond actin-myosin overlap in both active and passive states; however, active myofibrils failed at much higher forces than passive ones. This study, carried out on frog (Rana pipiens) tibialis anterior muscles, was performed to see if this difference between actively and passively stretched myofibrils persisted in whole muscles.