THERMAL EFFECTS ON SKELETAL-MUSCLE TENSILE BEHAVIOR

The effect of temperature on the mechanical failure properties of rabb it skeletal muscle (tibialis anterior and extensor digitorum longus) w as examined. For all tests, one leg was maintained at 25-degrees-C and the contralateral leg at 40-degrees-C. Muscles were pulled to failure according to assignment into one of three groups: 1) passive failure at 10 cm/sec, 2) passive failure at 1 cm/sec, or 3) active (muscle is stimulated to contract as it is pulled) failure at 10 cm/sec. Load to failure was higher in the cold muscle for all groups tested. Total def ormation was the same except in Group 1, when the warm muscle had a gr eater deformation. Energy absorbed before failure was greater in the c old muscle in Groups 2 and 3. Stiffness was higher in cold muscles for all muscles except the extensor digitorum longus in Group 1. In this study, temperature had a significant effect on the tensile properties; these thermal effects were dependent on both loading rate and contrac tile state. Comparing loading rates, warm muscle tested at 10 cm/sec h ad higher failure loads than that tested at 1 cm/sec. Comparing stimul ated versus unstimulated muscle (Group 1 versus Group 3), the stimulat ed tibialis anterior muscle absorbed more energy than unstimulated one s. Stimulated extensor digitorum longus muscles had higher failure loa ds, absorbed more energy, and were stiffer than nonstimulated muscles. This study offers experimental data to support the theory that warmin g muscles can aid in injury prevention and improvement in athletic per formance.