EFFECTS OF PROPHYLACTIC HEATING ON ECCENTRIC CONTRACTION-INDUCED INJURY IN MOUSE SKELETAL MUSCLE

Abstract

Prophylactic heat stress is known to induce stress proteins, e.g., heat shock protein-72 (HSP72), in muscle and to improve the recovery of cardiac and skeletal muscle from ischemia-reperfusion injury. PURPOSE The purpose of this study was to determine if prophylactic heat stress reduces the magnitude of the strength deficit following eccentric contraction-induced injury in mouse anterior crural muscles (i.e., primarily the tibialis anterior, TA). METHODS Hindlimbs of female ICR mice were immersed in a water bath either at 42 °C (heated group, n=8) or 34 °C (control group, n=7) for 30 minutes. Three hours after temperature induction, the left anterior crural muscles of mice performed 150 eccentric contractions in vivo. Peak isometric torques as a function of stimulation frequency (20–400 Hz) were measured immediately before and after injury, as well as at 3 and 7 d. RESULTS HSP72 levels were elevated 3 h after heat stress in TA muscles. There was no difference between groups for peak torque during the first eccentric contraction (6.4 ± 0.2 N mm) of the injury bout, as well as pre-injury peak isometric torques at frequencies >150 Hz. However, compared with the control group, the heated group exhibited significant reductions (11–54%) in pre-injury peak isometric torques at frequencies >150 Hz. In controls, peak isometric torques (20–400 Hz) were significantly reduced immediately (88–52%), 3 d (72–47%), and 7 d (53–26%) after injury. There were no differences (P=) between groups for peak isometric torques (20–400 Hz) during the first week after injury induction. CONCLUSION Prior heating of mouse hindlimbs did not protect anterior crural muscles against exercise-induced injury despite initial increases in HSP72 content.