Does high muscle temperature accentuate skeletal muscle injury from eccentric exercise?

Hyperthermia is suspected of accentuating skeletal muscle injury from novel exercise, but this has not been well studied. This study examined if high muscle temperatures alters skeletal muscle injury induced by eccentric exercise (ECC). Eight volunteers (age, 22.5 ± 4.1 year; height, 169.5 ± 10.8 cm; body mass, 76.2 ± 12.6 kg), serving as their own control, and who were not heat acclimatized, completed two elbow flexor ECC trials; in one trial the biceps were heated >40°C (HEAT) and in the other trial there was no heating (NON). HEAT was applied with shortwave diathermy (100 W) for 15 min immediately before the first ECC bout and for 2 min in between each bout. Individuals were followed for 10 days after each ECC session, with a 6‐week washout period between arms. The maximal voluntary isometric contraction decreased by 41 ± 17% and 46 ± 20% in the NON and HEAT trials, respectively. Bicep circumference increased by 0.07 ± 0.08 mm (4%, P = 0.04) and relaxed range of motion decreased by 11.5 ± 8.2° (30%, P < 0.001) in both trials. Serum creatine kinase peaked 72‐h following ECC (NON: 6289 ± 10407; HEAT: 5486 ± 6229 IU L(−1), 38‐fold increase, P < 0.01) as did serum myoglobin (NON: 362 ± 483; HEAT: 355 ± 373 μg L(−1), 13‐fold increase, P < 0.03). Plasma HSP 70 was higher (P < 0.02) in HEAT after 120‐h of recovery. There were no differences between treatments for plasma HSP27 and interleukins 1β, 6, and 10. The results indicate that >40°C muscle temperature does not alter skeletal muscle injury or functional impairments induced by novel ECC.