Lowering of skin temperature decreases isokinetic maximal force production independent of core temperature.

Based on studies using maximal isometric contractions, it is suggested that fatigue may be elicited due to hyperthermia-induced impairments in central neuromuscular activation. We investigated the effects of passive hyperthermia on isokinetic maximal force production. Twenty young healthy males [peak oxygen uptake 52.9 (6.8) ml x kg(-1) min(-1), body fat 11 (5)%] were passively warmed in a hot (42 degrees C) water bath to rectal temperature ( T(re)) of 39.5 degrees C and then cooled back to 38.0 degrees C. At 0.5 degrees C intervals, they performed two maximal voluntary knee extensions each at 60, 120, and 240 s(-1). Peak torques at 37.5 degrees C were 168 (34), 145 (29), and 112 (17) N m for 60, 120, and 240 s(-1) contraction speeds, respectively, and 166 (38), 150 (31), and 119 (17) N m at T(re) of 39.5 degrees C. No significant differences in peak torque at any of the three contraction speeds were observed over the range 37.5-39.5 degrees C. Skin cooling, even with a warm core of 39.5 degrees C, immediately decreased peak torque [159 (42), 133 (34), 107 (22) N m at 60, 120, and 240 s(-1), respectively). We conclude that lowered skin temperature can impair isokinetic force production independent of core temperature.