Elevated Temperature Accelerates Recovery of Mouse and Human Skeletal Muscle Following Fatigue

• IntroductionThis study was designed to determine whether elevated muscle temperature allows muscles to recover their force or power more rapidly following fatigueMethodsIntact single fibers from mouse flexor digitorum brevis muscle were fatigued at 31˚C (70-Hz 350-ms tetani once every 10s until initial force decreased to 30%).  During a subsequent 2-hr recovery period, the fibers were perfused in Tyrode solution at either 31°C (physiological temperature) or 36°C and isometric force and cytoplasmic free [Ca2+] ([Ca2+]i) were measured during 30-Hz tetani evoked periodically.  In addition, seven human subjects performed fatiguing arm exercise consisting of 3 x 5min maximal effort arm cycling at 100 rpm followed by 4 x 15 min at an intensity of 50% of VO2peak. Then followed 2hr of recovery during which both arms were either heated or not heated at 5˚C above physiological temperatures using arm cuffs continuously perfused with temperature-regulated water; the order of heating vs. not heating was randomized between two visits. Intramuscular temperature was recorded with probes inserted 1.5 cm into the lateral head of the triceps brachii muscle. During the recovery period, subjects consumed 1.0 g/hr/kg body weight carbohydrates to support glycogen repletion. After recovery, the subjects repeated the 3 x 5 min time trials to evaluate the effect of the recovery intervention.ResultsRecovery from fatigue in mouse single fibers was dependent on muscle glycogen restoration since fibers perfused with glucose-free Tyrode did not recover contractile force (P<0.05). After 30 min of recovery, the tetanic [Ca2+]i was 107±10% and 92 ± 8% and the corresponding forces were 69±15% vs.49±14% of the initial values for the heated and non-heated muscles, respectively.  In seven human subjects, 2h of muscle heating also appeared to improve muscle recovery, leading to higher mean power output in the post-recovery arm cycling time trial than without muscle heating.DiscussionElevating muscle temperature by 5°C above physiological temperature accelerates recovery in mouse muscle in-vitro and in human skeletal muscle in-vivo and this appears to depend on faster muscle glycogen resynthesis following fatigue.

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MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Fysiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Physiology (hsv//eng)

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