Effect of temperature on muscle metabolism during submaximal exercise in humans

To study the effect of temperature on muscle metabolism during submaximal e xercise, six endurance-trained men had one thigh warmed and the other coole d for 40 min prior to exercise using water-perfused cuffs. One cuff was per fused with water at 50-55 degrees C (HL) with the other being perfused with water at 0 degrees C (CL). With the cuffs still in position, subjects perf ormed cycling exercise for 20 min at a work load corresponding to 70% (V)ov er dot (O2,peak) (where (V)over dot (O2,peak) is peak pulmonary oxygen upta ke) in comfortable ambient conditions (20-22 degrees C). Muscle biopsies we re obtained prior to and following exercise and forearm venous blood was co llected prior to and throughout the exercise period. Muscle temperature (T- mus) was not different prior to treatment, but treatment resulted in a larg e difference in pre-exercise T-mus (difference = 6.9 +/- 0.9 degrees C; P < 0.01). Although this difference was reduced following exercise, it was non etheless significant (difference = 0.4 +/- 0.1 degrees C; P < 0.05). Intram uscular [ATP] was not affected by either exercise or muscle temperature. [P hosphocreatine] decreased (P < 0.01) and [creatine] increased (P < 0.01) wi th exercise but were not different when comparing HL with CL. Muscle lactat e concentration was not different prior to treatment nor following exercise when comparing HL with CL. Muscle glycogen concentration was not different when comparing the trials before treatment, but the post exercise value wa s lower (P < 0.05) in HL compared with CL. Thus, net muscle glycogen use wa s greater during exercise with heating (208 +/- 23 vs. 118 +/- 22 mmol kg(- 1) for HL and CL, respectively; P < 0.05). These data demonstrate that musc le glycogen use is augmented by increases in intramuscular temperature desp ite no differences in high energy phosphagen metabolism being observed when comparing treatments. This suggests that the increase in carbohydrate util ization occurred as a direct effect of an elevated muscle temperature and w as not secondary to allosteric activation of enzymes mediated by a reduced ATP content.