Abstract

An impairement of muscle energy metabolism has been suggested as a predisposing factor for, as well as a consequence of exertional heatstroke (EHS). 13 young men were investigated 6 months after a well-documented EHS using 31P-MRS. The relative concentrations of ATP, phosphocreatine (PCr), inorganic phosphate (Pi), phosphomonoesters (PME), and the intracellular pH (pHi) were determined at rest, during a graded standardized exercise protocol (360 active plantar flexions) and during recovery. Also the leg tissue blood flow was determined by venous occlusion plethysmography during the MRS procedure. 16 age-matched healthy male volunteers served as control group. In resting muscle, there were no significant differences between the groups as regards pHi, Pi/PCr, and ATP/PCr+Pi+PME ratios. During steady state exercise conditions, effective power outputs were similar for both groups at each level of exercise: 20, 35, and 50 of maximal voluntary contraction (MVC) of the calf muscle. No significant differences were shown between the two groups in Pi/PCr, pHi, or changes of leg blood flow at each level of exercise. At 50 MVC, Pi/PCr was 0.48+-0.08 vs 0.47+-0.05 (P=0.96), pHi was 6.94+-0.03 vs 6.99+-0.02, respectively (P=0.13). Finally, the rate of PCr resynthesis during recovery was not significantly different between the two groups; t1/2 PCr = 0.58+-0.07 vs 0.50+-0.05 min, respectively (P=0.35). Therefore, no evidence of an impairement of muscle energy mnetabolism was shown in the EHS group six months after EHS. Verf.-Referat