Influence of muscle temperature during fatiguing work with the first dorsal interosseous muscle in man: a P-31-NMR spectroscopy study

Six healthy subjects rapidly lifted and lowered a small (250 g) weight with the first dorsal interosseous muscle (FDI) of one hand while the work perf ormed was recorded continuously until fatigue (defined as losing the abilit y to continue lifting). Work was recorded in units of chart recorder trace displacement from baseline (centimetres) as an isotonic transducer followed the movement of the weight. In all experiments, the temperature of the han d was first adjusted by immersion in a controlled-temperature water bath. I n the warmest condition, the skin surface temperature over the FDI was 30.5 (0.30)degrees C [mean (SE)]. After moderate cooling, this surface temperatu re was 21.5(0.16)degrees C. Cooling significantly reduced the time taken to reach fatigue and more than halved the work capacity. An intermediate degr ee of cooling was also used in four subjects, showing that most of the effe cts seen were changing incrementally. Before work, and at fatigue, intracel lular metabolic conditions in the FDI were studied by phosphorus nuclear ma gnetic resonance (P-31-NMR) spectroscopy? with occlusion of the blood flow maintained during measurements. The mean intracellular pH of the FDI was al so calculated. The changes observed were all consistent with the fact that intense work requires energy which must be derived largely from intracellul ar stores of phosphocreatine and glycogen. Less work made less demand upon reserves, and created lower concentrations of waste products and by-product s. The observations did not, however, allow us to explain why fatigue occur red at a particular point or why work capacity was reduced by cooling.