Human muscle performance and PCr hydrolysis with varied inspired oxygen fractions: a31P-MRS study

Abstract

The purpose of this study was to use 31 P-magnetic resonance spectroscopy to examine the relationships among muscle PCr hydrolysis, intracellular H+concentration accumulation, and muscle performance during incremental exercise during the inspiration of gas mixtures containing different fractions of inspired O 2([Formula: see text]). We hypothesized that lower [Formula: see text]would result in a greater disruption of intracellular homeostasis at submaximal workloads and thereby initiate an earlier onset of fatigue. Six subjects performed plantar flexion exercise on three separate occasions with the only variable altered for each exercise bout being the [Formula: see text] (either 0.1, 0.21, or 1.00 O 2 in balance N 2). Work rate was increased (1-W increments starting at 0 W) every 2 min until exhaustion. Time to exhaustion (and thereby workload achieved) was significantly ( P < 0.05) greater as[Formula: see text] was increased. Muscle phosphocreatine (PCr) concentration, P i concentration, and pH at exhaustion were not significantly different among the three[Formula: see text] conditions. However, muscle PCr concentration and pH were significantly reduced at identical submaximal workloads (and thereby equivalent rates of respiration) above 4–5 W during the lowest[Formula: see text] condition compared with the other two [Formula: see text]conditions. These results demonstrate that exhaustion during all[Formula: see text] occurred when a particular intracellular environment was acheived and suggest that during the lowest [Formula: see text]condition, the greater PCr hydrolysis and intracellular acidosis at submaximal workloads may have contributed to the significantly earlier time to exhaustion.