We investigated the responses of intramuscular phosphate-linked metabolites and pH (as assessed by ³¹P-MRS) during intermittent high-intensity exercise protocols performed with different recovery-interval durations. Following estimation of the parameters of the power-duration relationship (i.e., CP and W') for severe-intensity constant-power exercise, eight male subjects completed three intermittent exercise protocols to exhaustion where periods of high-intensity exercise (60-s) were separated by different durations of passive recovery (18-s, 30-s and 48-s). The tolerable duration of exercise was 304 ± 68 s, 516 ± 142 s and 847 ± 240 s for the 18-s, 30-s and 48-s recovery protocols, respectively (P<0.05). The work done >CP (W_>CP) was significantly greater for all intermittent protocols compared to the subjects' W' and this difference became progressively greater as recovery-interval duration was increased. Similarly, the degree of intramuscular phosphocreatine restoration during recovery was greatest, intermediate and least for 48-s, 30-s and 18-s of recovery, respectively (P<0.05). The W_>CP in excess of W' increased with greater durations of recovery and this was correlated with the mean magnitude of muscle phosphocreatine reconstitution between work intervals (r = 0.61; P<0.01). During intermittent high-intensity exercise, recovery intervals allow intramuscular homeostasis to be restored, with the degree of restoration being related to the duration of the recovery interval. Consequently, the ability to perform W_>CP during intermittent high-intensity exercise and, therefore, exercise tolerance, increases in a predictable manner when recovery-interval duration is extended.