An examination of neuromuscular and metabolic fatigue thresholds

This study examined the relationships among the physical working capacity at the fatigue threshold (PWC_FT), the power outputs associated with the gas exchange threshold (PGET) and the respiratory compensation point (PRCP), and critical power (CP) to identify possible physiological mechanisms underlying the onset of neuromuscular fatigue. Ten participants (mean ± SD age: 20 ± 1 years) performed a maximal incremental cycle ergometer test to determine the PWC_FT, PGET, and PRCP. CP was determined from the 3 min all-out test. The PWC_FT (197 ± 55 W), PRCP (212 ± 50 W), and CP (208 ± 63 W) were significantly greater than the PGET (168 ± 40 W), but there were no significant differences among the PWC_FT, PRCP, and CP. All thresholds were significantly inter-4 (r = 0.794–0.958). The 17% greater estimates for the PWC_FT than PGET were likely related to differences in the physiological mechanisms that underlie these fatigue thresholds, while the non-significant difference and high correlation between the PWC_FT and the PRCP suggested that hyperkalemia may underlie both thresholds. Furthermore, it is possible that the 5% lower estimate of the PWC_FT than CP could more accurately reflect the demarcation of the heavy from severe exercise intensity domains. (paper)