Skeletal muscle mitochondrial correlates of critical power and<i> </i>W' in healthy active individuals

<p dir="ltr">The asymptote (critical power; CP) and curvature constant (<i>W</i>') of the hyperbolic power–duration relationship can predict performance within the severe-intensity exercise domain. However, the extent to which these parameters relate to skeletal muscle mitochondrial content and respiratory function is not known. Fifteen males (peak O2 uptake, 52.2 ± 8.7 mL kg⁻¹ min⁻¹; peak work rate, 366 ± 40 W; and gas exchange threshold, 162 ± 41 W) performed three to five constant-load tests to task failure for the determination of CP (246 ± 44 W) and <i>W</i>' (18.6 ± 4.1 kJ). Skeletal muscle biopsies were obtained from the vastus lateralis to determine citrate synthase (CS) activity, as a marker of mitochondrial content, and the ADP-stimulated respiration (_P) and maximal electron transfer (_E) through mitochondrial complexes (C) I–IV. The CP was positively correlated with CS activity (absolute CP,<i> r</i> = 0.881, P < 0.001; relative CP, <i>r</i> = 0.751, P = 0.001). The <i>W</i>' was not correlated with CS activity (<i>P</i> > 0.05). Relative CP was positively correlated with mass-corrected CI + II_E (<i>r</i> = 0.659, <i>P</i> = 0.038), with absolute CP being inversely correlated with CS activity-corrected CIV_E (<i>r</i> = −0.701,<i> P</i> = 0.024). Relative <i>W</i>' was positively correlated with CS activity-corrected CI + II_P (<i>r</i> = 0.713, <i>P</i> = 0.021) and the phosphorylation control ratio (<i>r</i> = 0.661, <i>P</i> = 0.038). There were no further correlations between CP or <i>W</i>' and mitochondrial respiratory variables. These findings support the assertion that skeletal muscle mitochondrial oxidative capacity is positively associated with CP and that this relationship is strongly determined by mitochondrial content.