(a) Mitochondrial respiratory capacity in skeletal muscle. From protocols 1–3: control group, n = 17; NS group, n = 39; myalgic group, n = 23. ETF: control group, n = 17; NS group, n = 24; myalgic group, n = 9. (b) Activity of CS (marker of mitochondrial content) and β-hydroxy acyl-CoA dehydrogenase (marker of β-oxidation capacity). Control group, n = 14; NS group, n = 36; myalgic group, n = 21. (c) Mitochondrial intrinsic respiratory capacities (from protocols 1–3). Oxygen flux rates are normalized to mitochondrial content (CS activity). Control group, n = 14; NS group, n = 36; myalgic group, n = 20. (d) Maximal ROS production with oxygen flux through mitochondrial complex I and II (protocol 4). Control group, n = 15; NS group, n = 32; myalgic group, n = 12). CI_P, complex I–linked respiration; CII_P, complex II–linked respiration; CI+II_P, complex I+II–linked respiration; ETF, electron-transferring flavoprotein (lipid oxidation with 50 µM palmitoyl carnitine). ETS, electron transport system capacity, maximal uncoupled respiration; HAD, β-hydroxy acyl-CoA dehydrogenase; ROS pr O₂flux, maximal H₂O₂ production normalized to oxygen consumption (pmol O₂/s/mg) at the same substrate combination.*P < 0.05; **P < 0.01; ***P < 0.001; #P < 0.1.