Figure 2. Representative COPD (A, B) and control (C, D) participants’ responses during the muscle oxidative capacity assessment.

Panels A and C show the TSI profiles during dynamic exercise, and intermittent arterial occlusion during recovery. Panels B and D show the calculated muscle ${\dot{\mathrm{V}}\mathrm{O}}_{\mathrm{2}}$ recovery profiles and kinetic fit (dashed line). The letters (a–e) are given to illustrate how the corresponding ${\mathrm{m}\dot{\mathrm{V}}\mathrm{O}}_{\mathrm{2}}$ value is derived from respective TSI negative slopes during intermittent occlusions. The grey area (EX) indicates the brief dynamic exercise. τ (s) is the ${\mathrm{m}\dot{\mathrm{V}}\mathrm{O}}_{\mathrm{2}}$ time constant determined by non-linear least-squares regression. k, is the rate constant, which is linearly related to muscle oxidative capacity (k = (1/τ).60, min⁻¹).