Oxygen Uptake and Lactate Kinetics in Patients with Chronic Obstructive Pulmonary Disease during Heavy Intensity...

Oxygen uptake slow component ([Formula: see text]_sc) is associated with lactate accumulation, likely a contribution of poorly oxidative muscle fibers. We aimed to test the hypothesis that higher muscle tension during slow pedaling rates would yield more prominent [Formula: see text]_sc in healthy subjects, but not in COPD patients. Eight severe COPD patients and 8 age-matched healthy individuals performed 4 rest-heavy exercise transitions at 40 and 80 RPM. Work rates at the two cadences were balanced. Venous blood was sampled for measurement of lactate concentration at rest and every 2 minutes until the end of exercise. [Formula: see text] kinetics were analyzed utilizing nonlinear regression. [Formula: see text] phase II amplitudes at the two cadences were similar in both groups. In healthy individuals, [Formula: see text]_sc was steeper at 40 than 80 RPM (46.6 ± 12.0 vs. 29.5 ± 11.7 mL/min², p = 0.002) but not in COPD patients (16.2 ± 14.7 vs. 13.3 ± 7.6 mL/min²). End-exercise lactate concentration did not differ between cadences in either group. In healthy individuals, greater slow-cadence [Formula: see text]_sc seems likely related to oxidative muscle fiber recruitment at higher muscular tension. COPD patients, known to have fast-twitch fiber predominance, might be unable to recruit oxidative fibers at high muscle tension, blunting [Formula: see text]_sc response.