The slow component of oxygen uptake during intense, sub-maximal exercise in man is associated with additional fibre recruitment

Publisher Website
Google Scholar
Abstract
Single muscle fibre metabolites and pulmonary oxygen uptake (V̇O2) were measured during moderate and intense, sub-maximal exercise to test the hypothesis that additional fibre recruitment is associated with the slow component of V̇O2. Seven healthy, male subjects performed 20 min moderate (MOD, ~50% of V̇O2,max) and intense (INT, ~80% V̇O2,max) cycling at 70 rpm. Glycogen content decreased significantly in type I and IIa fibres during INT, but only in type I fibres during MOD. During INT, creatine phosphate (CP) content decreased significantly both in types I and II fibres in the first 3 min (ΔCP: 16.0±2.7 and 16.8±4.7 mmol kg−1 d.w., respectively) and in the next 3 min (ΔCP: 16.2±4.9 and 25.7±6.7 mmol kg−1 d.w., respectively) with no further change from 6–20 min. CP content was below the pre-exercise level (mean−1 SD) in 11, 37, 70 and 74% of the type I fibres after 0, 3, 6 and 20 min of INT, respectively, and in 13, 45, 83 and 74% of the type II fibres. During INT, V̇O2 increased significantly by 6±1 and 4±1% in the periods 3–6 and 6–20 min, respectively (ΔV̇O2,(6−3min): 0.14±0.02 l min−1), whereas V̇O2 was unchanged from 3 to 20 min of MOD. Exponential fitting revealed a slow component of V̇O2 during INT that appeared after ~2.6 min and amounted to 0.24 l min−1. The present study demonstrates that additional type I and II fibres are recruited with time during intense sub-maximal exercise in temporal association with a significant slow component of V̇O2.