The mechanisms underpinning the slow component of V̇O_2 in humans

Purpose When exercising above the lactic threshold (LT), the slow component of oxygen uptake ( V̇O_2sc ) appears, mainly ascribed to the progressive recruitment of Type II fibers. However, also the progressive decay of the economy of contraction may contribute to it. We investigated oxygen uptake ( V̇O_2 ) during isometric contractions clamping torque (T) or muscular activation to quantify the contributions of the two mechanisms. Methods We assessed for 7 min T of the leg extensors, net oxygen uptake ( V̇O_2net ) and root mean square (RMS) from vastus lateralis (VL) in 11 volunteers (21 ± 2 yy; 1.73 ± 0.11 m; 67 ± 14 kg) during cyclic isometric contractions (contraction/relaxation 5 s/5 s): (i) at 65