Respiratory and locomotor muscle implications on the VO₂ slow component and the VO₂ excess in young trained cyclists

We investigated the impact of ramp and constant-load exercise on (i) respiratory muscle fatigue and locomotor muscle oxygenation, (ii) their relationship with the excess VO₂ and VO₂ slow component (SC). Fourteen male cyclists performed two tests to exhaustion: an incremental ramp and a constant-load exercise with continuous monitoring of expired gases and oxygenation of the vastus lateralis muscle on two separate days. Maximal inspiratory (MIP) and expiratory (MEP) pressure measurements were taken at rest and post- exercise. The VO₂ excess represents the difference between VO_2max observed and VO_2max expected using linear equation between the VO₂ and the intensity before gas-exchange threshold. During the ramp exercise, MIP and MEP declined by 13±8 and 19±10%, respectively (p<0.05). MIP and MEP were not correlated to the excess VO₂ (0.09±0.05lmin^-1). During the constant-load exercise, the VO₂ SC (0.70±0.22lmin^-1) was correlated (r=0.68, p<0.01) to deoxyhemoglobin SC (2.94±1.25AU) but not to the excess VO₂ (r=0.30, p=0.2). Additionally, the significant decrease in MIP (20±9%) and MEP (23±11%) was correlated (r=0.55, p<0.05 and r=0.75, p<0.05, respectively) to the VO₂ SC. Our results show that respiratory muscle fatigue was correlated to the VO₂ SC in the constant-load exercise, whereas it was not correlated to the excess VO₂ in ramp exercise may be because of our small excess VO₂.