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 VO2max observed and VO2max 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 ± 0.05 l min−1). During the constant-load exercise, the VO2 SC (0.70 ± 0.22 l min−1) was correlated (r = 0.68, p < 0.01) to deoxyhemoglobin SC (2.94 ± 1.25 A U) 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.

Respiratory Physiology and Neurobiology