The influence of breathing mechanics on the development of the slow component of O2 uptake

We examined the influence of operational lung volumes and mean inspiratory flow on the amplitude of the slow component of O2 uptake (V˙O2SC) during constant-load cycling performed below and above the respiratory compensation threshold (RCT) in young (24 ± 1 yr), healthy individuals (n = 10). Subjects demonstrated a significantly greater rise in expiratory reserve volume (ERV) and mean inspiratory flow over the V˙O2SC period during exercise performed above compared with below the RCT (P < 0.05). Inspiratory reserve volume (IRV) was, on average, smaller for trials performed above relative to below the RCT (P < 0.05). The difference in the magnitudes of change in ERV and mean inspiratory flow, but not   IRV, were positively correlated with the increase in V˙O2SC amplitude between work rates (R2 = 0.86, P < 0.01). These findings suggest that dynamic hyperinflation and mean inspiratory flow (by increasing inspiratory resistive work) contribute to the development of the V˙O2SC, particularly when exercise is performed above the RCT.