Fig. 1.

Correlation of FEV₁ and FEV₁/FVC versus peak oxygen consumption (VO₂ peak). Panel A is a scatter plot presenting the association of peak oxygen consumption (VO₂ peak – shown on y-axis) and forced expiratory volume in 1 s (FEV₁ – shown on x-axis). The plotted line is a line of best fit (estimated using restricted cubic splines), while the grey shaded zone represents its 95% confidence limits. Panel B is a scatter plot presenting the association of peak oxygen consumption (VO₂ peak – shown on y-axis) and the ratio of FEV₁ to forced vital capacity (FEV₁/FVC – shown on x-axis). The plotted line is a line of best fit (estimated using restricted cubic splines), while the grey shaded zone represents its 95% confidence limits.