This paper studies whether non-separabilities between consumption and leisure may help to explain the observed persistence in GNP growth. We consider an extended version of Lucas's (1988) human capital investment model that includes labour adjustment costs and compare its performance under different utility specifications with different degrees of complementarity and substitutability between consumption and leisure. We find that when consumption and leisure are complements the model succeeds in matching not only the autocorrelation of output growth but also the important trend-reverting component found in US data. These results hold even if low adjustment costs of labour are considered. Hence, we conclude that an arguably simple margin not considered conventionally can provide useful insights into observed business cycle patterns.