Strengths and limitations
It is a strength that we recruited a well-described clinical population in which improvement in exercise capacity is highly important. The adherence to the prescribed supervised exercise sessions was high and the drop-out was low, which is a strength. The sample size is relatively high in terms of a training study, but low in terms of differentiating between different genotype sub-groups, and hence our findings should be interpreted with caution due to potential statistical type II errors in the comparisons between genotype groups. Furthermore, the unequal genotype group sample sizes may represent a limitation, as this can negatively affect statistical power and Type I error rates