 This study examined the effects of treadmill slope variation on external power output, PO, and propulsion technique reliability. It also assessed whether PO is related to propulsion technique. The results showed that PO variability accounted for up to 90% of the variability in propulsion technique variables when speed and wheelchair setup were kept constant. This suggests that small differences in PO between interventions may mask the effect of the intervention on propulsion technique. This article was authored by Sonya de Groot, Rachel E. Cowan, Megan K. McGillivray and others.