The metabolic transition speed between backward walking and running

Although the metabolic transition speed for forward exercise has already been determined, the walk–run transition speed for backward exercise has not been investigated before. The aim of this study was to determine the speed at which it becomes metabolically more efficient to run backwards than to walk backwards. Eighteen healthy volunteers, who successfully completed three backward exercise practice sessions, participated in the study. All subjects randomly performed two exercise tests: backward walking and backward running. Both protocols started at a treadmill speed of 5 km^.h⁻¹. Every minute the speed was increased by 0.5 km^.h⁻¹ until 8 km^.h⁻¹ was reached. Cardiorespiratory variables were continuously measured and blood lactate concentration [La] was determined every 2 min, using the Accusport lactate analyser. At each work load subjects rated their perceived exertion (RPE), using the Borg scale. There were no statistically significant differences in oxygen consumption, minute ventilation and heart rate between 6 and 7 km^.h⁻¹, for backward walking and backward running (P>0.05). There was no statistically significant difference in blood [La] between walking and running at 7.5 km^.h^-1 (P>0.05). According to the RPE values, subjects rated running at speeds less than 6 km^.h⁻¹ more difficult than walking at similar speeds. We conclude that the metabolic transition speed between backward walking and running is between 6 and 7 km^.h⁻¹, which is lower than the metabolic transition speed for forward locomotion (7.2–7.9 km^.h⁻¹).