Faster Stepping Cadence Partially Explains the Higher Metabolic Cost of Walking Among Females Versus Males.

The metabolic cost of walking (MCOW), or oxygen uptake normalized to distance, provides information on the energy expended during movement. There are conflicting reports as to whether sex differences in MCOW exist, with scarce evidence investigating factors that explain potential sex differences. This study 1) tested the hypothesis that females exhibit a higher MCOW than males, 2) determined whether normalizing to stepping cadence ameliorates the hypothesized sex difference and 3) explored whether more habitual daily steps and time in intensity-related physical activity, and less sedentary time were associated with a decreased MCOW. Seventy-six participants (42 Females, 24±5 years) completed a 5 stage, graded treadmill protocol with speeds increasing from 0.89-1.79 m/s (6-min walking stage followed by 4-minutes passive rest). Steady-state oxygen uptake (via indirect calorimetry) and stepping cadence (via manually counts) were determined. Gross and net MCOW, normalized to distance travelled (km) and step-cadence (1000 steps) were calculated for each stage. 39 participants (23 females) wore an activPAL on the thigh for 6.9±0.4 days. Normalized to distance, females had greater gross MCOW (J/kg/km) at all speeds (p<0.014). Normalized to stepping frequency, females exhibited greater gross and net MCOW at 1.12 and 1.79 m/s (J/kg/1000steps; p<0.01) but not at any other speeds (p<0.075). Stature was negatively associated with free-living cadence (r=-0.347, p=0.030). Females expend more energy/kilometer traveled than males, but normalizing to stepping cadence attenuated these differences. Such observations provide an explanation for prior work documenting higher MCOW among females and highlights the importance of stepping cadence when assessing the MCOW.