Development and validation of a steep incline and decline metabolic cost equation for steady-state walking

The purpose of this study was to develop and validate a data-supported prediction equation (Lankford equation) for walking metabolic cost ([Formula: see text]), and to compare this equation to the ACSM, Pandolf, Minetti, and LCDA equations. The current study also investigated how kinematics of incline walking relates to mechanical efficiency and metabolic cost.

Subjects consisted of 145 recreationally fit individuals. Walking speeds were between 1 AND 3 mph with grades ranging from - 18 to 40%. The Lankford equation was then compared to four other reference equations using adjusted R-squared (R²) and Root Mean Square Error (RMSE) as primary metrics to determine correlation with measured C_W. Kinematics data collected from reflective markers placed on bony landmarks were compared to C_W, incline, and metabolic efficiency to determine the interrelationship between these variables.

The Lankford equation for estimating [Formula: see text] was validated with an adjusted R² = 0.89 and a RMSE of 5.92 Kj min^-1, shown to have the highest accuracy among all equations tested. A 0.21 efficiency plateau was observed above 15% incline, and hip, knee, HAT, thigh, and shank angles at foot touch down were found to be highly correlated with [Formula: see text] (r > 0.980).

The Lankford equation is a validated and highly accurate prediction equation for steady-state walking across a wide range of inclines and speeds and is applicable to the general public. Altered leg swing observed above 15% incline was found to account for the mechanical efficiency plateau and the rectilinear increase in [Formula: see text] with increasing incline.