Energy cost of running uphill as compared to running on the level with impeding horizontal forces

We have previously shown that accelerated running on flat terrain is biomechanically equivalent to running uphill at a constant speed. This hypothesis was further investigated comparing the energy cost of running at a constant speed either uphill, or on flat terrain against an equivalent horizontal impeding force, mimicking acceleration.

Steady-state O₂ consumption and the corresponding energy cost (per unit body mass and distance) were determined on 12 male subjects during treadmill running at speeds between 2.11 and 2.89 m/s: (i) on the level, (ii) uphill at 10 or 20% incline ( $$ ), or (iii) on the level against a horizontal traction force of 10 or 20% of the subject's body weight ( $$ ). This allowed us to estimate the net efficiency ( $$ ) of running against horizontal or vertical forces, as given by the ratio between the additional mechanical work output under $$ , or the corresponding $$ condition, and the difference between the appropriate energy cost above that for running at constant speed on flat terrain.

The $$ values when running uphill ( $$ ) amount to 0.35-0.40, whereas those for running against an equivalent impeding force ( $$ ) are about 10% greater (0.45-0.50), a fact that may be due to a greater recovery of elastic energy in the $$ as compared to the $$ condition.

Making allowance for these small differences, these data support the view of considering accelerated running on flat terrain biomechanically equivalent to running at a constant speed, up an equivalent slope.