Actually…
After doing a little research I find that there is some truth to Goose’s discussion of gravity and sprinting. While there is no horizontal component to gravity, there is interaction between gravity, kinetic energy, and something called the pendulum effect. The article below is about walking, but I would it transfers to running as well.
The role of gravity in human walking: pendular energy exchange, external work and optimal speed
G A Cavagna, P A Willems* and N C Heglund*
+Author Affiliations
Istituto di Fisiologia Umana, Università degli Studi di Milano 20133 Milan, Italy
*Unité de Réadaptation, Université catholique de Louvain 1348 Louvain-la-Neuve, Belgium
Corresponding author G. A. Cavagna: Istituto di Fisiologia Umana, Via Mangiagalli 32, 20133 Milano, Italy. Email: giovanni.cavagna@unimi.it
Abstract
1.During walking on Earth, at 1.0 g of gravity, the work done by the muscles to maintain the motion of the centre of mass of the body (Wext) is reduced by a pendulum-like exchange between gravitational potential energy and kinetic energy. The weight-specific Wext per unit distance attains a minimum of 0.3 J kg−1 m−1 at about 4.5 km h−1 in adults.
2.The effect of a gravity change has been studied during walking on a force platform fixed to the floor of an aircraft undergoing flight profiles which resulted in a simulated gravity of 0.4 and 1.5 times that on Earth.
3.At 0.4 g, such as on Mars, the minimum Wext was 0.15 J kg−1 m−1, half that on Earth and occurred at a slower speed, about 2.5 km h−1. The range of walking speeds is about half that on Earth.
4.At 1.5 g, the lowest value of Wext was 0.60 J kg−1 m−1, twice that on Earth; it was nearly constant up to about 4.3 km h−1 and then increased with speed. The range of walking speeds is probably greater than that on Earth.
5.A model is presented in which the speed for an optimum exchange between potential and kinetic energy, the ‘optimal speed’, is predicted by the balance between the forward deceleration due to the lift of the body against gravity and the forward deceleration due to the impact against the ground.
6.In conclusion, over the range studied, gravity increases the work required to walk, but it also increases the range of walking speeds.