Airbus A300 during the pull-in of a parabola simulating hypo-gravity (photo NOVESPACE)

During walking, the center of mass of the body is subjected each step to gravitational potential energy changes, W_v, and to kinetic energy changes of forward motion, W_f. On Earth, at 1.0 g of gravity, the actual work done by the muscles to maintain the motion of the centre of mass, W_ext, is reduced below the sum of W_v + W_f by a pendulum-like transfer of potential energy into kinetic energy and vice-versa. On Earth, 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, and the walk-run transition occurs at about 8 km h^-1.

The effect of a gravity change on this mechanism 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 (23rd and 24th parabolic flight campaign of ESA).

At 0.4 g, such as on Mars, the minimum W_ext half that on Earth, and occurs at a lower speed  (about 2.5 km h^-1). The range of possible walking speeds is smaller than at 1.0 g, with the walk-run transition occurring at about 6 km h^-1.

At 1.5 g the lowest value of W_extis twice that on Earth, and is maintained nearly constant up to about 4.3 km h^-1, then it increases with speed. The maximum walking speed is likely to be larger than on Earth, probably attaining a value of about 10 km h^-1.

In conclusion, gravity increases the work required to walk, but it also increases the range of possible walking speeds.

During the 32th parabolic flight campaign of ESA, we studied the effect of hyper gravity  (1.3 g) on the mechanics of running. Results are presently analyzed.

This work is directed by Prof. G.A. Cavagna (Istituto di Fisiologia Umana, University di Milano, Italie).

CAVAGNA G.A., HEGLUND N.C. & WILLEMS P.A. (2005) Effect of an increase in gravity on the power output and the rebound of the body in human runnning. J. Exp. Biol. 208: 2333-2346

CAVAGNA G.A., WILLEMS P.A. & HEGLUND N.C. (2000) The effect of gravity on the mechanics of the walking gait. J. Physiol., London. 528: 657-668

CAVAGNA G.A., WILLEMS P.A. & HEGLUND N.C. (1998) Walking on Mars. Nature 393: 636

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