MECHANICAL ENERGY DIFFERENCES BETWEEN WALKING AND RUNNING AT DIFFERENT VELOCITIES ON TREADMILL

Abstract

INTRODUCTION: Cavanagh (1990) described a variation from 170 to 1700 W in power output for the same movement (running at 3.6 m/s) calculated by six different authors. These differences occurred mainly due to different procedures for energy calculation and generated data that are not comparable. The purpose of this investigation was to describe, analyze, and compare the mechanical energy curves (total, internal and external energies) for six subjects while walking and running on treadmill, by using the same procedure for energy calculation. METHODS: Six male subjects were filmed with two video-cameras (Sony-50Hz) while walking at 1.5 m/s and running at 3.0 and 4.0 m/s on a treadmill. After a manual digitizing process, a 3D analysis was performed from the kinematics. The analysis was based on a 13 segment model. Positions of segmental centers of gravity, segmental weights, and moments of inertia were estimated on the basis of tables devised by Dempster (1955) as revised by Winter (1979). The components of mechanical energy were calculated at each instant of time, using the equations described by Zatsiorsky et al. (1987). RESULTS AND DISCUSSION: In relation to the differences between walking and running, the following observations were made: a) in walking the greatest contribution to the total change derived from the internal energy, while in running it derives from the external energy; b) the internal and external energy were in phase in walking, and in opposition in running. Comparing the variations in the two velocities of running, the following conclusions were drawn: a) the average value of the absolute total energy at 3.0 m/s was 1237.9 J and at 4.0 m/s 1544.2 J; b) there was a linear correlation (r = 0.84) between the change in velocity and the change in total energy; b) with the increase in velocity, the average increase in the total contribution of the change in internal energy was about 72% and of the external energy 36%; c) there was no change in the contribution of the potential energy to the change in external energy; d) the increase in the internal energy was chiefly dependent on the increase in the kinetic energy. CONCLUSION: Although the results related to the shape of the curves for mechanical energy for walking and running are already a matter of consensus in the field of biomechanics, it would appear that the numerical results are still open to broad discussion.