The energy cost of walking or running on sand

Oxygen uptake ( {Mathematical expression}O2) at steady state, heart rate and perceived exertion were determined on nine subjects (six men and three women) while walking (3-7 km · h-1) or running (7-14 km · h-1) on sand or on a firm surface. The women performed the walking tests only. The energy cost of locomotion per unit of distance (C) was then calculated from the ratio of {Mathematical expression}O2 to speed and expressed in J · kg-1 · m-1 assuming an energy equivalent of 20.9 J · ml O2-1. At the highest speeds C was adjusted for the measured lactate contribution (which ranged from approximately 2% to approximately 11% of the total). It was found that, when walking on sand, C increased linearly with speed from 3.1 J · kg-1 · m-1 at 3 km · h-1 to 5.5 J · kg-1 · m-1 at 7 km · h-1, whereas on a firm surface C attained a minimum of 2.3 J · kg-1 · m-1 at 4.5 km · h-1 being greater at lower or higher speeds. On average, when walking at speeds greater than 3 km · h-1, C was about 1.8 times greater on sand than on compact terrain. When running on sand C was approximately independent of the speed, amounting to 5.3 J · kg-1 · m-1, i.e. about 1.2 times greater than on compact terrain. These findings could be attributed to a reduced recovery of potential and kinetic energy at each stride when walking on sand (approximately 45% to be compared to approximately 65% on a firm surface) and to a reduced recovery of elastic energy when running on sand. © 1992 Springer-Verlag.