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Step frequency and energy expenditure are greater in backward running than in forward running. The differences in the motion of the centre of mass of the body associated with these findings are not known. These differences were measured here on nine trained subjects during backward and forward running steps on a force platform at 3-17 km h-1. In contrast to previous reports, we found that the maximal upward acceleration of the centre of mass and the aerial phase, averaged over the whole speed range, are greater in backward running than in forward running (15.7 versus 13.2 m s-2, P=1.9×10-6 and 0.098 versus 0.072 s, P=2.4×10-5, respectively). Opposite to forward running, the impulse on the ground is directed more vertically during the push at the end of stance than during the brake at the beginning of stance. The higher step frequency in backward running is explained by a greater mass-specific vertical stiffness of the bouncing system (499 versus 352 s-2, P=2.3×10-11) resulting in a shorter duration of the lower part of the vertical oscillation of the centre of mass when the force is greater than body weight, with a similar duration of the upper part when the force is lower than body weight. As in a catapult, muscle-tendon units are stretched more slowly during the brake at the beginning of stance and shorten more rapidly during the push at the end of stance. We suggest that the catapult-like mechanism of backward running, although requiring greater energy expenditure and not providing a smoother ride, may allow a safer stretch-shorten cycle of muscle-tendon units. [ABSTRACT FROM AUTHOR]

Elephants are the biggest living terrestrial animal, weighing up to five tons and measuring up to three metres at the withers. These exceptional dimensions provide certain advantages (e.g. the mass-specific energetic cost of locomotion is decreased) but also disadvantages (e.g. forces are proportional to body volume while supportive tissue strength depends on their cross-sectional area, which makes elephants relatively more fragile than smaller animals). In order to understand better how body size affects gait mechanics the movement of the centre of mass (COM) of 34 Asian elephants (Elephas maximus) was studied over their entire speed range of 0.4-5.0ms-1 with force platforms. The mass-specific mechanical work required to maintain the movements of the COM per unit distance is ∼0.2Jkg-1 m1 (about 1/3 of the average of other animals ranging in size from a 35g kangaroo rat to a 70kg human). At low speeds this work is reduced by a pendulum-like exchange between the kinetic and potential energies of the COM, with a maximum energy exchange of ∼60% at 1.4ms-1. At high speeds, elephants use a bouncing mechanism with little exchange between kinetic and potential energies of the COM, although without an aerial phase. Elephants increase speed while reducing the vertical oscillation of the COM from about 3cm to 1 cm. [ABSTRACT FROM AUTHOR]

The article focuses on the analysis of the elephant's movements to determine whether they are walking or running. According to John Hutchinson from the Royal Veterinary College in Great Britain, fast-moving elephants seems like running at a first glance. It mentions that a team consisting of Norman Heglund, Joakim Genin and Richard Lair found out that the movements of the elephant's center of mass look like walking at low speeds but look like running as they move faster.