What is the difference between walking and running? July 07 2015, 0 Comments
Locomotion when running is very different from when walking - for a start, when running we are airborne for about two thirds of the time, which is certainly not the case in walking. We have previously discussed running style, and a belief that a front-foot or mid-foot strike is healthier than a heel strike, but what changes when we launch from a walk into a run?
Harvard's Bramble and Lieberman discuss this in depth in a review written for Nature in 2004 (our illustration is from this). They examine the mechanical processes of walking and running, and then discuss how we have evolved into the formidable long-distance runners that we are now.
When walking, our weight never really leaves the ground, and at any time the maximum weight supported is equal to the body weight of the walker. With each stride, the foot reaches forward to land in a heel-strike (HS). Weight is transferred over the foot in mid-stride (MS) and then on to the other foot as it heel-strikes in its turn. Finally, weight is transferred off the rear foot with a 'toe-off' (TO) to move into the next stride. The head is at its highest point in mid-stride, where the leg is at its fullest vertical extension.
Contrast this with running, in which we are airborne at the time of contact, and the impact is about two-and-a-half times our bodyweight. The foot, ankle and knee are slightly flexed to absorb the impact and the centre of gravity pivots over the top of the foot into mid-stride. Much of the energy absorbed from impact is stored in the elastic Achilles tendon at the back of the leg, and those of the foot, and this is used to spring the toe-off into the next stride. Weight is never distributed between the two feet at the same time, and the head is at its highest point in the middle of the airborne stage.
Storing energy in our elastic lower-leg and foot tendons is an evolutionary trick for economical running. It ties in with other design features such as small feet (compared to other anthropoids), the concentration of muscle in the upper leg and our extra-ordinarily long legs and stride (longer than a horse...) for our body weight. Our barefoot running style has a pedigree of two million years development in the laboratory of evolution.