09 Mar Walking is a heel-toe gait – part 1
„Nothing in biology makes sense except in light of evolution.”
Theodore Dobshansky (1973)
Humans are adapted bipedal walking and running specialists, with walking being the most used of these two gait patterns. Nature’s prime directive in adapting organisms is the minimisation of energy cost, as energy is the currency of life (Sparrow, 2000). Structural adaptations in humans from our tree-climbing ancestors can be easily tracked in the fossil records and show how natural selection shaped humans to walk with minimum energy expenditure (Rodman and McHenry, 1980). This evidence and the evolutionary drive to minimise energy cost seems to have been ignored by modern proponents of forefoot walking. This piece will dispel the myth that humans are evolved to walk on the forefoot.
The energy cost of walking is paid per step i.e. every time bodyweight is supported against gravity. Energy costs are incurred when support is more frequent, when muscles are required to counter/produce force at joints, and when support time is shortened (Heglund, Cavagna & Taylor, 1982). To minimise energy cost in walking, humans evolved long straight legs, and strong-short rounded heels protected by thick fat pads. Long legs give a long stride meaning weight is supported less often and for longer over any given distance, thus saving energy. An extended leg naturally contacts the ground with the heel first. The strength, shape and protection of the heel bone are the adaptations facilitating this. The short-rounded heel allows a smooth vaulting action of the body over the extended support leg from where it simply falls onto the next outstretched leg. This rhythmic rise and fall can be modelled as a simple inverted pendulum where the torso is the weight and the leg is the pendulum arm. This model describes with great accuracy what actually happens in walking humans (Srinivasen and Ruina, 2006).
In contrast, forefoot walking requires a shorter stride (costing energy) or an active downward flex of the foot at the ankle (costing energy) to avoid the heel contact that naturally happens with an extended stride. Force is required by the calf muscles to smoothly lower the heel as weight is transferred to the extended leg (costing energy). In every sense, forefoot walking is ‘unnatural’, making no sense in light of physics or evolutionary biology. The additional muscular effort and energy cost of a contrived forefoot-walking gait are unnecessary and misuse structures shaped by natural selection to minimise both.
Dr. Mick Wilkinson, PhD, MSc, BA (Hons)
Northumbria University, Newcastle, England
Senior Lecturer in Sport and Exercise Science & Department Ethics Lead
Heglund, N.C., Cavagna, G.A. and Taylor, C.R. (1982). Energetics and mechanics of terrestrial locomotion. Journal of Experimental Biology, 79, 41-56.
Rodman, P.S. and McHenry, H.M. (1980). Bioenergetics and the origin of hominid bipedalism. American Journal of Physiology and Anthropology, 52, 103-106.
Sparrow, W.A. (2000). Energetics of Human Activity. Chapaign, Illinois: Human Kinetics.
Srinivasen, M., and Ruina, A. (2006). Computer optimization of a minimal biped model discovers walking and running. Nature, 439, 72-75.