„A chain is no stronger than its weakest link.“ (William James)
Effective and efficient energy transfer is nature’s first principle of design. It is evident in all biological systems and structures, as well as the behaviours they facilitate. For example, human walking is characterised by the rhythmic exchange of potential and kinetic energy, essentially producing a zero-sum kinetic chain, so minimising energy expenditure. The foot is the first and critical link in this chain. A new study in the prestigious journal Nature is the first to explain how the foot accomplishes this unique role.
Takahashi et al. (2017) used the motion of and forces produced by the feet of teenage participants during barefoot walking to calculate energy produced and absorbed by the toes, midfoot and rear foot independently. Results showed that energy absorbed by elastic and compliant structures was perfectly balanced out by energy actively produced, making the foot energy neutral.
The study concluded that this energy-neutral behaviour was likely a hallmark of a healthy foot and ankle system. This illustrates the importance of freely-functioning feet in coordinating the walking pattern, and how a compromised/weak first link can disrupt the entire kinetic chain.