Foot Biomechanics

Every year, millions of people are victims of horrible accidents; whether it’s work-related injuries, automobile accidents, or incidents at home. It’s true that a lot of these people die because of their severe injuries; however, a considerable number survives!

​Unfortunately, in many cases, the survivors lose a part of their bodies or their functionality. Lower limb amputation is one common surgery performed to save the victim’s life, especially after automobile accidents.
After the limp is amputated, patients are often provided with a prosthesis and are advised to go through physical rehabilitation to at least gain back some function.

The two main factors that predict how will the patient progress in his/her therapy and what kind of results to expect are:
1-The patient’s mental resiliency and willpower.
2-The quality of the prosthesis provided.
The first factor is hard to quantify and can be improved by psychotherapy sessions to help the healing process. The second factor; however, is where we come in!

The science of studying the biomechanics of the foot has helped develop more advanced prosthesis and wearable assistive devices with a significantly better functionality; this is why it’s very important to keep digging to reach a comprehensive understanding of the foot’s biomechanics and energetic behaviour during running.

So, let’s start by asking ourselves a couple of questions:
How does the human foot’s energy status fluctuate during running? What role do the biological components (e.g. muscles, ligaments, tendons, plantar fascia) of the foot play during walking and/or running? How can we reach a better understanding of the biomechanics and the energetic behaviour of the foot?
These questions may sound daunting and even futile at first, but that’s far away from the truth! You see, for each question answered, we are one step closer to creating better versions of artificial prosthesis and wearable assistive devices.     

​To answer these questions, Luke Kelly, a podiatrist at the University of Queensland and his colleagues conducted experiments on 14 participants. The results were published in many reputable magazines such as Nature.
Luke and his colleagues brought 14 healthy males and asked them to run on a force-instrumented treadmill, which is a treadmill with fancy equipment that measures force, speed, angle, and time of contact between the foot and the treadmill.
Luke divided the experiments into three phases; at each phase, the treadmill’s configurations were set to a different speed starting at a slow speed and then accelerating in the next phase.
Using the sensitive sensors on the AMTI treadmill, we can measure all different kinds of parameters of the running participants at different speeds.

​The goal of this study was to determine whether the foot acts as a spring that stores energy then returns it, or as a damper that dissipates energy, and the overall contribution of all active and passive tissues that work together to produce the necessary energy during running.
For example, the plantar fascia which is a structure composed of soft tissue located at the bottom of the foot acts as a spring during running; it stores the mechanical energy then releases it.
On the other hand, the fat pads located at the heel and the front of the foot act as a damper that stores energy and dissipates some of it.

The energetic behaviour of the foot was often thought of as having spring-like qualities. In order words, muscles, ligaments, and tendons were considered as spring-like structures that absorb mechanical energy during the early and mid-stance phases, just to return that energy in the late stance phase which contributes to 8-17% of the energy needed for each step. This fitted the concept of energy conservation that was proposed and that was that.
In this study; however, energy dissipation from different tissues such as muscles and fat pads was noted, with approximately 20-50% of the energy absorbed by the fat pads getting dissipated.
The amount of energy being dissipated is proportionally increased with velocity. This behaviour resembles the model of a viscoelastic damper rather than the spring model proposed earlier.

This might seem counter-intuitive at first. Why would such a considerable amount of mechanical energy be dissipated? This means that the exact amount has to be generated by muscular contractions elsewhere in the body. Why waste energy?
The study suggests that the energy dissipation may help with slowing centre of pressure (COP) progression; thus, prolonging contact-time between the foot and the floor which will maximise the time for propulsive impulse (energy to take a step) generation. Eventually, this will help significantly with energy savings that otherwise would have been generated by other muscular groups.
The results of this study have the potential to change how we view and design prosthesis and wearable assertive devices. The new models can be much more energy-efficient and will improve the interaction of these devices with humans.

​Conclusion
Even though the results of this study are quite intriguing and open the door for multiple innovative designs of prosthesis; we need to do more research and investigation to get a clearer view on how the overall energy profile and biomechanics of the foot function and the interaction between different structure on an energetic level.

Source:
Kelly, L., Cresswell, A. and Farris, D. (2018). The energetic behaviour of the human foot across a range of running speeds. Scientific Reports, [online] 8(1). Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6043578/pdf/41598_2018_Article_28946.pdf [Accessed 7 Oct. 2019].

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