After learning to walk, walking becomes part of the natural gait, and running is an extension of walking. Running requires the coordinated movement of multiple groups of muscles, each delivering muscle contraction in aid of preparing the body for the next step of running as well as maintaining gait stability. But, what are the mechanics underpinning the performance of the human body under impact conditions? And what are the guiding principles underlying the efficient transfer of energy to the ground and the reduction of serious foot and knee injuries?
The answer: a running shoe that provides optimal and conformal fit to the foot where the upper mesh of the shoe hugs the upper feet surface in a tight but comfortable fit. But, what are the underlying mechanisms of this observation?
My personal experience in selecting running shoes and running reveals that when a foot sits almost exactly onto the insole and where an upper mesh hugs the upper surface of the foot in a tight fit, I usually have greater confidence in running. Why? Fast running and achieving greater propulsion requires the efficient transfer of energy from the feet to the ground which is closely tied to the next stage of running: liftoff. Both initial impact on the ground and subsequent liftoff from the forefoot can be viewed as a synchronized motion executed by the multiple small bones and tendons in the foot. In achieving efficient energy transfer to the ground necessary for subsequent forefoot liftoff that propels the body forward, the foot should not move or slide in the running shoe. Additionally, a foot that fits optimally into the running shoe enables the delivery of the downward stride onto the ground, with transfer of energy, on impact, that pass through the outsole thread. This energy transfer provides the reaction force from the ground that push the feet to move forward. Subsequent depression of the foam captures part of the energy that, when released upon liftoff, provides the lift for propelling the runner forward.
Besides improving performance and enabling a more joyful ride, having a tight fit in the running shoe also reduces the probability of injuries, given that foot movement in shoe is one of the main causes of improper foot landing that results in high impact stress on the knee and ankle. Having an optimal fit in the shoe meant two things: a shoe size that matches the dimensions of the foot as well as an upper mesh that fit closely onto the upper foot surface.
Altogether, running in a shoe with an optimal fit to the feet reduces feet movement in the shoe during impact, which directly translates into efficient energy transfer to the ground, and a natural gait that allows subsequent propulsion through forefoot liftoff. But, how does this work at the level of individual elements of the shoe? Specifically, how does the midsole interacts with the outsole to sustain the impact stress of a foot landing on concrete during fast running? The answer lies in the key enabler of a well fit between feet and shoe at the insole and upper mesh level. In experiential terms, the bottom of the feet must sit comfortably on the insole, which ideally should have contours matching those of the feet. At the mesh level, the stretchable breathable mesh provides another lock on feet movement in the shoe. Reducing feet movement (or sliding) in the shoe is critical to reducing injuries associated with running as well as providing the platform for transfer of as much energy as possible from the foot to the outsole through the compressive midsole foam layer. Thus, running fast and with confidence, with the later arising from knowledge of less impact stress on the ankle and knee, requires a good fit between the feet and shoe in the insole and at the upper mesh.
Category: sport science, materials, sport medicine,
Tags: upper mesh, insole, optimal fit, impact stress, knee, ankle, efficient energy transfer, forefoot liftoff, heel strike,
Acknowledgement: Ng Wenfa thank Seah Kwi Shan for co-authoring this blog post.