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Born to Run? Exploring Dr. Irene Davis’s work on gait and running

During 2013-2015 I had the good fortune of volunteering at the Biomedical Imaging Lab at UCSF. The post doc researchers there were working on several cool movement science projects. The project that I was able to volunteer on was a longitudinal study that looked at cartilage volumes within the knees of folks who had been diagnosed with osteoarthritis. People living with knee osteoarthritis often assume a toe out gait. Because how we move changes forces at the joints, the theory was that as we taught the subjects to walk with a more mechanically sound posture (in our instance, with their toes forward).

Walking with our toes forward is a crucial aspect of healthy gait, as it allows for the extension at the big toe, the activation of our windlass mechanism within our plantar fascia and maximal efficiency at the calf.

It also protects our knee joints and hip joints from excessive motion in the transverse (rotational) planes. Recall that the knee is meant to function truly as a hinge joint.

Dr. Perry was a foundational pillar for how we understand the biomechanics of walking, and the incredible biomechanist Irene Davis PhD, PT helped us move beyond walking to understand the forces that we expose our bodies to as we run.

Unlike walking, which is a series of double leg stance and single leg stance, running requires alternating periods of flight and single leg stance.

When we add the element of flight, we greatly increase the forces that the body is subjected to. This is largely because of Newton’s law- Force= mass x acceleration. When we run, we greatly increase our acceleration, thereby greatly increasing the forces we must effectively control.

The force we want to specifically explore, is the ground reaction forces. Ground reaction forces (or GRF in movement nerd speak) occur whenever we move over a surface. We push down onto that surface (the earth, a force plate, a diving board) and that surface creates a force back up through our bodies. The GRF increases greatly when we increase either our mass or our acceleration.

Through her years of research into running mechanics, Dr. Davis found that that predisposition for injury is not so much about whether or not we run (or how much) but truly how we run.

There are two general ways runners navigate increased ground reaction forces: they dampen the force that comes up through the lower limb by using the calf (gastroc and soleus) muscle and intrinsic foot muscles, or they don’t reduce the forces and the ground reaction force goes straight into the lower limb (specifically affecting the knee joint and tibia).

Interestingly, these two strategies are aligned with two very different running styles- a heel strike and a mid/ forefoot landing.

Dr. Davis found that folks who use a heel strike when landing on their single leg after a flight phase, cannot access their posterior muscles to effectively reduce the GRF their body is subjected to, and therefore they have a greater tendency towards orthopedic conditions related to too much force: everything from shin splints, to stress fractures of the lower leg to fatigue of joint cartilage in the lower limb (which is associated with early osteoarthritis).

Contrary to the heel strike running style, is the fore/mid foot running pattern.

In this running style, athletes land on their fore-mid foot after a flight phase. The position of the foot in this gait style allows the mover to use the sole of their foot and their posterior chain to dampen down the GRF. Much greater strength is required at the foot as well as gastroc/soleus- and much less force is transmitted up through the passive structures of the lower limb.

Dr. Davis went on to note that shoe wear greatly influences our running mechanics. When we run in shoes with a large, built up cushioned sole, we tend to favor heel striking. Dr. Davis herself runs with barefoot shoes, to encourage the mid- fore foot striking.

If you run yourself and would like to try the fore-mid foot method of running, try out a pair of barefoot running shoes. Think, as you run, of landing softly. I try to run this way, and my calf strength continues to be my limiting factor.

And the next time someone gives you advice about running, I would make sure they are watching you run with an eye for whether you are heel or fore foot striking. All the better if they also ask you about your shoe wear, have force plates, motion capture cameras - and a PhD in biomechanics wouldn’t hurt!

Happy moving!


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