Does Stress During Walking Occur During Foot ‘Takeoff’ And ‘Landing’ Rather Than ‘Midflight’?

At this year's American Podiatric Medical Association (APMA) meeting in Seattle, Bijan Najafi, PhD, presented some very compelling data that may force us to rethink what we know about repetitive stress in walking.

For many years, we have posited that plantar pressure x cycles of stress = ulcer. More recently, this has been refined to theoretically include shear stress along with normal stress. This begs the question: where does damage occur?

The interesting preliminary data from Dr. Najafi's lab at the Center for Lower Extremity Ambulatory Research (CLEAR) at the William M. Scholl College of Podiatric Medicine at the Rosalind Franklin University of Medicine and Science in Chicago has allowed us to peer into different types of activity. The sensors being used now can give clarity about walking, running, standing, sitting and jumping.

What we can see for the first time is that many patients have starts and stops during their day that do not typically show up in a standard step counting/activity monitoring measurement.

We have shown some years ago that "pulses" of activity may predict the onset of neuropathic ulcers in people with diabetes. Additionally, perhaps these "pulses" are also better defined by the numbers of starts and stops — with the resultant increases in shear stress.

Perhaps that is where the damage occurs — on takeoff and landing (beginning and ending a series of steps). This might ultimately be considered conceptually similar to when most airline accidents occur: on takeoff and landing, rather than in midflight.

Let us contemplate this as more data becomes available. We might be quantifying “gait initiation events” in future studies as a surrogate marker for danger.

This blog has been adapted with permission. It originally appeared at

crstuartsays: August 2, 2010 at 7:17 am

I have seen quite a few patients, both diabetic and non-diabetic, in my office with a callus under their plantar medial hallux. Several of these patients have reached the point of ulceration in this area. My understanding of the biomechanics is that the location of this ulcer is secondary to hyperpronation and the stress of toe off ("Take off").

I have tried to use orthotics, either prefabricated or custom, and I build up the medial arch hoping that this will decrease the degree of shear force under the plantar medial hallux by decreasing the abnormal pronation at the STJ. Does anyone have any other strategies in diminishing the degree of shear stress under the plantar medial hallux?

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