Bijan Najafi, at this year’s APMA meeting in Seattle presented some very compelling data that I think should cause us to think again about how we think 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 CLEAR 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 don’t 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. Perhaps also, these “pulses” are also better defined by the numbers of starts and stops– with the resultant increases in shear stress.
Perhaps that’s where damage occurs– on take off and landing (beginning and ending a series of steps). This might ultimately be considered conceptually similar to when most airline accidents occur– on take off and landing–rather than in midflight.
Let’s contemplate this as more data becomes available. We might be quantifying “gait initiation events” in future studies as a surrogate marker for danger.