Craig, you alos refer back to a study you undertook regarding heel lift - was you defintion of 'weight coming off the heel' the point at which it started to unload i.e. past the point of maximum force, or when the heel was no longer wieghtbearing?
Used a heel mask and looked at two points. One was the point at which the heel started to unload. Another was when it was unloaded 90% of max load; then also used that info to derive a "slope of the unweighting" line ..
That's a function of midfoot rigidity and ankle plantar flexion moment.
That slope should also correlate with the velocity of center of pressure.
It would be interesting to look at the effect of rocker tip outersoles on the velocity of center of pressure.
With rocker tip soles it has been shown that heel contact is longer and forefoot pressures are lower.
So, midsole configuration could really affect the velocity of center of pressure.
The term "ride" of a running shoe reminded me of the 70's TV show American Bandstand.
On the show they would ask teenagers to rate newly released songs.
The teenagers would invariably say that it had a good beat and that you could dance to it.
Or, not.
I would much rather listen to people talk about biomechanics of the foot than to talk about music.
That slope should also respond to Ankle joint dorsiflexion ROM. The less Dfion at the Ankle the sooner the heel will off weight. The speed of the off weighting should correspond to midfoot/forefoot stiffness. Increased midfoot/forefoot stiffness with decreased AJ ROM means faster off weighting and vice versa.
As far as the distal shoe rocker, I think what matters is where the rocker actually starts. The more proximal it starts the less of a delay in heel off weighting there should be.
Thanks!
Bruce
An early heel off from an equinus is plantar flexion moment.
However, someone with normal range of motion of ankle could choose to contract their Gastroc soleus creating a plantar flexion moment that would shift the center of pressure forward.
So, it is possible to see this in the absence of an equinus.
So a bot like everything - the degree of calf flexibility, the relative midfoot stiffness, the individuals muscle tuning and day to day response, the actual midsole materials (and thus effect on tuning), stack height, location of rocker and any other proximal issues / step length etc. are all likely to influence the heel raise and Velocity of the CoP.
Craig, out of interest, how did you actually calculate the slope of unweighting, was it the degree of change over time?
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