I think I know why you are confused. I fear you are working from a flawed premise. Tissue stress theory covers saggital plane theory as well.
For eg. What is the role of the plantar apeurneurosis? Partly to resupinate the foot at heel raise as per the windlass effect right? So you can reduce the amount of strain on the plantar fascia by reducing the amount of force needed to resupinate the foot. One way to do that is to plantarflex the first met. To plantarflex the 1st met you can do one of two things. 1. Raise the base of the met (arch support) or 2, drop the head of the 1st met (kinetic wedge / reverse mortons extension).
They are both tissue stress interventions. Both increase hallux plantarflexion (which, of course is in the sag plane). Therefore both are tissue stress interventions AND sagittal plane interventions.
For some reason however, 1 is seen as a "frontal plane" modification and the other a "sagittal plane" modification. In fact they are both triplanar modifications, both based on tissue stress theory and both work by adjusting the function of the windlass, which operates almost entirely in the sagittal plane.
Specialist in Biomechanical Therapies
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