My queries are 2 fold:
1. Do you think the abscence of connective tissue, muscles and tendons
(by lack of their inhibiting affects) allows for this kind of
2. Although you applied a ground reaction type force, would the same affect
occur if the force were applied during amubulation?
Let me answer you in a round about way. I have been developing a new hypothesis for why Chiropractic works. I have been borrowing quite a bit from Gracovetsky's work on the spinal engine. He state that the spine ocillates in the gravitational field and that impulsed feed the spine during gait supply its potential energy. This implies that the lower extremities are "amplifiers" of impulses to the spine. Which, in turn, implies that the feet must efficiently transfer this impulse as well. I won't bore you with an explaination of segmental vs summary force transfer and the role of the neuromuscular component, suffice to say that If I can nail down pathomechanics, normal is not as big an issue.
So, the short version is that there is an increase in stability of these feet because they are fixed, at the same time instability because musculature is missing. BUT..... during the entire obsevation, the joint surfaces remained congruent. That is, nothing I did dislocated a joint, (subluxed, yes) suggesting all positions were in the realm of posibility for a living individual. In fact, I did not even stress this foot enough to produce a Charot type positioning.
As for the ground reaction force. I did exactly as you suggest. It occured to me that dorsiflexing the foot passively could not possibly produce the same effect as a true ground reaction. The motion used was similar to gait at initial FF loading.
One last note on inhibiting effects of musculature..... I haven't published this yet, but I have seen in the lab myotonia of muscles affecting joints that are dysfunctional. Initial EMG studies bear this out as well. The implication is interesting. If I have a mild joint injury and develope secondary myotonia, does this predispose me for further injury and increased myotonia? How much myotonia is enough to be of issue? Do I merely have to void the normal muscular balance, or develope obvious weakness? I have some suspicions, but I would like to hear what others have to say.