We have all seen the arguments before: "Don't use foot orthotics as the weaken the arch muscles"; we have seen the same claims on many websites and forums. I love arguing with these people, and ask them what evidence to they have?: How do they know that this happens? They suggest that strengthening foot muscles can replace foot orthoses ... how do they know that?; etc. What I don't let on, is that I know what the evidence does say.
Lets look at some theoretical arguments first:
1. Basic functional anatomy: Look at any muscle chart and see when the intrinsic muscles of the foot fire...they don't fire until late in the stance phase just as the heel starts to come of the ground. How can strengthening those intrinsic muscles make any difference - if the foot pronates excessively or if the arch collapses, strengthening those muscles will make no difference as they do not even contract in time to prevent the arch collapsing and foot pronating.
2. Do you remember the diameter of those muscles from anatomy dissection? How can any muscle that small resist the kind of forces generated in gait anyway? (they can't!)
3. The intrinsic muscles do not even cross the subtalar joint, so how can they even stop a foot from pronating?
4. Why is it that those with intrinsic muscle atrophy actually develop a higher arched cavus foot (eg the 'intrinsic minus' foot seen in diabetes).Interesting how the 'believers' ignore this one!
Slam dunk? I have never seen anyone who argues for the 'muscles' even attempt to address these issues.
Now back to the evidence:
1. Mayer et al actually showed an increase in calf muscle strength with custom foot orthotic use.
2. We have data (not published yet) that showed an increase in toe plantarflexion strength (but it was not quite statistically significant) after 4 weeks of foot orthotic use.
Certainly no sign of any muscle weakness occurring from the two studies that have looked at. Why do so many continue to promote this concept when the theoretical arguments and the evidence does not support it?
I also blogged about: Do running shoes weaken muscles?