In previous articles I’ve discussed several of the common strength and mobility problems that cause of overpronation. Some of the major factors covered up to this point have include weak foot musculature, limited dorsiflexion range of motion, and anterior pelvic tilting. This post addresses the role of inversion and eversion strength in controlling pronation.
Ankle inversion and eversion are motions that come primarily from the subtalar joint–the joint between the calcaneus (heel bone) and the talus bone. Inversion can be seen when you point the sole of your foot towards the opposite foot without moving the rest of your leg. Eversion is the opposite motion as inversion.
When the foot is in contact with the ground, too much eversion contributes to overpronation.
In order to prevent this excessive pronation the anterior and posterior tibialis muscles have to be strong enough resist the eversion forces to pull the foot into inversion. Weakness and degeneration of the posterior tibialis is known to be one of the main causes of flat foot deformity in older adults.
One study found that strengthening both inversion and eversion was able to reduce the amount of pronation in runners. The study split 22 runners with excessive pronation into two groups. The experimental group performed isokinetic inversion and eversion exercises 3 times a week for 8 weeks. The control group did exercises “commonly used in ankle rehabilitation”.
The group performing the inversion and eversion strengthening exercises showed a marked decrease in their pronation measurements.
Even though the size of the study was small and the researchers used isokinetic exercises (expensive variable resistance machine required) the results should be encouraging to anyone looking to correct their pronation problems. The easiest way to do inversion and eversion strengthening at home is to use exercise bands for resistance.
I’ll usually aim for 3 sets of 20 to 30 reps. Starting with the band in a more stretched position increases the resistance no matter what strength band you are using.
The other variable that can easily be modified is the positioning of the exercise. To get the most benefit these should be done both with the leg extended (as in the pictures) and sitting on a chair with the knee bent. Bending the knee alters the way the muscles are recruited.
A full description of the resistance band exercises can be found here.
Why are these exercises effective?
I can understand why strengthening inversion would help with pronation but I wasn’t sure why working eversion would have any benefit. I came across this study that was published in the Journal of Foot and Ankle Research. The study found that people with flat feet showed greater EMG muscle activity of the invertor muscles (tibialis posterior and anterior) and decreased activity of the evertor muscles (peroneals).
This is only one study but it makes sense that for someone whose arch is collapsing that the invertor muscles are going to be trying really hard to pull the arch up and the muscles that evert the foot are going to stay relaxed in order to not put any more pressure on the foot to pronate.
This also is consistent with other research showing adults who acquire a flat foot deformity due to posterior tibialis dysfunction actually had slightly flat feet to begin with. The abnormal stresses caused by that position likely weakened the muscle over time.
So the reason to strengthen the invertors is pretty clear. But why make the evertor muscles stronger? Two theories that I can come up with:
- First the two muscles groups have to work together for walking and running, the invertors on the inside of the ankle and the evertors on the outside. It’s possible that exercising one group will indirectly improve the function of the other.
- Secondly, with an unstable ankle or one that has been sprained may go into a pronated position as a way to stabilize the ankle and prevent it from rolling inward. The initial instability could likely be weakness of the evertors. Therefore, strengthening them increases overall ankle stability and removes that incentive to pronate.
- Lastly, the peroneal longus (an evertor muscle) crosses the underside of the foot and pulls the inside of the forefoot down. This action helps stabilize the arch.
Confused yet? Biomechanics create a lot of confusion and I’m not sure anyone has all the answers. Bottom line: strengthen everything and then use that strength to keep a stable arch.
Exercise equipment vs. new car
Finally, for anyone curious this is what isokinetic inversion and eversion strengthening looks like: (Video). The isokinetic machines are usually found in rehab clinics. They’re nice because they provide variable resistance and are relatively safer than free weights.
The disadvantages, other than the cost of the equipment, are the fixed range of motion set by the machine and the isolation of the joint being exercises, meaning stabilizing muscles outside of that joint are not getting strengthened at the same time. Unless you have access to one at the gym, it’s probably not worth spending $50, 000 just to do some ankle strengthening. Exercise bands can be found at most sporting good stores and come in handy for several other ankle strengthening exercises which I’ll cover in the near future.
Has anyone used ankle strengthening exercises to help their running form or pronation issues? Do you think the exercises were effective?