Understanding The Impact of Muscle Weakness
- Volume 15 - Issue 4 - April 2002
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Muscle strength testing is not always part of a standard podiatric biomechanical evaluation. Unfortunately, muscular weakness can often influence function and, if undetected, can lead to chronic pain in the joints which the weakened muscles support. There are several reasons for muscular weakness, but the most common cause is chronic inhibition signaling from the CNS. Since motor signals to muscles normally cycle between facilitation (excitation) and inhibition, an alteration in this signaling can often cause chronic inhibition and subsequent pain.
With this in mind, our expert panelists offer their opinions on how you can use this effect to manage a variety of common podiatric conditions.
Q: What is the effect of peroneal inhibition on normal foot function?
A: Hallux limitus/rigidus, hallux valgus and sesamoiditis can all be related to suppressed function of the peroneal muscles, according to Howard Dananberg, DPM. Often, this can occur following a subtle inversion ankle sprain-type injury and lead to pain in and around the first MTPJ.
The peroneals have both an eccentric and concentric function during gait, notes Trevor Prior, FCPod(S). In latter stance, as the heel starts to lift from the ground, first MTPJ dorsiflexion and ankle plantarflexion should occur. This motion initiates the windlass mechanism as the fascia begins to tighten. In turn, this will cause plantarflexion of the first metatarsal, which is stabilized against the ground by peroneus longus activity, according to Mr. Prior. As the tendon of peroneus longus pivots around the cuboid, it will cause some rotation and ultimately close packing of the calcaneocuboid joint as described by Bojsen-Moller.
“Inhibition will affect the ability of peroneus longus to stabilize the first ray and predispose to instability,” notes Mr. Prior. “It may be difficult to determine whether first MTPJ dysfunction (due to functional hallux limitus, rearfoot pronation, etc.) prevents normal peroneal activity or vice versa. The net result is dysfunction.”