Person holding painful ankle on wooden floor

Kinesiology THURSDAY – Bicep Femoris v. Peroneus Longus (Tug-o-War Series)

Diagram showing biceps femoris and fibularis longus muscles.

The tug-o-war between bicep femoris (BF) and peroneus (fibularis) longus (PL) lies at the root of chronic lateral ankle sprains. Due to their common attachment at the fibular head, the BF exerts a superior/posterior force on the fibula, while the PL exerts an inferior force.

Studies have shown one of the risk factors of lateral ankle sprain is a previous ankle sprain. Subjects are 40% more likely to have chronic ankle instability in the year after an inversion ankle sprain. Let’s take a look at how the BF v. PL tug-o-war may be contributing.

  1. PL is an ankle evertor, therefore it is responsible for decelerating ankle inversion.
  2. PL weakness has been associated with lateral ankle sprains.
  3. BF is a knee flexor, but it also is responsible for decelerating lower leg internal rotation when the foot hits the ground. When the lower leg internally rotates, the foot pronates, allowing for shock absorption.
  4. If BF is tight, the foot will NOT pronate, causing over supination during stance phase.
  5. Hamstring tightness has been associated with chronic lateral ankle instability. Subjects in this study demonstrated decreased anterior reach with the leg on the side of tight hamstrings. This test is associated with decreased ankle dorsiflexion.
  6. Two motions that are lacking in individuals with chronic ankle instability: dorsiflexion and eversion
  7. With rapid ankle inversion, the distal PL bowstrings, pushing the distal fibula anteriorly and superiorly, causing superior/posterior migration of the proximal fibula. This makes PL long and weak and BF short and tight.
Anatomical diagram of the foot's peroneal tendons.

Here’s a simple fix. (If you aren’t a clinician but keep spraining your ankle, this is the part you want to pay attention to).

Man performing a standing twist stretch exercise.
  1. Stretch the BF with the revolving triangle pose. Make sure to keep your foot flat on the ground when you do this stretch. People with lateral ankle instability will tend to roll to the outside of the foot. Keeping your foot flat will maximize the stretch to the BF(hamstring). Here’s some other ideas to Wipe Out Lateral Ankle Sprains.
  2. Correct a posteriorly displaced fibular head with this MET. If the fibula is displaced posteriorly and superiorly, the BF will be short and tight and the PL will be long and weak.

Why does this matter?

Chronic lateral ankle sprains are often due to subluxation of the fibula in a posterior/superior direction. This creates a tight bicep femoris and weakness in the peroneus longus, the primarily muscle designed to decelerate ankle inversion. The fix doesn’t lie in doing resisted ankle eversion exercises, but rather in addressing this tug-o-war. So consider this relationship.

Because nobody has time to be in pain.

Until next time…

Kind Regards,
MoveWell Academy
[email protected]

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