Eugene Movement Center

Functional Mechanics of the Peroneus Longus. Ankle rehab, prehab and activating the spring system of the foot.

Standard kinesiology says that the peroneus longus plantar flexes and everts the foot. This is functionally not what is does, however. It's primary function is to slow down the force of gravity as the foot comes crashing into the ground, absorb that force, and hold the foot on the ground as the knee and hip extend.

Functionally, it eccentrically loads as the forefoot enters the ground and decelerates dorsiflexion of the first ray (joint of the first metatarsal and middle cuneiform) and holds it on the ground for push-off of the big toe. Also, it decelerates dorsiflexion of the ankle, midtarsal joint inversion, and subtler joint eversion.

Picture 1 shows the muscle origin and insertion

Picture 2 shows the neutral foot. Notice how the heel bone (calcaneus) is not sitting directly under the leg but off to the outside.

Picture 3 shows how, in foot strike, this orientation allows the foot to pronate, load the posterior calf muscle, and absorb gravity to unload into propulsion.

Picture 4 shows a foam rolling technique to release this important muscle of the foot spring system. This muscle can be particularly sore right below the outside bump below the knee (the head of the fibula).

Self treating this muscle is a great way to prevent injuries and maximize ankle performance prior to working out.

Functional Mechanics of the Pelvis during the gait cycle.

Picture 1 shows a neutral pelvis. This hardly ever occurs as most people have some rotation of the ilium or torsion of the sacrum.

Picture 2 shows the left ilium in stance phase or just prior to push-off and the right ilium in swing phase just prior to heal strike. The left ilium is anteriorly rotated, outflared, and, depressed. The left side of the sacrum is right side-bent and rotated right (Type 2 mechanics). The right ilium is posteriorly rotated, inflared, and elevated. The right sacrum is side-bent right, rotated right.

Picture 3 shows the opposite with the left SI joint closing down and the right one opening up.

These mechanics have a direct effect on the lumbar spine and need to be taken into account when addressing it. Assess and then drive them with the types of treatment and restorative protocols that you use. Leg positions and arm movement are extremely important in doing this.

According to Phillip Greenman DO, 95% of flexed sacral lesions happen on the left side. This is also called "Left on Left" sacral torsion or commonly "Mall Back" from too much shopping. Result is left low back pain, right front hip pain, and right lateral knee pain. It is not a strength problem. The glutes may show up as asymmetrically weak but it is a dynamic positioning problem. Reposition the pelvis before strengthening the glutes.