Plantar flexion allows you to walk down stairs, land properly after a jump and press down on a gas or brake pedal when driving. If you have plantar flexion weakness, these and other normal activities can become difficult. Causes include muscle weakness, an Achilles tendon injury, nerve damage and sciatica.

Achilles Tendon Injuries

Achilles tendinitis (inflammation of the tendon), sprains or tears can all cause plantar flexion weakness. With a complete Achilles tendon rupture, you will not be able to rise up on your toes. Also, if the Achilles tendon is not rehabilitated properly after surgery it can lead to chronic plantar flexion weakness.

Muscle Weakness

The muscles that allow you to flex your foot include the gastrocnemius, soleus, plantaris, peroneus brevis and longus, and tibialis posterior. If you have muscle tightness or trigger points (point tenderness) in any of these muscles, plantar flexion might be affected.

Nerve Involvement

Radiculopathy is a condition marked by the irritation of nerves that cause extremity weakness, tingling and numbness. If it is severe and affects the lower body, plantar flexion weakness may develop. Diabetic neuropathy can also cause foot weakness.

Sciatica

The sciatic nerve starts in the low back area, runs down the posterior of the leg and into the foot. In the case of sciatica, the nerve is inflamed and can cause pain and weakness. Typically it causes weakness on one side of the foot during a plantar flex.

Other Conditions

If you have structural foot abnormalities, a history of ankle sprains or strains, or a tight Achilles tendon, then plantar flexion weakness is possible. Also, Charcot-Marie-Tooth disease (a hereditary illness that affects the extremities) may be the source of your plantar flexion weakness.

Source:

NISMAT: Plantar Flexion Weakness

American Diabetes Association: Muscle Weakness

More Information:

Charcot-Marie-Tooth Association

Mayfield Clinic: Leg Pain (Sciatica)