Running can make your whole body ache, but that's to be expected. When you feel a sharp pain in your foot, though, it can sideline you — and who knows for how long.
When the inside of your foot hurts from running, it's probably due to the posterior tibialis tendon, a little-known but very important body part for runners. It helps flex and invert the ankle, rolling it inward, as well as supports the arch of the foot. It's a tiny little tendon — no thicker than the size of a pencil — but you'll definitely feel it when it's irritated or strained.
Read More: Remedies for Sore Feet From Running
Testing the Tibialis
First, you will want to make sure that it's posterior tibial tendon dysfunction — also known as posterior tibial tendinitis — with which you're actually dealing. A single-leg heel raise will help you determine that.
To test it: Stand on the affected leg, lifting the other one in the air, so you're balancing. Use your calf muscles to rise up onto your tippy-toes. Lock your ankle at the top.
If you feel pain on the inside of your foot, you have posterior tibial tendon dysfunction.
Treating the Pain
First things first: Stop running. You need to give your foot some rest. That doesn't mean that you have to cease exercising entirely; you should just do an activity that doesn't put a lot of pressure on your foot, such as swimming or biking.
Beyond taking a break, you can ice the affected area for 20 minutes at a time, three to four times a day, particularly if it's swollen. This will help reduce the inflammation of the muscle. An NSAID, such as ibuprofen or naproxen will also help decrease the pain.
If it's been a month, and you still can't run, it's time to head to the doctor. In the worst-case scenario, you can be fitted for walking boot or short cast for six to eight weeks, forcing the muscle to get the rest it needs.
The tendon probably started to hurt because you ramped up your training too quickly or intensely. When you're looking to increase your distance, keep it to a 10 percent jump every week. In other words, if you're running 10 miles this week, only increase it to 11 miles the following week.
When you return to running, start at a slow pace and run on even, flat terrain. Hills or trail running can re-injure your foot fairly quickly.
If you find that the posterior tibialis tendonitis comes back frequently, look into adding an orthotic to your running shoe. The foot control can help with your running gait, which decreases irritation to the tendon. You might be able to get away with an over-the-counter variety, but a visit to the physical therapist can also help you with a custom orthotic.