When it happened to me, I couldn’t find any information on Google to address it, so maybe this can help someone.
I had a problem with my shins when running. My shin muscles, the tibialis anterior, tightened up and became rock hard (and painful) every time I started a run.
The pain and tightness, unsurprisingly, made leg extension difficult and affected my stride. Oddly, after 5 miles of running with throbbing shin muscles and occasionally walking, the muscle would finally relax, permitting normal running.
Surveying the literature for a solution didn’t help. It turns out a lot of things can go wrong with shins and they are all lumped under the one category of ‘shin splints’. Imagine a world where everyone was named Bob. That’s kind of how it is with shin problems. The most promising explanation was that the muscle was weak. Unfortunately, the cure did not work. Performing strengthening exercises only made the muscle seize up tighter and throb harder during runs.
Finally, an ‘aha’ moment. While tracing the alphabet with my toes (one of those strengthening exercises), I realized that the shin muscle were under tension and pulled back whenever I fully contracted my calf muscle. During the last third of the movement, both muscles pulled at the same time. No wonder my shin muscles tightened up when I ran! The shin muscle resisted the calf muscle with every step and worked itself to exhaustion through eccentric contraction. No amount of strengthening was going to help. In fact, more strength meant more opposition to forward movement and more wasted energy. This was a problem with flexibility, not strength.
In the end, the solution to my problem was to make the shin muscle flexible enough that it would not engage while the calf muscle was contracting. Now, before and after every run, I sit on my heels for 20 seconds with knees pointed forward and toes pointed backwards. That’s all. That’s all it took to eliminate miles of running with throbbing shin muscles.