The flexor hallucis longus muscle attaches from the calf to the big toe. Problems there are often called ‘dancer’s tendonitis’ , as the repeated rélevés and pushing off of the foot. Of course, dancers aren’t the only ones that can have problems here, gymnasts, sprinters and swimmers (who push off from the blocks) can have challenges with this muscle.
It is an important controller of pronation and supination at the midfoot and helps to transfer force from the rear foot to the toes. It is underneath the soleus muscle and I suspect that weakness and/or tightness in one muscle influences the other.
Here is an excellent article on the FHL and athletes with great illustrations.
This area has been compromised on my right foot due to a sesamoid injury about 20 years ago. (those are the 2 tiny bones underneath the base of the big toe) My rélevé on that foot has been compromised. I simply can’t get up as high as I could before. The mobilization that I’m going to show you below has been very helpful.
While I do not expect to get my full rélevé back, I do want to maintain normal gait and the ability to roll through the foot correctly. If you have a ‘stiff’ big toe area give it a try! Of course, it goes without saying that you shouldn’t feel any pain while doing it. There can be other reasons for your big toe not flexing as well anymore that have nothing to do with the FHL. This is just an exercise to explore and see if it is helpful!
To your success!