Philosophy is mainly linked to existential questions, abstract concepts and metaphysical issues. However, many philosophers (maybe all of them) mentioned, studied and conceptualized the body. Some did it in an attempt to understand the cause behind the being just like the pre-Socratic did by studying nature, the physis; others focused more on the human body.
The body as a philosophical concept is underrated and it deserves our attention to comprehend life, energy and fitness! While the latter is never linked to philosophy, philosophers talked about it in between the lines.
In a round up of this subject, the principal problematic that always emerges about the body is its relation to the mind that you can check in my posts:
On a more personal note, Spinoza and Descartes, although adversaries, taught me how to workout and you can check my posts on both of them:
Finally, why are we so eager to go through difficult physical contortions and put the body through ultimate tests? Check my post on Deleuze’s concept of the body without organs in this post: