This guide is not aimed towards communists specifically -- the principles apply to everyone similarly. However, arguments can be made as to why a guide on a communist encyclopedia is important and interesting:
Many comrades want this information, but do not know where to get it. In this way we are bringing it to them if they happen to read ProleWiki.
The fitness industry is dominated by reactionary content and personalities. With this guide, you are sure it was written by a communist and will not contain unwelcome anecdotes.
And of course, fitness is important to all communists for a variety of reasons.