This post and its parent post is a good conversation on using principles of physical fitness to improve one's writing. I wanted to add one final thing on though from the physical world. Nutrition.
Without nutrition, progressive overloads, higher weights, etc, cannot do anything, and in fact will eventually become impossible to do in the first place due to atrophy.
And in writing there is also a nutrition aspect. I think the closest thing to nutrition is a fulfilling life. Often when I can't think of something to write, it is not because of some type of technical writer's block, but more a mental life block. I am not living in a way where my truest emotions are able to pass through from my memories into my front ponderings. And so it's like my ideas and perspective are constipated.
The reasons for this vary for others, but for me it has always been caused by not living the type of life I need to be living, while at the same time keeping myself busy with nonsense to sustain the lie.
So great ways to improve writing based on principles from the world of physical fitness - nutrition == fulfilling life.