The best work happens when your mind and your body are in the same place.
There’s no such thing as “purely mental” or “purely physical” work. Writing feels very mind-only and working out feels very body-only, but that’s just not true of either.
Imagine being hunched over a keyboard, dehydrated and tired, trying to write something brilliant. You’ve got all the words in your mind, but the body isn’t there – the body is in the kitchen, in bed, anywhere else. The same with working out: you have the muscles, but if you’re angry, distracted, or upset the workout won’t be as effective, you won’t hit the same goals.
Good balance in your life comes from deciding which one needs to lead the other in any given scenario. Sometimes you need to let the body lead, and the mind has to just accept that it needs to go to the kitchen or to bed or outside or whatever else. Sometimes the body needs to follow the mind, and push through the desire to lay around on the couch in order to get work done.
Find things to do where it’s easy for mind and body to align, and where productive things happen as a result. Do more of those things, and your life will be better.