Muscle
Cardio-based exercise involves moving at a moderate intensity, using many muscle groups at once. Think: walking, jogging, cycling, etc.
The point of the feminist movement wasn't simply to set our underwear on fire and muscle into small spaces in the male-dominated workplace, but to create a world where the contribution of both sexes was equally valued and no one's worth was judged on their take-home salary.
The imagination is a muscle. If it is not exercised, it atrophies.
Nothing stops the man who desires to achieve. Every obstacle is simply a course to develop his achievement muscle. It's a strengthening of his powers of accomplishment.
A muscle is like a car. If you want it to run well early in the morning, you have to warm it up.
Write every day. You don't have to write about anything specific, but you should exercise your writing muscle constantly.
You have a right to say no. Most of us have very weak and flaccid 'no' muscles. We feel guilty for saying no. We get ostracized and challenged for saying no, so we forget it's our choice. Your 'no' muscle has to be built up to get to a place where you can say, 'I don't care if that's what you want. I don't want that. No'.
If you do not use a muscle or any part of the body, it tends to become atrophic. So is the case with the brain. The more you use it, the better it becomes.