Mental!

Mental Strength is the ability to concentrate when you want to, as hard as you want to, for as long as you want to. 

Mental Flexibility is your capacity to switch from one mode of thought to another. It's a playful process as you toy about, find new combinations, and look in new directions. Mental Flexibility is artistry, holistic thought, creativity, brainstorming, and a bit of Zen, all rolled into one. 

When you want to put your ideas into action, you need Mental Endurance.

Mental Staying Power is the ability to sustain an increased level of activity without getting distracted or discouraged. It's the capacity to persist, to go the full mile. 

And when you want to add precision and flair, you need Mental Coordination.

Mental Coordination is timing, balance, and agility. It's the knack of gracefully orchestrating your thinking so that you can deal with several things at once, keep balanced within the face of uncertainty, learn for knowledge's sake, and strive for higher ideals. 

 It's these four basic qualities — Strength, Flexibility, Endurance, And Coordination — that make up a fit mind. Only by stretching, flexing, exerting, relaxing, moving your mind in different ways, performing different mental movements, does your mind get in shape.