Type 4 (kinky and curly) hair doesn't get greasy as badly and as quickly as straight hair does for the very reason that it is kinky or curly.
Why greasiness is not an issue
Sebum, the natural oil produced by the scalp struggles to move up the kinks, curls and coils of type 4 hair. This means that dryness is much more of a problem for curly and kinky haired types than greasy hair and overwashing just exacerbates the problem.
Tangling is a big issue
The washing process is prime time for hair to get tangled and knotted.
- The shorter your hair is the more often you can wash it because it tangles less.
- The longer, thicker and more curly your hair is, the less you need to wash it because it tangles a lot more (it also takes longer to get greasy)
But I go to the gym a lot?
Personally my hair doesn't take on a stench when I exercise even when I sweat heavily so I just stick to my weekly wash. I frequently make one of my workout days coincide with my wash routine.
Of course, your hair's moisture level, tendency to get knots and tangles and sweat pattern will be different to mine so you need to find the right wash-regularity for you.