I'm a guy with longish hair (curly and shoulder length). I run long distances (50-ish miles a week) and bike commute daily.

I also shampoo only 2 or 3 times a year. No issues for me. I just use very hot water and really rub my scalp in the shower. Started it as a 30-day experiment in 2010 when I had bad dandruff and never looked back.