I do agree with jkenny on the idea of body fat percentage and how it affects a person while he or she is floating. However, I also feel that if you don't know how to keep your body afloat (no matter how muscular) than you are working too hard in the water while you swim.  I have taught plenty of people, mainly older men, how to use their hands slightly by sculling or doing other small modifications so that they can keep their body afloat.  Once a person gets the feel of how his or her body feels when they are floating, swimming comes a lot easier.  If you have any questions please feel free to contact me.

I've coached buoyancy challenged triathletes - the swimmer need to accept their natural aquatic signature in the water and move from there. A patient - now read carefully - TEACHER/coach is a good thing ot have to provide feedback, instruction and confidence during the learning phase