Several forces play significant roles in the movement of the human body through the water.  The forces are drag, lift, gravity and buoyancy.  Lift and drag are the main propulsive forces that are used by swimmers.  Resistance, known as drag, can be broken into three main categories: frontal resistance, skin friction, and eddy resistance.  The effect of buoyancy in swimming is best described by Archimedes’ principle: a body fully or partially submerged in a fluid is buoyed up by a force equal to the weight of the fluid that is displaced by the body.¹ This effectively negates any effects that gravity might have on a swimmer.  The rare exception to this is a swimmer with very little body fat, and this is overcome by keeping the lungs inflated to a certain degree at all times.