The announcement that lift was the most important force in propulsion prompted further research.  The most thorough of these researchers was Robert Schleihauf, a coach and engineer.² He discovered the main force of swimming propulsion was the resultant force of lift and drag throughout the sequence of the stroke. (see diagram)

 Lift Coefficient

     The angle of attack, or pitch, of the hand is important in the amount of lift the swimmer achieves.  This is referred to as the lift coefficient.  Schleihauf’’s research shows that the lift coefficient increased until the hand's pitch reached an angle of 40 degrees and then decreased.  This is 20% lower than that of a standard airfoil.⁵

 Drag Coefficient

     Like lift coefficient, the drag coefficient is the relationship of the drag and pitch of the hand.²  Like an airfoil, the more vertical the pitch of the hand, the higher the drag coefficient.  Too large of a drag coefficient can cause a swimmer to lose forward propulsion.
 
     Schleihauf showed that a swimmer uses a resultant force of lift and drag at all times during the stroke to propel forward. (see diagram)  The force in dominance depends on the pitch of the hand.  If the angle is less than 45 degrees the dominant force is lift, at approximately 45 degrees the forces are almost equal, and if the pitch is greater than 45 degrees than the predominate force is drag.⁵ The hand's pitch varies in different places in the stroke as well as from swimmer to swimmer.

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