DRAG FORCES ARE LARGE IN CRAWL STROKE PROPULSION
Wood, T. C. (1988). A fluid dynamic analysis of the propulsive potential of the hand and forearm in swimming. In J. Terauds & W. Bedingfield (Eds.), International series on sport sciences, SWIMMING III, Vol. 8. Baltimore: University Park Press.
One of the major controversies over the years has been whether a swimmer derives propulsive force through lift or drag forces. In recent years the tide of opinion has leaned toward lift forces, a principal justification being the curvilinear movements of the hand (e.g., the "S" pull). It is known, but not widely, that the deviating tracking of the hand and forearm is associated with movements counteractive to rotational forces generated elsewhere in the body and in the symmetrical strokes with anatomic and physiological considerations.
This study analyzed the fluid foil characteristics of the hand and forearm modeled from an elite swimmer. Several conclusions were reached: 1) both lift and drag forces were recorded across the hand and forearm; 2) at all velocities, maximum drag forces were vastly greater than lift forces across the ulnar and radial borders (the borders that are used during the acceleration phases of swimming); and 3) at all velocities, maximum drag forces were only slightly greater than lift forces across the distal border (from the finger tips on up the arm as when the arm enters the water in freestyle and butterfly).
Implication. It is an oversimplification to speak of the hand pushing water backward or searching for still water, or of fixing the hand against the water. The opportunities for making full propulsive use of the possible maximum form drag forces are restricted because of existing stroke patterns and anatomical constraints which prevent the hand and forearm being used perpendicular to the swim line. Thus, swimming is a subtle change of balance between drag and lift forces but in the acceleration phase of most strokes the greater contribution comes from drag forces. This means that swimmers should be advised to accentuate the feeling of pressure on the forearm and hand in a backward direction even though the path of movement might not be directly backward. With that emphasis there will be minor modifications to the pitch of the hand (it will not be perpendicular to the swim line). That occurs as a compromise between a swimmer's anatomy and the particular stroke being performed.
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