FORCES IN SWIMMING -- A RE-EVALUATION OF CURRENT STATUS: PART II
The intention of this paper is to clarify the foundational principles involved in both propulsion and resistance in competitive swimming. Currently, there are controversial issues surrounding the bases of propulsive forces created in the four competitive strokes. Initial incomplete descriptions of those forces are still popular. The impact of types of resistance on swimming speed is not well understood. The clarification of these topics should produce better understandings and hopefully, more effective coaching.
This review does not dissect each competitive stroke or explain techniques. It only covers the theoretical bases of force production and the nature of resistances. More detailed explanations of technique will have to remain for another forum.
An Historical Perspective
In the 1950s and '60s, James "Doc" Counsilman and Charles "Red" Silvia applied principles of mechanics primarily to the propulsive forces of competitive swimming strokes. In the early years, descriptions of actions were related to what was observed in swimming actions by champion swimmers. Some credence was given to Newton's Third Law of Motion, "To every action there is an equal and opposite reaction", which accounted for drag forces, as being the theoretical basis for propulsive forces. However, in the late 1960s, Counsilman proposed that propulsion was gained through "lift" rather than drag force. The basis of that force was Bernoulli's Principle (Counsilman, 1970, p. 3). At this time Silvia continued to interpret forces in competitive swimming strokes as being derived from Newtonian Laws, that is, when force is applied backward, a swimmer will be propelled forward (Silvia, 1970).
"Doc" Counsilman was possibly the most profiled coach/scientist in swimming during the 1960s and '70s. His charismatic and personable nature, remarkable successes as a coach, and his logical academic exposition of swimming training and techniques created his reputation as a very credible source of information and knowledge. "Red" Silvia, equally impressive in personal and academic qualities, was not as high-profiled and so his "teachings" were not as universal as those of Counsilman. Both men impacted swimming research, particularly through the pragmatic evaluation of the stroke patterns of champion swimmers. However, it cannot be denied that Counsilman's pronouncements were accepted faithfully as being true and accurate. Others also contributed to swimming knowledge at this time, but Silvia, and in particular Counsilman, were the main theorists of the period.
Counsilman's effect on persons in swimming was remarkable. His popularity as a teacher at Indiana University meant that he was able to educate many receptive students about swimming mechanics. His very frequent worldwide clinics and his swimming camps added to his fame and profile. However, it is possibly his book "The science of SWIMMING" (Counsilman, 1968), the most published and translated text on swimming, that established him as the "world-authority" on swimming.
In "The science of SWIMMING", Counsilman described propulsive forces on the surface of the hand being created in a similar fashion to those on the surface of an oar--that is, a drag force is created as a direct application of Newton's Third Law. The direct force was not reconciled with the curved paths of actions observed and reported in swimmers and frequently referred to as S-shaped or "inverted question mark" pulls (Counsilman, 1968, p. 52-53). Resistance was described solely as a quadratic relationship to the speed of the swimmer ("The theoretical square law", 1968, pp. 16-17).
However, in 1969, Counsilman committed himself to a radical change in the theoretical basis of propulsive forces in swimming. He proposed Bernoulli's Principle as the explanation of those forces. His followers were very quick to adopt this stance and conclude that "lift" forces were the major forces that produced propulsion in all competitive swimming strokes. For a brief time, "lift" was considered the only force for propulsion. However, as the limitations of sole lift explanations became apparent, "drag" forces (of Newtonian origin) crept back into the propulsion equation. Without any empirical evidence, but rather by intuitive analyses, "researchers" analyzed strokes of swimmers promoting lift forces as being the predominant propulsive force. For example, Schleihauf (in Counsilman, 1977, pp. 232-247) attributed the primary value of drag forces as being "The drag component of the hand could neutralize eccentric kicking forces and the lift component could approach its maximum value" (Schleihauf, 1977, p. 239). Such a position was echoed by Barthels (1982): ". . . proposed the ideal condition of maximizing the propulsive force and minimizing propulsive drag" (p. 386). Many persons, particularly those outside of the USA, appeared to become enamored with the Bernoulli's Principle explanation of propulsive forces and persist with it today (e.g., Swimming Coaching Accreditation Scheme, Australia). Counsilman did modify his initial exclusivity of lift force being the only force in propulsion. Over time, he talked more of hand pitch ("angle of attack") as a significant determinant for creating force but never really focused on drag force as a major determinant of propelling efficiency. He continued to emphasize a sideways orientation of stroke movements in the S-shaped or hourglass pull as facilitating lift and therefore, producing the forces to create speed in swimming.
As with any good science, attention often turns to the objective verification of theories that are postulated. Larry Holt and his students at Dalhousie University in Canada, initiated detailed evaluations of the forces created by the hand and forearm in strokes other than breaststroke. Direct measurements, believed to be the first conducted, showed that at only some stage of an arm pull is the swimmer propelled or accelerated by the arm action and that during the propulsive phase it is drag force that is the major contributor among the forces created. Holt's work remained buried in relatively obscure scholastic books that were published some years after their completion (e.g., Valiant, 1981; Valiant, Holt, & Alexander, 1982; Wood, 1977; Wood & Holt, 1979). The pioneering works of Holt and his students will be discussed in more detail below.
The popularity of Bernoulli's Principle as being the theoretical basis for swimming propulsion continued through the years. It was adopted by noted authorities such as Jim Hay in biomechanics (Hay, 1993) and Ernest Maglischo (1982, 1993) in swimming. The longevity of the blind acceptance of the "Bernoulli-Principle-explanation" for propulsion in swimming will remain a discussion topic in the history of sport science far into the future.
Very recently, the description of the arm actions of all swimming strokes has taken a great leap forward due to the work of Jane Cappaert at US Swimming's International Center for Aquatic Research (ICAR) in Colorado Springs. Objective analyses of the stroking patterns of gold medallists during finals races at the 1991 World Championships in Perth, Australia, and the 1992 Barcelona Olympic Games have been produced. The previous research weaknesses of describing what happens when elite swimmers perform in training swims and inferring those movement patterns to competitive performances plus restrictions to two-dimensional views of swimming, have been removed. The scientific value and accuracy of Cappaert's work has been independently verified by personal visitations of and assessments by a number of scientists during the ICAR review in 1993. Cappaert has drawn attention to the production of both lift and drag forces in the development of propelling efficiency in all strokes. Only in breaststroke, do lift forces exceed the importance of drag forces during propulsion. Independent of Holt's and Cappaert's work, Sprigings and Koehler (1990) at the University of Saskatchewan, questioned the appropriateness of trying to use Bernoulli's Principle as the model to explain the lift phenomenon. They pointed out that both lift and drag can be better understood using Newton's Second and Third Laws as the predictor model.
The consideration of what forces slow a swimmer's forward movement has received less attention. It is very possible that minimizing the resistances created in movements could allow swimmers to improve in swimming speed. In 1933, Karpovich described resistances of swimming as being skin friction, eddy resistance, and wave-making resistance. The details of that delineation have been lost over time. Most considerations of resistance have revolved around active and passive resistance (e.g., Chatard, Laddie, Bourgoin, & Lacour, 1990). Sheehan and Laughrin (1992) improved on the theoretical considerations of resistive forces involved in moving through a fluid medium by reviving and refining Karpovich's categories. Their work allows a more detailed consideration of actions and their resistance effects in swimming strokes.
The actions, proposals, and researches indicated above are considered to be "landmark" activities in the development of understanding forces in swimming. They will serve as the basis of describing the current status of the topic. It is recognized that others have contributed to the knowledge of swimming but it is not possible to produce a complete anthology of all authors' works in this forum.
Go to the next section, PROPULSIVE FORCES, of this article.
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