Produced, edited, and copyrighted by
Professor Brent S. Rushall, San Diego State University
Volume 4, Number 3: 10 October, 1997


This issue of the Carlile Coaches' Forum is offered as a first step to haul back to reality, the confused and mostly incorrect expressions of thought about technique that are proliferating in swimming cyberspace.

There are several laws of physics and mechanics that cannot be ignored in swimming but seem to be dismissed by some of today's "misinformers." Their relevance to crawl stroke is explained below.

The first is Newton's First Law, the Law of Inertia. If a swimmer was to stretch forward under water, or be in any position for that matter and not apply propulsive force, that swimmer would not continue to progress forward at a constant speed because resistive forces in the fluid would act and cause the swimmer to slow down. So it becomes an important task to apply force as continuously as possible. That means as one arm in crawl ceases to accelerate, or maintain the velocity of the swimmer, it is in the swimmer's best interests to have the other arm commence propulsive forces. The skill aspect is to have as little non-propulsive time between propulsions as possible. A frame from Brooke Bennett's gold medal 800 m race at Atlanta is shown to illustrate this concept. It shows Brooke's right arm beginning to stroke as the left is finishing. There is very little, if any, time in her stroke where propulsive force is not being developed. The inclusion of this picture is not meant to suggest that all swimmers could and should swim like this because other movement principles might take precedence in determining an optimum stroke for other individuals. However, this principle is incontrovertible: If a swimmer does not exert propulsive force, he/she will slow down.

Brooke Bennett

Another principle is that greater speed can be obtained at the end of force application from a long stroke than a short stroke. There is more time to accelerate the load (the non-propulsive body segments -- the head, trunk, a good deal of the legs, and the non-propelling arm). Thus, one has to have the longest "effective pull" possible to achieve the fastest movement of the center of mass at the end of an arm pull. When length of stroke was first scientifically investigated in the 1960s (we did a lot at Indiana University in those days), length of stroke was considered to be the length of propulsive force application, not distance per stroke. I still hold to that concept as being more meaningful and appropriate for competitive speed swimming. Two frames of Kieren Perkins' 1992 world-record swim are included below. They illustrate the commencement of propulsion and its termination. It should be noted that not all movements underwater are propulsive and hence, "the full underwater stroke" is not illustrated.

Kieren Perkins

A third principle is: if a force can be maintained by a circular movement at extremes and direction change stages, rather than stopped, less energy will be used. This is called "rounding out" and when expressed differently is labeled the Principle of Conservation of Momentum. To adhere to this principle one should not straighten the arm at the end of the propulsive push or straighten it forward in a fully extended position (there is a difference between "hard/full" extension with joints locked and "soft" extension with anatomical segments in alignment). In crawl, the recovery forward should be over the water, not slid forward in it (which in turn produces resistive forces that will contribute to slowing the swimmer). With a reach forward over the water the inertia of the arm led by the hand finally dropping into the water can be used to shorten the period of time until a propulsive force can be created. This is what Janet Evans did, what Kieren Perkins did, and what most very successful sprinters do. There are more WR swimmers in FS who do this than those who do not (Sadovyi did not). To illustrate this type of entry, a frame from Alexsandre Popov's gold medal 100 m swim at Atlanta is included. Alexsandre is the swimmer behind Gary Hall, Jr. in this picture.

Alexsandre Popov

It is interesting to note that in analyses of world-record holders and champions the following are true.

  1. The amount of force on a pull is relatively small compared to the amount of lesser swimmers' force production. Distance champions are rarely the strongest force exerters.
  2. The superior streamlining of champions produces less resistance so a smaller propulsive force is required for a particular speed.
  3. The efficiency ratio (total force / resistance) is highest in champions even though the total force usually is less than in non-champions.
  4. The proportion of work created that produces propulsive forces is highest in champions (not all the effort in swimming contributes to propulsion).
  5. The hand/arm does not accelerate in a pull. Rather, it slows down relative to the water and the center of mass is propelled (accelerated) past it. Thus, it is very important to ANCHOR the hand-forearm in the water and feel that one is swimming past that anchor.
  6. Even in champions, at slow speeds there is less propulsive force generated than at racing speeds.
  7. There is an optimal rate and length of effective pull that accompanies a swimmer's fastest swimming. To exaggerate either by lengthening, shortening, easing on force, or accentuating force will lead to slower swimming.

Finally, the sensations at slow swimming speeds, rarely duplicate those of fast swimming. So to "feel" the same way at racing speed as when one is stroking for fewest strokes per lap would be a poor and irrelevant training strategy.

Swimming is such a complicated activity that no one factor can be considered in isolation. Unfortunately, this is how many "gurus/misinformers" talk about swimming techniques. There is a simple explanation for this advocacy. Swimmers are suspended in fluid. Newton's Third Law, which cannot be denied, implies that "to every action there is an equal and opposite reaction." Consequently, when one aspect of technique is changed there will be at least one other aspect that will also be altered in reaction. Sometimes, a change for the good also produces another change for the good and of course some change for a "proposed good" also produces a bad change in some other stroke aspect.

A good index of swimming for use in practical situations is strokes per length at intended race pace swimming speed. When that number is fewest, and that least number can be persistently maintained while consistently swimming repetitions at race pace, then one is in the "ball park" of having the best stroke length.

Please understand that not even this treatment relates all the factors that need to be considered when describing or analyzing any stroke technique. However, these principles are a good place to start for technique rehabilitation and applying verified mechanical factors.

Return to Table of Contents for the Carlile Coaches' Forum.