Analysis of the Underwater Pull – Introduction

How the hand and forearm are used to propel a swimmer through the water has been the subject of great debate and controversy since the advent of modern competitive swimming. Prior to 1970, the hand was thought to be analogous to a paddle or an oar for a boat, providing propulsion using Newton’s law of motion. As the hand would move backward in the water, the drag forces created from that motion would result in an equal but opposite reaction: the forward movement of the body.

In the late 60’s and early 70’s, my coach at Indiana University, Dr. James Counsilman, began to study the motion of the hand underwater using strobe lights attached to the fingers of the swimmer in a completely darkened pool. ‘Doc’ would lie still on the bottom of the pool with his scuba gear and his high speed Bolex movie camera, encased in a plastic waterproof housing, and film swimmers such as Mark Spitz, Charlie Hickcox and me overhead. He would then do the same from the side view. From these movies, ‘Doc’ was the first to observe that the hand releases from the water very nearly at the same point as it enters the water to begin each underwater pull. He also observed that the hand moves with considerable sculling motion, from side to side, during the underwater part of the cycle. From this, he deduced that the primary function of the hand/forearm was not a paddle, as previously thought, but rather more of a wing, providing lift. This function obeyed an entirely different law, Bernoulli’s principle, which requires that relative to the arm and hand, the water molecules above the arm are moving at a greater speed than those below. The difference in relative speed of these molecules results in a pressure differential from above and below the arm, creating lift.

Later, other scientists, such as Dr. Joel Stager, also at Indiana University, proved that both theories are correct. The hand and forearm act as both a wing and a paddle, but at different phases of the underwater pull. Much of the side to side motion of the pull, the so-called S pull that ‘Doc’ advocated, is really not beneficial to increasing propulsive power. However, maximizing propulsive power may also not be the most desirable way to pull underwater, as the resultant body speed is related not only to the propulsive power, but inversely related to the frontal drag created by the swimmer’s body and motion of the arms and legs. What makes swimming so challenging is the need to find the right compromise between the motions that produce the most propulsive power and those that result in the least frontal drag.

I have learned more about the mechanics of the underwater pull from a technology called the velocity meter than any other. A few years ago, Dr. Budd Termin came to The Race Club in Islamorada with this technology that uses a Kevlar line attached to the swimmer’s waist. As the swimmer moves through the water, he photographs him/her using four simultaneous stationary video cameras; three from the side and one from the front view. As the Kevlar line unreels, he can then measure the precise body speed at all points during the stroke cycle. For some of the freestyle analysis, in order to understand the pull better, I eliminated the contribution of the kick and isolated the arm and body motions by attaching a pull buoy strapped to my ankles. One of these shots in particular turned out to be very fortuitous as a circular glare spot on the camera lens just happened to coincide almost exactly with the motion of my hand during the underwater pull. From the known length of my arm, I was able to estimate the size of the glare spot projected onto the location of my body to be approximately two feet in diameter. As one views my hand moving through the underwater pull relative to this motionless glare spot, one can also easily appreciate the actual motion of each part of the entire arm and hand relative to the water, that is motionless like the glare spot.

It turns out that if one were to consider that the glare spot were a clock, my hand enters the water at 12 o’clock at the surface and travels nearly exactly around the perimeter of the clock until it reaches 6 o’clock. At that point, the hand cuts inside the quarter of the clock face by elevating toward the center of the clock, and then it proceeds backward toward 9 o’clock. Once the hand reaches 9 o’clock, it releases from the water by following the perimeter of the clock again back to 12, exiting the water almost precisely where it started. In the analysis of this pulling-only stroke cycle, the entire trip around the clock occurs in .85 seconds, while the entire cycle, including the recovery above water, takes 1.1 seconds.

While I am using a shoulder-driven sprint stroke for this example with a relatively high rate of 110 strokes per minute, it serves to demonstrate how the hand and arm are functioning during the underwater pull.

I will use the ‘glare’ clock to divide the underwater pull into four phases; lift, front quadrant propulsion, back quadrant propulsion and release. The lift phase occurs from 12:00 o’clock to 3:00 o’clock. The front quadrant propulsion phase occurs from 3:00 o’clock to 6:00 o’clock. The back quadrant propulsion phase occurs from 6:00 o’clock to 9:00 o’clock. The release phase occurs from 9:00 o’clock back to 12:00 o’clock.

Yours in swimming,

Gary Sr.

4 Responses to Analysis of the Underwater Pull – Introduction

  1. Pingback: Analysis of the Underwater Pull – Phase II: Propulsion Front Quadrant - The Race Club | The Race Club

  2. Humberto

    Dear Gary,
    I have been following your articles and videos on swimming for some time now. I particularly liked your explanation on why the early vertical forearm is so important in freestyle. I was surprised to see a recent study claiming that the deep catch is more effective and faster :
    https://www.facebook.com/FloridaSwimNetwork/posts/1142331819141055

    I appreciate your comments on this.
    Thank you.
    Humberto

     
  3. Gary Hall Sr.

    I have read this study in depth and there are flaws in the study. First, no one today advocates an ‘s’ shaped pull that he studied in the high elbow pull. The hand force should be down and backward. Second, they only measured propulsive forces and lift, not frontal drag forces. While they are correct in their conclusion that a deeper pull produces more propulsion than the higher elbow pull, they failed to study the important factor and that is that the frontal drag caused by the deeper pull is greater than with the high elbow pull. The net body speed of the high elbow pull (without the s pattern) is greater…and btw, Phelps pulls with a pretty high elbow in free with some motion of the hand under the body toward the end of his pull.

     
    • Humberto

      Dear Gary,
      Thank you for the reassuring explanation ! Faith is restored :-)

       

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