Analysis of the Underwater Pull – Phase II: Propulsion Front Quadrant

At the point when the hand reaches 3 o’clock on the ‘glare’ clock, the distal part of the arm and hand change functions. They stop acting like a wing and/or applying downward force for lift and suddenly change directions and accelerate backwards. For approximately the next 1/3 of a second, the hand (and forearm) will create a propulsive force by moving in the opposite direction for a distance of approximately two feet and that motion will help drive the swimmer forward.

The amount of body speed that is generated by this propulsive phase of the underwater pull is related to the effective surface area of the pulling arm/hand, the speed or acceleration of the hand/forearm as it moves backward and the amount of force generated by the counter-rotation of the body. The body speed is also inversely related to the amount of frontal drag created by the ever-changing shape of the entire swimmer throughout the pull cycle.

I often ask my campers the question of whether the power of the arm pull is greater in the front quadrant or the back quadrant, separated anatomically by the shoulder. I would say that the responses that I get are about half and half, which is to say that at least half the people don’t know the answer. The others are probably good guessers.

Since the propulsive phase begins when the hand is at the 3 o’clock position, the hand is then situated in the front quadrant, about one foot in front of the shoulder. By the time the hand reaches this point, two important things have happened. First, as the body counter-rotates in the direction of the pulling arm, the arm has moved from an extended position (negative angle) of the shoulder joint to initiate the lift phase (using a high elbow position), to a flexed position (positive angle) to initiate the propulsive phases. The flexed position of the arm/shoulder joint puts the arm in a much greater biomechanical position of strength than the extended position. Second, the rotation/counter-rotation of the body requires that the rotation of the body starts slowly, accelerates to a faster speed, then it slows again to a stop, before rotating in the opposite direction. The greatest amount of counter force that is generated by this rotational motion occurs in the middle when the rotational speed is greatest. This also coincides with the hand propulsion in the front quadrant moving from 3 o’clock to 6 o’clock. The greater the counter force, the more power we can generate from the arm pull.

The biomechanical strength of the arm not only changes as the body counter rotates, but also as the hand moves from 3 o’clock, a position about a foot above the shoulder, to 9 o’clock, when the hand is closer to the hip. When the hand begins this propulsive journey at 3 o’clock, it starts out with the highest level of strength, engaging arm, shoulder, back, chest and core muscles. By the time it ends the propulsive journey at 9 o’clock, close to the hip, the tricep muscle is just about the only muscle still working. Most of the others have all dropped out.

If one were to try to equate body speed to power of the underwater pull, it would be easy to believe that more power is generated in the back quadrant because the body speed (in my example with arms only) increases from 1.39 m/sec at the 3 o’clock position to 1.58 m/sec at the 6 o’clock position to 1.71 m/sec at the 9 o’clock position. In other words the further back my hand gets, the faster I am going. However, body speed is not just determined by the power of the underwater pull. It also depends on frontal drag and most of that extra drag is being contributed by the upper arm moving forward during the entire front quadrant phase. By the time the hand reaches 6 o’clock and enters the back quadrant, the elbow gets tucked into the side quickly and the upper arms stops contributing to frontal drag, as it begins to move backward slightly.

For both of these reasons; greater biomechanical strength in the front and maximum rotational body speed in the front, I believe most of the power of the arm pull is generated in the motion within the front quadrant from 3 to 6 o’clock, rather than in the back quadrant, from 6 to 9 o’clock. So the next time your coach tells you to push your hand out the back, think twice before you do it.

Yours in swimming,

Gary Sr.

One Response to Analysis of the Underwater Pull – Phase II: Propulsion Front Quadrant

  1. Pingback: Analysis of the Underwater Pull – Phase I: Lift - The Race Club | The Race Club

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