Thursday, 14 April 2011

The secret to faster swimmimg - cutting drag trumps power.

The secret to faster swimmimg - cutting drag trumps power. Do this by using a high elbow stroke. I'll let Gary Hall(snr) explain here video on Slowtwitch

Text version

How to pull underwater in freestyle.

Many freestyle swimmers might not think they have a choice of how they pull underwater.

"Don't you just stick your hand in the water and pull back?" one might reason. "You mean we have options?"

The reality is that there are huge differences in how you pull underwater with your arm; differences in power and differences in frontal drag. The problem is that as you go from one extreme position to the other extreme arm position under water, you either gain power and drag, or lose power and drag. So, like so many aspects of swimming technique, the underwater pull involves compromise. The question is, which way is best?

First, what are the options? Assuming one does not pull like a grandmother, with the elbow leading the way as the arm moves through the underwater part of the cycle, then one can either pull with the hand/elbow deep (more straight down) which inevitably results in the underwater pull with the hand somewhere underneath the body. In this case, the elbow will bend, but not until the arm has reached a 30 to 40 degree angle with the line of motion and by necessity at this point, the hand goes under the body, while the upper arm points more or less straight down. Because this pulling motion is the most powerful motion one can achieve (positive shoulder angle), it is also the path most often taken (over 90% of swimmers pull this way). After all, if it feels good, do it.

Now, contrast that motion with the motion that most world-class swimmers use to pull underwater. In this case, which represents the other extreme arm position, the pull is initiated not by pulling the arm down, but rather by maintaining the elbow very close to the surface, beginning the pull by dropping the hand/forearm below the elbow (early vertical forearm position). Then, once the hand is nearly directly below the elbow, a quick sweeping motion of the upper arm is made to the side, maintaining the elbow as close to the surface as possible, as the hand finishes the pull and releases. Using this high elbow motion reduces the power one can generate with the pull because it puts the shoulder (at the beginning of the pull) into a negative angle, when coupled with the necessary body rotation. So if this motion reduces power, why does it appear to be preferable to the deep elbow drop? This motion also reduces frontal drag, and in the world of swimming, drag trumps power.

In order to understand how this motion reduces frontal drag, consider the following. First, the magnitude of the drag force is amplified greatly in water over air. Second, the shape and velocity of the object in motion (as well as the medium (water)) largely determine the drag forces. Surface material properties also play a role (shaving, wetsuits and body suits) but aren't quite as important for arm motion. The human swimmer is one of the few objects that drastically change its shape as it moves through the water, mostly as a result of the arm pull. To understand drag, one must first understand what is happening with the motion of the entire arm through the underwater pull cycle.

Today, a world-class woman sprinter will swim 50 meters in 25 seconds, averaging 2 meters per second. How fast is her hand travelling during the underwater pull? Most people think faster. The truth is that her hand enters and leaves the water in nearly the exact same place. In other words, the net velocity of her hand through the entire underwater pull is zero. (It is more complicated than that, but for now let's assume the hand doesn't move). If the hand is not moving forward then it makes no contribution to frontal drag. What about the rest of the arm, how fast is it moving? Well, the upper arm is attached to the body, so that part must also be moving forward at 2 meters per second. As we move down the arm, the average forward speed of the arm gets slower and slower. In other words, the upper arm, which is the largest part of our arm, moves forward (average speed) faster than the lower arm. Both of these features of the upper arm cause it to contribute more to increased frontal drag. The upper arm is the 'bad cop', producing most of the drag. The lower arm is the 'good cop', producing most of the propulsion.

When considering the drag forces that result from different ways of pulling with the arm underwater, one must really concentrate on what is happening with the upper arm, more than the lower arm. It turns out that when one decides to pull deep with the pull, the upper arm gets off axis immediately and the drag coefficient of the swimmer skyrockets. Pulling with the early vertical forearm position keeps the upper arm more in the line of motion of the swimmer at the beginning of the pull. When the swimmer is finally forced to sweep the upper arm to the side for the recovery, the upper arm remains in the unfavorable drag position for a shorter period of time. Remember, tenths of seconds in unfavorable drag positions are enough to nearly stop us in the water.

The truth is that neither way of pulling is ideal, since both cause significant increases in drag. Humans were not engineered well for swimming, so we do the best we can, given our tools. By pulling deep one will increase the frontal drag more, causing the body speed to slow by as much as 50% in going from hand entry to the underwater hand position just in front of the shoulder (slowest point in the stroke cycle). By pulling with the high elbow (early vertical forearm) the speed will still drop during this phase, but perhaps by only 30%.

Pulling with a high elbow not only reduces frontal drag but also helps us obey the law of inertia by not varying our speed as much through the stroke cycle. Whether you feel less strong in the high-elbow position is not as important as the net result - faster swimming and less fatigue. If one practices swimming with an early vertical forearm, one will eventually get stronger in that position, more comfortable with it and improve even more.

To help you get more acquainted with the high elbow underwater pull, we have created a video with some of our favorite drills for learning this technique link

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