Courtesy of Gary Hall Sr., 10-time World Record Holder, 3-time Olympian, 1976 Olympic Games US Flagbearer and The Race Club co-founder.
Propulsive Forces & Frontal Drag Forces
Sir Isaac Newton’s three laws of motion are as applicable today to a swimmer as they were centuries ago when he formulated them. However, for me it is easier to conceptualize the application of the three laws by separately considering the forces that move us through the water (propulsive forces), the forces that slow us down (frontal drag forces) and the law of inertia, which tells us it is most efficient to maintain a constant speed by keeping the forces of propulsion and drag equal.
Axial Rotation
The propulsion of a swimmer is derived primarily from two sources, the hands and the feet. However, there is another motion involved in the freestyle and backstroke of a fast swimmer, other than kicking and pulling, that is vitally important to generate more propulsion; the axial rotation of the body from side to side.
Freestyle & Backstroke
Although coaches and swimmers commonly believe that one of the reasons fast freestlyers and backstrokers rotate their bodies along the axis of their motion is to reduce drag, I don’t agree. If that were true, we would see a substantially faster kicking speed on our sides than we do on our stomachs or backs, and that is simply not the case.
Another common theory for why we rotate our bodies in freestyle and backstroke is so we can reach out further on each stroke. While that may be true at the finish of a race (particularly freestyle), I don’t believe the extension of the arms on the recovery of a rotating swimmer is any further than on a non-rotating swimmer.
Mechanical & Biomechanical
There are two reasons for rotating the body during freestyle and backstroke. One is mechanical and the other is biomechanical. The biomechanical reason is that by rotating our body to initiate the underwater pull, we put ourselves into a more favorable position to use our back muscles, particularly the large latissimus dorsi muscle. That will make our pull stronger.
The mechanical reason is that by counter-rotating our bodies during the underwater pull we can create a significant force to pull against. In other words, we are no longer pulling against just water molecules that are relatively motionless. We now have the water, plus whatever force we can generate with the counter-rotation of our body. The amount of that force that we get to pull against is related to our mass (weight) and to the angular velocity of our body’s rotation (how fast we rotate).
The rotation of the body doesn’t just happen. A swimmer has to make it happen and that requires a lot of core strength and work. When the rotation is fast and timed well, it is worth the effort, creating a substantial force that enable the swimmer to cover more distance with each stroke.
No one said swimming fast was easy. Here are some of our favorite drills:
http://www.theraceclub.com/videos/secret-tip-how-to-pull-underwater-drills/
Gary Hall, Sr., Technical Director and Head Coach of The Race Club (courtesy of TRC)
Yours in Swimming,
Gary Hall Sr.
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I’ve never agreed with the view that you get more reach at the finish by rotating. Yes, it’s a good way to get kids to reach out for the finish but in actual fact the position of your body is purely down to the perspective of the viewer. I’ve seen so many coaches on poolside reaching up and then showing “how much further they can reach when they turn side ways”. Well, like I say it all depends on where you’re looking at them from.
When you rotate, you get more reach which results in more glide and more power through the stroke.
Reach vs Pull
Hi Gary, love your articles.
I teach kids swimming and am attempting to establish ‘my teaching philosophy’ on these sometimes conflicting areas. Your thoughts or information most appreciated.
‘which tells us it is most efficient to maintain a constant speed by keeping the forces of propulsion and drag equal’
https://www.youtube.com/watch?v=e4iO34K1Ufo
http://www.swimsmooth.com/catch.html
Reading, looking, trying………ha will never everything…..BUT would like to attain a standard of excellence for my swimmers.
Cheers
Michael
“Although coaches and swimmers commonly believe that one of the reasons fast freestlyers and backstrokers rotate their bodies along the axis of their motion is to reduce drag, I don’t agree”
I’ve never heard any coach claim that rotation is intended to reduce drag. Is this a common belief? When I started coaching I was taught that it was to increase propulsion. The headline seems to allege that this is a radical theory, when in fact it’s fairly common knowledge in my experience.
In my experience, coaches often tell swimmers to do the right thing…but for the wrong reason. Body rotation is a good example. I have heard many coaches and swimmers state that body rotation should be done to reduce frontal drag…but not to augment propulsion. It sounds like you had a good teacher.
Had a lot of people express this but Bill Boomer was the coach who clearly stated it in a way that carried the most impact and clearly laid out the scientific principals. 🙂
The coupling motions we are referring to are extremely common. We use them every day…swinging the arms while walking, rotating the body during a golf swing, moving the legs during the long jump. I just don’t think many people have recognized just how powerful these coupling motions are and how they can augment propulsion and speed. Bill Boomer apparently gets it.
Really enjoying the race club swim drills. As a lead coach at a club for younger to older swimmers I can adapt the drills and being a massive yoga fan too. Glad you agree it goes hand in hand with swimming. Wonderfully presented and great descriptions throughout.
Is anyone familiar with the freestyle technique taught in the IKKOS program? I ask this because our team is using IKKOS for stroke technique. It seems the more IKKOS lessons, those swimmers are now swimming a straight arm freestlye, with arms swinging to the sides over the water. To me, it does not look as effective as a traditional stroke.
I’m curious what is on the video in the IKKOS goggles as I haven’t seen it myself and my swimmer cannot articluate it. Is this program teaching effective stroke technique? Thoughts?
Thanks!
There are two important coupling motions in freestyle that increase propulsion. One is body rotation and the other is the arm recovery. The amount of kinetic energy in those two motions is proportional to the square of the angular velocity (speed of the rotation or stroke rate) and the square of the radius. With the arm recovery we can change both angular velocity and radius…yet with the greater mass of the body compared to the arm, its rotational speed is the most important coupling motion.
With a low swinging straight arm, the kinetic energy of the arm may be high, but body rotational speed is sacrificed. Ideally, one wants both body rotation and high energy arm recovery. That is… Read more »
Very interesting Gary! Can you define “coupling motion”?
Also, you really have the technical aspects down…just curious how you know all of the technical details – besides your experience of course! 🙂 – what did you major in college or study thereafter, is this Physics or ?? A friend of mine’s father was a professor of sports kiniesology (sp?) with specialty in swimming (he was also an Olympic swimmer long ago) – is this the field? So interesting!
The mechanical reason Mr. Hall explains and seems to cause some confusion, can be maybe most easily visualized or explained by making a comparison to a bullet. All firearms are nowadays design in a way, that a bullet leaves the barrel spinning.
This spinning motion does not increase the speed of the bullet, however by creating a centrifugal force it increases the energy of the bullet making it more stable and thus flying further.
Same applies to the rotating body of a swimmer. The rotation creates a centrifugal force which increases the energy of the moving body. This does NOT however translate automatically into faster swim speed nor does it increase the power of the pull.
What it does do… Read more »
A great discussion!
To GermanEngineer – Your explanation is a great one, with “rifling” of a gun barrel and the development of an oblong bullet definitely makes it fly further and generally straight. Using the spinning top analogy is also a good one except I don’t feel that a swimmer is rotating fast enough to create the angular momentum effect of a spinning bullet or a top.
Consider that the actual propulsive forces generated by the pulling arm are really not that great.
There have been very many studies old and new that have shown peak pulling forces in freestyle at 80 to 100 newton’s or about 18 – 22 lbs. of force. Not very high. In… Read more »
As Mr. Hall mentioned in his article, the rotation has no or only minimal effect on the drag the body faces. And of course it is always more beneficial trying to decrease drag, as that contributes to the overall efficiency.
You are right about a deep pull creating more drag than a shallow pull, however the body rotation does not automatically create a deeper pull. It is very well possible to swim with strong rotation and connect it to a high-elbow catch and shallow stroke.
As to your doubt about the amount of angular momentum created by the rotating body compared to a bullet or a spinning top, you have to take into account that the rotating body of a… Read more »
????
The issue with rifling has to do with conservation of angular momentum. If you add rotation about the long axis of the bullet, with the corresponding angular momentum pointing along the axis (parallel or antiparallel, depending on the sign of the rotation), then small perturbations due to air currents, etc., will have a minimal effect on the direction that the bullet goes, thus increasing accuracy. However, I don’t think in swimming this is relevant because the speeds through the water are so small and the viscosity of the water so large in comparison to the bullet. I also question the idea that rotation can create additional propulsion, unless this causes the water to have a momentum component along the direction… Read more »
I would like to tackle a couple of things that I’ve read here and hopefully break this down into something slightly easier to understand.
First off, I think Gary Hall Sr. is right about rotation giving us more force (sort of), but first, let’s analyze how we actually go forward in the water in a very simple way.
In order to go forward, we must push water backwards. It sounds simple, but has complicated components. Start from the bottom up with the kick. We push against the water with the front of our legs at an angle, which has then two components, a downward component and a backwards component (for more on that google vectors). The downward push lifts… Read more »
I think you’re overlooking that different parts of the arm move at different speeds. Your hand may remain stationary in the water, but the higher parts of your arm will be dragging (the higher the part the more the drag).