Swim Training: Rethink Rotation in Backstroke and Freestyle

  14 SwimSwam | July 12th, 2014 | Featured, International, Opinion, Training, Training Intel

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)

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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Comments

  1. sprintdude9000 says:
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    “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).”

    I don’t understand what this means, can someone please explain?

    • Sven says:
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      I’ll give you my interpretation, but I can’t promise it’s 100% right. Hell, I could be totally wrong.

      Basically, as your left arm is pulling back and your left shoulder is digging down and back, your right arm is swinging up and your right shoulder is coming up and forward. That opposition gives the right side of your body some forward momentum, taking some of the weight of your body off of the water held by your left arm. If all of your weight is being applied only to the water, your hand will slip back through the water more instead of anchoring and pushing the body forward from that anchor. By giving the body more forward momentum at the same time as it applies force backward, we get more out of that pull since the hand will catch and anchor better.

      Also, think about the third law. If we have good opposition, timing, and connection between the shoulders then the upward and forward motion of the right arm, while not inherently propulsive, would add force to the backward motion of the left arm (equal in magnitude, opposite in direction).

      I would say that timing is the key to effectively using rotation. While some coaches tend to take a more-is-better approach to rotation, we see much flatter strokes in the elites. With younger, less skilled swimmers, increasing rotation would make sense. Increase the duration/magnitude of rotation and the timing becomes easier to manage. As timing improves, decrease rotation to increase turnover and power, until you have backstrokers rotating just 30 degrees as we see now. They rotate just enough to benefit them, and then go back for another stroke.

      Sorry for the reply, I hope I didn’t go too far beyond the scope of your question.

      • SprintDude9000 says:
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        Hi Sven – I understand what you are saying but don’t think it’s what Gary Sr. is talking about. Thanks anyway though!

        It’s the following two sentances in particular that are causing me confusion:

        “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.”

        • Barb Samuel says:
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          What I got from it is that we will be in a body position to create momentum by the use of how the water will flow, and body position. Like an aerodynamically designed car uses air flow to improve performance and speed.

    • Nate says:
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      I’m a physics teacher and swim coach and this is my best interpretation so far:
      Where Hall is most expressive about what he is talking about and at the same time most enigmatic is the sentence: “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).” This suggests that he is talking about our body’s rotational momentum, which comes from those two factors. The only way I can figure that rotational momentum and the force of the hand pulling through the water can interact is through the torque done by the pull which actually lifts the upper body up out of the water (if you don’t believe me, try laying on your side in bed and doing a freestyle pull). The result of the interaction between the torque and your rotational momentum is that the body fish tails a little toward the pulling arm, an effect we coaches see all the time in our younger swimmers with weak cores. So, if Coach Hall is saying what I think he is saying it is that when swimmers develop the core strength to resist that fish tail effect, the force that would have pushed their hips to the side can instead somehow be harnessed in moving forward. How? I’m still very unsure and too tired to tackle that question tonight.

  2. Barb Samuel says:
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    Thank You for this fantastic article that confirms for me the efforts I have been making to improve and develop my rotation. I am saving this, to watch the accompanying videos and look forward to much improvement in my movement and speed through the water.

  3. coachkopie says:
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    Some thoughts:

    * We swim these strokes side to side but we do not get to or ever swim on our side. the actual rotation is modest although it is helpful and vital.

    * The top side arm recovers in a curvalinear fashion and acts as a throw weight

    * The bottom side hip rotates longtitudinally enough to “get out of the way” of the recovering arm to allow for a quick, rhythmic exit coupled with a quick, rhtyhmic entry of the forward entering that drives INTO the water.

    Power and sustainable stroke rate come from rhythm and flow. Have a safe day.

  4. SprintDude9000 says:
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    >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.

    Surely rotating allows you to pull deeper (mid-stroke) and therefor increase torque?

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      Body rotation does tend to facilitate a deeper pull, which does create more propulsive force and torque at the shoulder. Unfortunately, that is not a good thing. Because the deeper pull also creates so much more frontal drag force, a less powerful high elbow pull results in a faster body speed. Using a lot of body rotation with the high elbow pull is tricky, requiring a lot of shoulder extension to do correctly, particularly at the initiation of the pull. The high elbow pulling motion is neither intuitive nor obvious to swimmers. I call the deep pull the ‘power trap’.

  5. Catherine says:
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    Barb, it makes sense to me that rotating to the side would decrease drag but I don’t think that’s what this article is saying.

    Here’s my interpretation:
    One sentence says “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).” That sentence is talking about a torque, which would be side to side at best and give no propulsion. The previous sentence says “We now have the water, plus whatever force we can generate with the counter-rotation of our body. ” If you believe that, I have a perpetual motion machine I’d like to sell you.

    Sven, thanks for pointing out that the elites don’t rotate much these days. Back in the 90s everyone was talking about the importance of rotation, but that seems to have just been a swim trend that died off.

  6. Canukian says:
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    Don’t really want a deeper pull in backstroke. You want that arm in high at the top and the rotation lets you tuck that elbow into the sweet spot so you can get the hand at the right angle (fingers pointing to the lane rope) ASAP. That is what makes for a longer pull. The top-side speed of the rotation gets that pull started fast and the hip snap rotation releases the water at the end of the pull and the cycle continues.

    If you think about the propulsion phase as what happens when you take your flat palm through a pile of snow (sue me, I live in the great white north!) and that pile builds up the longer you keep your hand in the same position, in a straight line, you can sort of translate it to a backstroke pull. Sort of. But it gives a decent picture/

  7. 1
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    While it is hard to visualize how one creates a force or anchor to pull against using one’s own body, it is true. The rotational motion by itself plays no direct role in propulsion. In fact, the counter-rotation of the body is just one of several energy systems going on while we move down the pool. Another is the recovery of the arm over the water and in shoulder-driven freestyle, the energy of that system also creates a force we can pull against with the opposite hand (not so in hip-driven freestyle, as the arm is already in the water before the other starts the propulsive phase). A third force is generated by the kick and it is not a coincidence that the strongest of the three down kicks that occur during a cycle of a six-beat kicker occurs at the end of the back quadrant propulsive pulling phase, after the counter rotation of the body is completed. I will write more on this later.
    Elite swimmers rotate a lot, but the amount of rotation must be compromised by high stroke rate. The timing is key to make these forces connect.

  8. Clive Rushton says:
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    Interesting, isn’t it? It’s 2014 and we really don’t have much idea how swimmers ‘actually’ swim. There are lots of theories (and Gary’s make great reading and have a lot of substance), but no one actually ‘knows’. Sacrilege, eh?

  9. Mike Lyman says:
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    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 our legs (the reason why, when done correctly, this kick helps lift the legs and put our bodies into a more horizontal position making us more streamlined). The backwards component pushes water behind us thus moving us forward: mass propelled behind equals motion forward.

    Arms are next. The same principle applies; we must push water behind us in order to move forward. A coach when I was younger always liked to say that we were “anchoring our hands” and then just moving past the anchor to swim. While this is an ideal situation, the reality is that our arms don’t stay in exactly one spot as we move forward since water, although dense, is still fluid and will move slightly behind our pull even in the most perfect of strokes. For a moment, let’s got back to high school physics:

    F=ma (force = mass x acceleration)
    The force we are applying is directly proportional to the mass we push behind us (the water behind our arms) and the acceleration of that mass (the increase of speed from the moment we put our hand in the water [0] to the highest speed our arm obtains during our pull).

    THIS is where Gary’s extra force from rotation comes into play.
    Imagine that you are on your side and stationary with no rotation. You then pull your arm down to your side as fast as you can. You have accelerated your arm with an angular momentum caused by the rotation of your arm about your shoulder. The force behind your arm might be represented like this:

    F = [mass of water] x [acceleration of that water (due to your shoulder)].

    Now, let’s say this time you pull with the same acceleration in your shoulder, but you are now rotating your body as well. Your rotating arm is now on a rotating body, which increases the linear speed of your hand through the water. For simplicity’s sake, it’s like throwing a ball 70 mph while standing still compared to throwing it from a car that is moving 10 mph in the same direction. To you on the car, it would seem the ball is moving at 70 mph, but to the bystander on the side of the road who isn’t moving, it would seem that the ball is moving at 80 mph. Our ball has undergone a greater acceleration. Our new force might be represented by this equation:

    F = [mass of water] x [acceleration due to arm + acceleration due to rotation]

    My physics is a bit rusty, but I am certain that the linear speed of your hand through the water with rotation CAN be faster than without rotation.

    Now, I know what your are thinking here. If more rotating creates more acceleration, then wouldn’t it be better to rotate as much as we can? Why not all the way to vertical? Why are we seeing swimmers go faster with a flatter stroke now than what they used to do in the 90’s (when I was an age group swimmer)?

    The answer here is that we are limited to the power of our bodies. The deeper the pull, the more torque we are faced with and thus the more resistance behind our hands. We need more force to generate the same acceleration of the water even though we are pushing more mass (water). There is a limit to how fast we can move our arms and also rotate our bodies. There is obviously a point of diminishing returns, a happy medium where the rotation of our bodies provides some extra hand speed, but doesn’t put our hand so deep or rotate our body so much as to negatively impact the total force that we need to propel water behind us. We also have to take into account the amount of coordination it would take to rotate that much and also whether or not we could effectively kick in those positions. All of these factors are hard to measure exactly in a practical environment.

    Now to address “Because the deeper pull also creates so much more frontal drag force.”
    I have already explained why a super deep pull may not be beneficial as far as moving faster through the water. While this “drag force” idea goes along with the theme that over rotation may not the be the key to swimming faster, I don’t believe that drag force due to hands plays any part in that. The reason is this:

    In the very best possible scenario, we put our arm in the water, anchor it, then move past it as our arm remains in one fixed location in space. Our arm encounters an initial opposing force as we enter the water, but not as we start to pull. In this scenario, our arm faces NO forward drag because we are simply moving past the water that we are pulling, not running into it. In order for our arm to create negative drag against our movement, our bodies would need to be moving faster through the water than our arms (and thus the water would push against them). While this has been proven to be the case with dolphin kick, where individuals have broken world record swim paces by just kicking underwater, it is not the case with free kick especially at the surface of the water, where a kick would be less efficient. Furthermore, as I mentioned earlier, our arm does NOT perfectly anchor and stay stationary in the water but rather it moves backwards towards our feet slightly. Because of this, drag is not an issue.

    Keep in mind that all of the above are merely musings of a former mechanical engineer turned swim coach. If any of you physics majors out there have a more accurate account of what might be happening here (Michael at Rice Aquatics, time to chime in!) I would love to read them.

    Otherwise I think that the take home note here is that Gary Hall Sr. is right about the rotation causing more force for us to pull with, even if it only benefits us up to a certain point.

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