Why The Fundamental Law of Inertia Matters In Swimming

Courtesy of Gary Hall Sr., 10-time World Record Holder, 3-time Olympian, 1976 Olympic Games US Flagbearer and The Race Club co-founder.

At The Race Club, inertia is the third fundamental law we teach our swimmers. Although Newton is often credited for this law (his first law of motion), it was actually Galileo that was the first to conceptualize inertia.

A Moving Body Resists Changing Its Speed

The definition of inertia is a body in motion tends to want to stay in motion. In other words, a moving body resists changing its speed. The same holds true for a car on the freeway as it does for a body swimming down the pool. The frontal drag forces are working to slow us down whenever we are moving, so to maintain a more constant speed requires that we maintain a near-constant propulsion. Although this takes work, it actually requires a lot less work than if we were to stop or slow down appreciably and try to regain the original speed. A good example is when you completely misjudge the wall on a flip turn, pushing against nothing but water. The result is a total loss of speed and the effort to get back to race speed from this dead stop is overwhelming.

The Freeway Strokes

There are really only two inertia strokes; freestyle and backstroke. I call them the freeway strokes. Because of the way in which we generate propulsion in fly and breast, abrupt changes in body speed are unavoidable. Consequently, these two stop-and-go strokes are both difficult and inefficient. Yet, even in those strokes, the law of inertia still applies.

There are only three things I can think of one can do to comply with this law of inertia in freestyle and backstroke, in order to keep the body speed more constant. The first is to kick with a six-beat kick, trying to generate some propulsive force on both the down and the up kick.

The second is to increase the pulling stroke rate (decrease the cycle time). For a freestyle sprinter with a stroke rate of 120 strokes per minute (60 right arms and 60 left arms), the cycle time is one second. The propulsive phase (when the hand is actually moving backward) in front and back quadrants is about .35 seconds. For both hands that means that .7 seconds of the one-second cycle time (70%) is spent actually propelling the body forward. The rest of the time the hand is either lifting the body or recovering. Either way, it is in propulsive ‘down time’. The faster the stroke rate, the less propulsive ‘down time’ and the more constant the speed.

Distance Swimmers Must Have a Strong 6-Beat Kick

For distance swimmers, like Sun Yang, who use a stroke rate in the middle of the 1500 of 60 (cycle time 2 seconds), the time in propulsive phase is still .7 seconds, but that represents only 35% of the total cycle time. That does not bode well for the law of inertia. For this reason, hip-driven (slow stroke rate) freestylers must have strong six-beat kicks to obey this law.

Reduce Frontal Drag

Finally, the third way to abide by this fundamental law of maintaining constant speed is to reduce frontal drag as much as possible. This is accomplished by keeping the head in alignment with the body and getting the head underwater at the crucial time of hand entry, keeping the body and legs in as straight a line as possible and by pulling under water with a high elbow position. In testing myself with the velocity meter using arms-only freestyle, with a deep pull, the body speed dropped by nearly 40% from hand entry to the initiation of the propulsive phase (.3 seconds in a sprint). With the high elbow pull, the body speed dropped by 30% during the same phase. While that may not seem like a huge difference, when it comes to inertia, every bit helps.

George Bovell demonstrates some creative drills for fast swimming: http://www.theraceclub.com/videos/swimming-technique-videos/ 

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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Swim Training / Swimming News courtesy of The Race Club / Gary Hall Sr.

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Bossanova

So he’s saying Sun Yang would be faster with a 6 beat kick?

Colin

I believe he is. Would a 6-beat kick be sustainable for Sun Yang? I believe Sun Yang has found what works best for him.

Sven

Yep. And he’s not wrong. It’s a bold statement, but Sun Yang could be faster. Would it jive with the way he swims the mile? I don’t know. He probably wouldn’t be able to finish as insanely fast, so his strategy would probably have to change. So that’s the thing, Sun Yang and his coach apparently haven’t found a way to apply that change such that it improves his performance, but the potential is definitely there. And if nothing else, it could just be another case like Janet Evans: no one really knew why her stroke was so different from her peers, and none of them could replicate it with the same results, she was just an anomaly.

ML

From what I’ve seen Sun Yang already uses a 6 beat kick quite often, including during parts of every lap of the mile. It’s often light, but it’s there. Sometimes he goes to 4 beats mid-lap.

SprintDude9000

There’s absolutely no way Sun Yang would be faster with a 6 beat kick for a number of reasons: 1. Kicking whilst travelling through water above a certain speed increases form drag a massive amount (since form drag increases as the square of velocity). Kicking more often and/or kicking harder will do nothing but increase drag and slow a swimmer down. (Sun Yang and his coaches most likely know this and have minimized his kick accordingly.) There’s a good Total Immersion article about the subject here: http://archive.totalimmersion.net/sme-excerpt-kick.html 2. Kicking whilst swimming full-stroke is (in itself) virtually non-propulsive. This is because the direction of water displacement depends on the type of kick being undertaken. For example, whilst kicking with a kickboard,… Read more »

I disagree with some of what you are saying. Sun Yang is a lot faster with a full out six-beat kick and demonstrates that in the final 100 meters of his 1500. On the last lap, his stroke rate also goes from 60 to 90 per minute, which also makes a huge difference. With regard to 1., form or pressure drag is exponentially related to speed (velocity squared), so increasing the speed does substantially increase this drag (this is why technique becomes of greater importance at higher speed). The propulsive force of the legs is driven by the speed and surface area of the foot and the distance that foot can travelat hight speed. During the flick of the ankle,… Read more »

sprintdude9000

From a purely propulsive perspective I interpret Sun Yang’s increased finishing speed to be solely due to his increased stroke rate (which you say yourself makes a huge difference). This increase in arm acceleration produces bigger vertical forces which require bigger counterbalancing kicks (in order to allow Yang to maintain his body position). Visually this may give the impression that Yang’s harder kicks are providing him with more propulsion but scientific evidence suggests that this is not the case. (That said, these larger [counterbalancing] kicks might be required nonetheless in order to keep his body flat and indeed he may not be as fast without them. If he were to kick as hard as this prior to increasing his stroke… Read more »

Ben

the sport of swimming is all about maximizing average velocity while obeying certain constraints. Everything in the article is “true” in a sense because kicking harder or increasing stroke tempo etc, etc… will definitely increase velocity. The issue is that this disregards the constraints. Case in point: Sun Yang 1500 Sun Yang could definitely do any single part of his race faster by either kicking harder or increasing his stroke rate or some combination of both. I’m nearly certain that by the 1000 meter mark his heart rate is at or above ~185. If he were to start kicking harder then he would certainly go faster but it might push him past that point of no return. If he goes… Read more »

SprintDude9000

“Everything in the article is “true” in a sense because kicking harder or increasing stroke tempo etc, etc… will definitely increase velocity.” No – kicking harder will not increase full stroke swimming velocity. From the Total Immersion article about the Doc Councilman experiment that I linked above: “at any speed over 5 feet per second (1:00 per 100 yards) the kick contributed nothing and, in some instances, actually increased drag! Counsilman interpreted these results using an automotive metaphor. Imagine, he suggested, a car with separate front- and rear-wheel drive. If the front wheels turn at 30 mph, but the rear wheels turn at 20 mph, the car’s total speed will be not 50 but less than 30 mph, because the… Read more »

Sven

I’m not saying he needs to have a full out Thorpe kick for the whole 1500, but that the 6 beat kick balances out the stroke better and helps smooth out some of the dead spots in the stroke. Yeah, having a huge, splashy kick for a mile would be inefficient, but don’t make the mistake of automatically equating “6 beat” with “sprint.” A relaxed, consistent six beat kick is easily maintainable and it facilitates an even tempo and quick breathing. When you say he should stop doing catch up, do you mean he should work toward a shoulder driven opposition stroke, like Dr. Rushall advocates for all distances? If so, I’d have to disagree. If efficiency is a concern,… Read more »

SprintDude9000

“When you say he should stop doing catch up, do you mean he should work toward a shoulder driven opposition stroke, like Dr. Rushall advocates for all distances?” Not necessarily, I just mean that he should stop swimming with a catch-up in order to address the law of inertia Gary wrote this article about. “If efficiency is a concern, then a hip-driven stroke is the only option.” In theory a hip-driven 3/4 catch up is actually less efficient than an evenly timed opposition stroke due to the dead spots you mention. “That’s why the kick is so important: the overlapping of strokes causes dead spots in propulsion, and a consistent kick helps to minimize those (whether through direct propulsion or… Read more »

Sven

Thorpe’s kick is gigantic, I’m not advocating for that. As I said, a small, relaxed 6 beat won’t be so far outside the bodyline that it slows the swimmer, while still balancing out the stroke.

Re: catch-up: If, in theory, removing the catch-up aspect would be more efficient (i.e. the same/better speed for less/the same fatigue), then the theory is flawed. The concept isn’t secret, many coaches have tried it out, it just isn’t sustainable over certain distances for everyone whose name doesn’t rhyme with Planet Sevens.

SprintDude9000

“Thorpe’s kick is gigantic, I’m not advocating for that. As I said, a small, relaxed 6 beat won’t be so far outside the bodyline that it slows the swimmer, while still balancing out the stroke.” I think we are on the same page in regard to kick magnitude then. “Re: catch-up: If, in theory, removing the catch-up aspect would be more efficient (i.e. the same/better speed for less/the same fatigue), then the theory is flawed.” The theory in question is in fact the law of inertia that Gary is talking about in the article. “The concept isn’t secret, many coaches have tried it out” I am a coach who has tried it out and have had my swimmers improve as… Read more »

Monroe

I don’t believe I’ve ever heard anyone apply total immersion to competitive swimming before.

I thought it was all S-strokes and over rotating side to side compared to swimmers with high elbow catches and 25-35 degree rotations where one rotates forward.

http://usaswimming.org/ViewNewsArticle.aspx?TabId=2175&itemid=4101&mid=11657

Also, If someone is slower from kicking more in their freestyle they are either really bad at kicking or they simply haven’t mastered the connection yet.

SprintDude9000

“I don’t believe I’ve ever heard anyone apply total immersion to competitive swimming before” Total Immersion have so much right in regards to streamlining, kick and efficiency which translates very nicely to competitive swimming – keep an open mind. Anyway that’s largely irrelevant since the article I posted is about Doc Councilman’s findings in competitive swimming at Indiana University. “If someone is slower from kicking more in their freestyle they are either really bad at kicking or they simply haven’t mastered the connection yet.” People benefit from kicking for balance but not by kicking ‘more’ or ‘harder’ in order to try and increase propulsion (which is what I assume you are talking about). The Total Immersion article and various scientific… Read more »

asdf

I love that science, physics, and that the process of experimentation is being utilized in coaching today, but I believe the laws of physics are not properly understood by all people trying to do this. For example ” Kicking whilst travelling through water above a certain speed increases form drag a massive amount (since form drag increases as the square of velocity). Kicking more often and/or kicking harder will do nothing but increase drag and slow a swimmer down. (Sun Yang and his coaches most likely know this and have minimized his kick accordingly.) ” This relationship is a fact. There will be greater drag as the swimmer displaces more water. However if the swimmers are able to maintain there… Read more »

Sven

SprintDude: Reading this, I realized that you and I were using different meanings when we use the word “efficient.” Efficiency in the context of one stroke cycle is totally different from efficiency in the context of an entire race. I was using it in the latter context, because, to me, final time is what matters. Just like the grip strength example given above, those dead spots in the stroke are necessary to sustain overall performance, and kicking helps to minimize the negative effects of said dead spots. Hopefully it makes more sense when put in that light.

Two comments: 1. Don’t confuse the motion of the legs with the motion and direction of the flick of the foot/ankle. They are very different. The propulsion comes from the foot, not the legs. In order to move the body forward in the water, there has to be a force applied in the rearward direction. Both the hands and feet (of fast swimmers) do that. 2. While efficiency is important in swimming, it alone does not win races. No one gives away medals in a car race for having the best gas mileage, nor do they in a swimming race for burning the fewest calories per meter swum. Especially in sprints, one has to push the pedal to the metal… Read more »

SprintDude9000

Sven – to be honest it’s probably my fault for not being clearer!

Three comments: 1. Don’t confuse the motion of the legs with the motion and direction of the flick of the foot/ankle. They are very different. The propulsion comes from the feet, not the legs. In order to move the body forward in the water, there has to be a force applied in the rearward direction. Both the hands and feet (of fast swimmers) do that. 2. While efficiency is important in swimming, it alone does not win races. No one gives away medals in a car race for having the best gas mileage, nor do they in a swimming race for burning the fewest calories per meter swum. Especially in sprints, one has to push the pedal to the metal… Read more »

asdf

I don’t know if these were points trying to refute something I said or if they were additional points Gary. But I agree with the first two and I don’t believe they contradict anything I have said. If they do please let me know so that I can address how I believe they actually work into what I have written. As for the 3rd point I take back the statement that catchup is the only way to swim. I should know better than to talk in absolutes. I was not trying to imply that one could not use different styles of freestyle in the 1500. I was just trying to show why a hip driven freestyle or Hybrid freestyle is… Read more »

SprintDude9000

Wow, this is developing into a great discussion…love it! In reply to ASDF: “The way that you have presented this relationship in physics it sounds like you believe swimmers shouldn’t kick off of a start or turn either since that is when they are going the fastest and kicking would only result in there speed being lost faster. It is obvious that kicking off the start and turn is beneficial in swimming as all great swimmers do it.” It shouldn’t have since I addressed what you’ve just written in my first comment whilst describing the differences in the overall direction of water displacement between kickboard kicking and full-stroke swim kicking. Isolated kick is indeed more propulsive than full stroke kicking… Read more »

ML

To see how rest time could differ between a catch-up stroke and a non-catch-up stroke with the same stroke rate, just think: in order to match the stroke rate of a non-catch-up swimmer, a catch-up swimmer will have to make up for any amount of time spent with one arm stationary, by speeding up his pull or his over-the-water recovery or both. This suggests that a catch-up stroke can offer increased rest time in exchange for a more intense pull. Is that tradeoff sometimes worthwhile? If dead spots are the concern, it seems more helpful to focus not on time spent with one arm stationary, but rather on time spent with neither arm pulling (i.e., time spent gliding). The longer… Read more »

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