Kinetic Energy in Swimming – Part 1.2: Wasted Movement Continued

by SwimSwam 11

June 17th, 2014 News, Training

Rebecca Westfall is a former All-American at Texas A&M University, when she was Rebecca Sturdy. She completed her swimming career there in 2007, though still ranks in the top 10 in Texas A&M history in 5 different events. She’s now the assistant coach at Warren Wilson College in Asheville, North Carolina.

Her father, and her coach up until college, is Gary Sturdy. He has a unique perspective on coaching and physics; his primary vocation is as the owner and lead engineer of the Sturdy Engineering Corporation, however he has also spent much of his adult life as a swim coach and swim official. He built a program for the HP-48G that was used at the 2000 Olympic Trials that was used by the USA Swimming Technical Committee to analyze swims.

In Part 1 of our Kinetic Energy in Swimming series, Coach Sturdy and I postulated that physics, more specifically kinetic energy, explains why a reduction in negative kinetic energy results in higher velocities and reduced perceived energy output – “why swimmers go faster when they feel slower.”

Coach Sturdy and I had planned to address the importance of the core in stabilizing workloads in Part 2. However, after reading some of your comments, we have decided that the concept needs to be explained further. Instead, we will build upon the concepts presented in Part 1 and address the need for a new paradigm.

Remember that kinetic energy is defined as mass traveling at a certain velocity and can be expressed in the equation KE=1/2mv2. Positive kinetic energy is the mass of the swimmer traveling in the desired direction in a straight line. Negative kinetic energy is our explanation of wasted kinetic energy, or wasted movement, and is defined as mass traveling in any direction that decreases positive kinetic energy. Lastly KEt = KEp + KEn (For more details, please refer to Part 1 of this series). All of our concepts are based on the work energy theorem detailed in the book Fundamentals of Physics 10th ed.

Actual force balance and drag are not readily measurable, nor observable in swimming, although theories abound. Instead, we aim to focus on kinetic energy and observations of movement. This concept will help pinpoint movements of mass which are detrimental, i.e. negative kinetic energy.

Our focus will be to understand what we observe to be the symptoms of negative kinetic energy. We can then help swimmers adjust accordingly through core and stroke correction, enabling increased positive kinetic energy and, therefore, increased speed.

One common concept of force is that if swimmers increase their force output, then their forward velocity increases. For example, the belief is that if swimmers pull harder or faster on the water, then their speed will increase.

We maintain that it’s not quite as simple as this. Without proper core control (to be addressed in Part 2), swimmers will often unconsciously distort their body alignment to apply more force on the water. A perfect example of this is illustrated when swimmers dig their heads in an effort to pull harder on the water to swim faster. This is especially prevalent in age group swimmers during freestyle sprinting.

This digging head movement creates increased wave action because water is an incompressible liquid and disperses to accommodate the movement of the body. This wave is a symptom of wasted and misdirected movement, which is negative kinetic energy.

Additionally, when the head moves excessively, the whole body usually follows suit in differing directions generating even larger amounts of negative kinetic energy.

If the same swimmers were able to pull harder on the water without losing their body alignment, they would reduce their negative kinetic energy, thereby increasing their positive kinetic energy and forward velocity with less perceived effort.

Obviously correcting the head dig isn’t a new concept. What we want to emphasize is the different mindset that must be applied to kinetic energy in swimming. It’s no longer just a balance of forces and drag. It’s about reducing negative, or wasted, kinetic energies through the analysis of observation of movement. Reduction of negative kinetic energy allows swimmers to propel themselves forward without additional energy expenditures.

Recently, I observed a team of age groupers whom I had never worked with. One of them started to violently throw her head around during a sprint set because she believed she needed to work harder to swim faster. I corrected her and she made the adjustment, but two 50’s later, she reverted to throwing her head. When I asked her why, she replied, “Because it felt slower.”

She did not understand that by reducing the movement of her head, she felt slower because she reduced her negative kinetic energy. She swam faster because she had more positive kinetic energy available. She didn’t believe that she had swum faster until I told her that I had timed her.

Another axiom that is taught to swimmers is that a faster turnover will result in a faster time. The thought process behind this is that the swimmers will be able to take more strokes resulting in increased force on the water and therefore more speed. The backstroke spin drill is an example of this mindset.

While attempting to increase turnover, the swimmers’ core and stroke control often deteriorate because of the additional forces on the water. This inefficient movement increases the negative kinetic energy without a corresponding increase in force. Furthermore, this slippage causes excessive wave action.

So now you have an increase in negative kinetic energy coming from an increased turnover, water movement, AND wave action. Simply slowing the turnover down for the stroke to be more efficient effectively eliminates much of the negative kinetic energy. This automatically corresponds to an increase in positive kinetic energy and therefore an increase in velocity and speed.

You can now understand why Coach Sturdy and I are calling for a change in coaching mind set. No longer should we look for how hard the swimmer is working. Instead we must sharpen our observation skills to analyze how efficiently the swimmer is working. Instead of looking at how much hard work swimmers are putting in, we should train them to channel their efforts to be more efficient and consequently look “slower,” but travel faster.

Returning to my head-throwing age grouper: by reducing her negative kinetic energy, it actually felt to her as if she wasn’t working hard enough. The catch-22 for coaches is that by reducing her negative kinetic energy, it appeared as if she wasn’t working hard enough. But that’s exactly what we want! We maintain that if it looks harder, it probably is!

In conclusion, let’s rewire our eyes and brains to look for swimmers that make it look easy.  Remember the axiom “The greats always make it look easy”? It looks easy because they’ve eliminated much of their negative kinetic energy and are devoting their resources toward accomplishing their goal of increased speed.

In Part 2, we’ll explain how important proper core control and training is to diminish negative kinetic energy.

¹Halliday, David and Robert Resnick. “Fundamentals of Physics”. 10th ed. New York: Wiley, 2014. Print.

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Digging the head reduces the wave energy created by the swimmer. Sun Yang, submarines, and the many studies on barges traveling in rivers and canals agree with me. Lower bow waves = lower negative kinetic energy, therefore digging the head can be very beneficial.


Then why aren’t speedboats made with a bulbous bow? It decreases the bow wave generation, yes, but increases overall drag. The net effect isn’t positive until you have a very large object trying to go through the water (can’t remember exact numbers, but basically we’re talking about a decent sized yacht). Believe it or not, not everything about an aircraft carrier is comparable to a human being.

I remember Dr. Rushall mentioning this at his January USRPT clinic as well, so you aren’t the only one making the comparison. Legit science, bogusly applied.


For ships, the optimal hull shape depends on the Froude number which is the ratio of velocity to surface wave speed. Big ships have a smaller Froude number, small speedboats have a large Froude number. Different flow regimes require different hull designs.


There is no such thing as negative kinetic energy. If you want to understand fluid dynamics you have to solve the Navier-Stokes equation.


I think the author defines negative kinetic energy as any kinetic energy created by the swimmer other than that related to the swimmer’s mass moving through the water. What is wrong with that definition? Why do you say there is no such thing?


My guess is that SwimTroll knows the author is just referring to kinetic energy that has a non-positive effect on swim speed (hence the name) but couldn’t resist bringing up semantics.

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