Kinetic Energy in Swimming – Part 2: The Core is King

by SwimSwam 4

September 14th, 2014 News, Training, Training Intel

Since we last caught up with Rebecca Westfall and Gary Sturdy’s exploration of swimming and physics, Rebecca’s has found a new job – as the assistant coach at UNC-Asheville. That new role has only furthered her passion for unlocking the magi formula to swimming fast through exploration of kinetic energy. See more below.

By: Rebecca (Sturdy) Westfall and Gary Sturdy, P.E.

In part one of our Kinetic Energy in Swimming series, Coach Gary Sturdy and I proposed applying physics to swimming, more specifically the concept of kinetic energy.

We used the example of the zig-zag and digging of the head, in previous articles, to illustrate our point. We described the problems behind the movement, but didn’t tell you HOW to fix the problem. Our solution comes from applying physics to “engineering the foundation of the stroke,” i.e. the “core.”

When engineering a building, one must first analyze its various loading conditions. These loading conditions can produce the greatest stress on the individual members and the structure as a whole. Frequently, the loads are paired together such as a snow loaded roof during a wind storm. All these loads are initially placed onto one or more small groups of members (studs, joists, beans, rafters, etc.) at the outermost extremities of the structure. These loads are transferred into an ever increasing number of support members (walls, floors, roof, etc.) until all the loads reach the foundation.

The foundation holds all the members in place, accepting loads without wavering, allowing all the supportive members to remain stable and strong. The integrity of the structure demands a stable and strong foundation. A strong foundation holds all the members in place, accepting loads without wavering, allowing the members extending from the foundation out to the extremities to remain stable and stationary. Without a strong foundation, buildings lean, lose integrity and eventually fail.

The strength of the typical foundation is gained through the use of multiple materials. A typical foundation is constructed of concrete and reinforcing steel (rebar). These two materials, when loaded separately, may withstand certain loads, but not all loads. For example, concrete is excellent in compression, but fails in tension. Rebar is excellent in tension, but fails in compression. Concrete and rebar working in tandem enable skyscrapers to stand tall and for great lengths of time.

As the foundation is vital to the structural integrity of a building, so is the core to the structural integrity of the stroke. Without a stable, strong core, a host of problems present themselves. Using our engineering analogy, observation and analysis of body movement and the surrounding water allows us to see problems with conventional core training.

The word “core” has been a popular catch-word in sports for several years. In our paradigm of coaching, the core includes an obscure deep abdominal muscle group call the iliopsoas and the quadratus luborum (QL). The QL has always been considered a back muscle, but it is actually the deepest muscle of the abdomen. Because of where they attach, these muscles contribute to core stability.

Our definition of core muscles also includes the commonly referenced muscles of the abdomen from deep to superficial: the transverse abdominis (TA), inner obliques, external obliques and rectus abdominis. All these muscles work collectively to stabilize the trunk and provide added strength and efficiency to appendicular body parts and limbs. These muscles can also be visualized as a corset.

Referring back to our previous engineering example, the transverse abdominis serves the same function as rebar in the foundation of the building. When the TA is activated, the already strong core becomes more stable and anchored.

In our observations, the transverse abdominis is the core muscle most difficult to train and control because it is the deepest. Its primary function is compression of the abdominal contents, but in swimming, it is also balance and stability related. During everyday activities, it is used synergistically and almost unconsciously with the other core muscles and hip complexes. As the TA is not a primary mover, it is almost impossible to completely isolate it. Because of this difficulty, we use verbal and visual cues to help the swimmer learn to employ the TA.

First, activate the pelvic floor muscles by instructing the swimmer to cease an imaginary flow of urine. While contracting the pelvic floor, the swimmer should then attempt to contract the deepest parts of their abdominal wall by pulling their lower abdominals in and upwards towards the belly button. By contracting the pelvic floor, most swimmers are able to feel increased sensitivity in their lower abdominals and given enough practice, they can more clearly distinguish the different layers of musculature.

The ability to effectively utilize the TA is of great importance. In this paradigm, we must teach the core to respond to the specific stresses of the stroke. However, core training must be used properly. For example, we believe that crunches and sit-ups do not address TA training and can actually be detrimental. Excessive use of these conventional exercise actually shorten the rectus abdominis (“abs”), which results in a forward posture of the chin and hips.

However, this short, tight and limiting posture is not conducive to swimming. It affects the ability of the swimmer’s body to remain long and in optimal alignment, while also affecting the stroke by limiting the range of motion of the shoulders. We advocate long, smooth muscles throughout the entire body which, in turn, implicates a different standard of weight training methods.

To expand upon the importance of core training, we observe that many swimmers use their hands, arms, legs and feet to balance themselves in the water rather than utilizing the core. For example, swimmers balance themselves with their hands and arms in order to raise their head to breathe. The zig-zag is also a symptom of appendicular balance.

Not only can these movements eventually cause shoulder and spine problems, but it is also negative kinetic energy, i.e. wasted kinetic energy. More negative kinetic energy as a result of this wasted movement is observed in movement of the water away from body parts, or excessive wave action.

Transferring this balancing movement of the extremities to the core not only decreases negative kinetic energy, but it also increases the strength of the entire body structure. Using the core as a solid foundation, the extremities are able to become more efficient and strong. In certain, specific instances, primary emphasis on the core will sometimes cause a natural correction of stroke flaws.

Demonstrating our concepts of core training, the following are three drills which increase the core’s awareness and sensitivity:

1. Swimmer A closes his eyes and stands with two feet firmly grounded and stabilizes his body using his core. When the core is properly stabilized, he should not be able to “belly breathe.” Instead he should focus on breathing into the deepest part of the lungs, allowing the rib cage to expand to the sides while keeping the shoulders down. (It is important to note that this method of breathing should be employed in the pool as well.)

When Swimmer A is prepared, Swimmer B pushes the hips of Swimmer A in different directions forcing Swimmer A to correct and balance. Swimmer A should attempt to not allow any movement in the core. Shearing, twisting, breaking, and movement of the ribs are symptoms of core instability. Swimmer B provides verbal and physical feedback by pointing out any extraneous movement while Swimmer A attempts to make corrections. The two swimmers then switch roles and the process begins again.

2. Once both swimmers have mastered this exercise, both swimmers stand face-to-face with hands at chest level. Swimmer B then manipulates Swimmer A’s hands by pushing one or both hands in any direction. Swimmer A must allow the arm movement, but attempt to keep the core as a solid, unmoving foundation.

Progressing in the same face-to-face position, each swimmer mimics the arm movements of the stroke without allowing the core to break. The goal is for the swimmers to be able to allow movement of any appendage without movement in the core. Using one hand helps isolate individual movements, while dual handed movements require increased stability under combined loading conditions.

3. The third exercise tests the strength of the connectivity of the hips and shoulders during the body roll. This exercise also works best in pairs. Swimmer A lies on his side in a streamline position with arms extended over the head and all body parts correctly aligned. Again, attention should be paid to proper breathing techniques.

Swimmer A then attempts to roll his shoulders and hips in unison to the floor and from the floor back up to his side in a slow, controlled movement without breaking the core foundation or body alignment, i.e. no twisting, or shearing. The whole body should move as a single unit. (Caution: swimmers are apt to hold their breath and tense their chest and shoulders to accomplish this movement.)

Swimmer B can aid this process by holding the shoulder and hip while helping Swimmer A to control the movement. Swimmer B also provides feedback on any extraneous movement. Again, the two swimmers switch roles.

While conventional abdominal exercises can be used to help strengthen the core, they must be performed correctly within the system. Too often, these conventional “abs” are performed with the swimmer bearing out and down on their rectus abdominis and external obliques. The swimmer must pull the transverse abdominis in towards the spine and up towards the belly button. The belly should remain flat and compact during all movements.

Symptoms of poor transverse abdominis control include the “bread loaf,” where the rectus abdominis is raised from the rest of the abdominal wall, and the “pot belly,” in which the entire abdominal wall pushes away from the spine creating a distended look.

These three drills and other abdominal exercises can teach swimmers how to actively control the external forces directed at their core while on land. Once the swimmers move to the water, they will have an increased knowledge of how the movement of their arms and legs affects the stability of their foundation.

Swimmers should intensely monitor the movement and function of their core not once daily but with every stroke taken. The core foundation becomes “King” and is the most important part of the stroke.

In Part Three, we will pinpoint specific sources of kinetic energy in freestyle and then discuss ways to reduce negative kinetic energy and increase positive kinetic energy. Can we study how oar catch-and-release affects hull movement in the sport of rowing and apply it to swimming?

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I need some clarification. “When the core is properly stabilized, he should not be able to “belly breathe.” Instead he should focus on breathing into the deepest part of the lungs, allowing the rib cage to expand to the sides while keeping the shoulders down. (It is important to note that this method of breathing should be employed in the pool as well.)” I’m a bit hung up on belly breathing. This article says not to do it when swimming, yet my understanding is that belly breathing properly engages the diaphragm and allows air to access all parts of the lungs, providing more oxygen. So you shouldn’t be able to belly breathe, but you should be able to get air… Read more »


That’s a good question Sven. I’ll try and pull it together for you. The first thing to think about is that our transverse abdominis is like a corset wrapping between our pelvis and rib cage. So when it is contracted there shouldn’t be any outward movement of the stomach, this doesn’t mean u aren’t using the diaphragm. The core should be thought of as a barrel with the pelvic floor being the bottom, the trans abd being the sides and the diaphragm being the top. The diaphragms job is to pull air down into the lungs which sit on top of that barrel. This creates pressure on our barrel. If the core isn’t tight then the side of the barrel… Read more »

The abdominal contents between the diaphragm and pelvic floor are for the most part, non-compressible, aside from the air in the gut. Diaphragmatic breathing creates increased intraabdominal pressure which will cause some excursion of the abdomen outward. However the TA can still be toned and control the posture while also allowing movement. Otherwise I do agree that air intake is compromised and breathing shallower. Perhaps the idea of “IAP” increased abdominal pressure as a key feature of proper core activation would be easier…there will be a pressure sensation when the abdominal muscles are properly held in good tone with breathing.

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