This is an excerpt from Developing the Core by NSCA -National Strength & Conditioning Association & Jeffrey Willardson.
Fast swimming relies on an athlete's ability to simultaneously generate propulsive force with the arms and legs while attempting to minimize the drag resistance experienced as she knifes through the water. While total-body strength is important, the fastest swimmers are typically those who are able to effectively establish a streamlined body position in the water while also maintaining a base of support from which they can effectively generate propulsion with the arms and legs. Similar to most sports, core muscle conditioning through the torso is critically important to swimming performance.
However, swimming is unique among sports in that the athlete has no interaction with the ground; yet the athlete is still required to maintain a stable torso from which propulsive forces can be generated with the arms and legs. In sports performed on land, ground reaction forces are transferred from the lower extremities through the kinetic chain; this scenario allows a tennis player to generate a high-velocity serve or a football lineman to drive through a block. Conversely, a swimmer not only must effectively engage the core musculature to link the upper body to the lower body but also needs to maintain spinal stability that will establish a base of support from which he can execute proper stroke mechanics.
Poorly conditioned core muscles can lead to technique flaws and inefficiencies that can negatively affect performance and even lead to injury. When it comes to strength and conditioning, the core muscles are arguably the most important area of the body to focus on in swimming, and an effective training program should address all of the muscles that make up the core to achieve muscular balance that enables effective movement in all planes.
Whether it's freestyle, backstroke, butterfly, or breaststroke, every stroke is reliant on well-conditioned core muscles to maintain a stable trunk. This enhances swimming performance in several ways:
- Maintaining a streamlined body position in the water: Whether swimmers are coming off the wall after a turn or swimming on the surface, being streamlined (“punching” as small a hole in the water as possible) reduces drag and makes the propulsive forces that are generated more effective. With poor trunk stability, the legs will likely drop, and excessive energy will be expended to drag them through the water. Additionally, swimmers who have weak core muscles will often fishtail (side-to-side movements of the hips and legs) with every pull and kick, thereby creating extra drag and reducing swimming efficiency even more. Thus, a major advantage of developing trunk stability via well-conditioned core muscles is being able to swim faster without pulling or kicking any harder, simply because drag is reduced with the better body alignment.
- Establishing a stable base of support: It has been said that trunk stability promotes distal limb mobility, and this is definitely the case in swimming. In other words, having good trunk stability allows a swimmer to use the arms and legs for what they were intended—generating propulsion. Many swimmers who lack trunk stability often rely on their arms (e.g., wider or deeper pulls) and legs (e.g., legs splaying apart) to provide balance in the water, especially when breathing. Because of this, the propulsion-generating potential of the arms and legs is not fully realized. Trunk stability provides the base of support needed to generate efficient movement and propulsion with the arms and legs.
- Increasing the effectiveness of the kick: Have you ever tried to push a piece of cooked spaghetti across the dinner table? While pulling it across the table is pretty easy (like pulling the body through the water with your arms), it's very difficult to push it because of the floppiness of the wet spaghetti. This is like trying to use your kick to push yourself across the pool when you have poor core stability. Creating a rigid link between the upper and lower body allows your legs to push you through the water rather than relying entirely on your arms to pull you.
- Generating body roll in freestyle and backstroke: Most swimmers, at one time or another, have been told they need to rotate from the hips when swimming freestyle and backstroke. This body rotation is necessary for efficient pulling and kicking. While some rotation is produced by the kick, much of it comes from the core musculature, particularly the oblique muscles.
- Storing and recovering elastic strain energy: Well-conditioned core muscles allow a swimmer to store energy during certain phases of a stroke that can then be recovered later in the stroke cycle (e.g., storing energy in the core muscles as the torso is raised during the breath in breaststroke and recovering it as the body lunges forward). Having good trunk stability also allows the propulsive forces derived from the kick to drive the body forward, augmenting the power generated by the upper body.
In summary, having a stable trunk enables faster swimming via generation of larger propulsive forces, better streamlining, and more efficient stroke mechanics.
Read more from Developing the Core by the National Strength and Conditioning Association (NSCA) and edited by Jeffrey Willardson.