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The Science Behind Wetsuits: How They Reduce Drag and Improve Your Swim Performance
Alexander Caswell-Yee
March 21, 2023
As a triathlete, you know that a wetsuit is an essential piece of gear for open water swims. Not only does it keep you warm, but it also reduces drag, making you faster and more efficient in the water. But how exactly does a wetsuit reduce drag?
Drag is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid (liquid or gas).1 When a solid object (i.e., you) moves through a fluid it will experience a resistive force, called the drag force, opposing its motion. This force is a very complicated force that depends on both the properties of the object and the properties of the fluid. The force depends on the speed, size, and shape of the object. It also depends on the density, viscosity and compressibility of the fluid.2
Long story short, real life drag forces are complicated and hard to exactly measure. However, we don’t need to calculate your exact drag forces to understand how a wetsuit can reduce these forces.
The answer in how a wetsuit does this lies in buoyancy. Buoyancy is the upward force exerted on an object in a fluid, such as water. The wetsuit material construction is designed to provide varying amounts of buoyancy in specific areas to keep you horizonal in the water. This improved body position reduces drag as your plow through the water with your fellow triathletes. A study in 1989 on the effects of wetsuits on drag showed a 12-14% reduction in drag forces when triathletes were wearing a wetsuit compared to when swimming without.3
Credit: Christopher AuYeung
Most high-quality triathlon wetsuits are designed with this buoyancy in mind. They are typically thicker in the lower body, where additional buoyancy is most needed to keep the legs and hips afloat. This buoyancy also helps to improve body position in the water, keeping the hips and legs higher and more streamlined.
The design of the wetsuit can also affect how much drag is reduced. Some wetsuits feature textured surfaces or added panels to break up the water flow and reduce turbulence, which can further reduce drag.
However, this wetsuit effect was tested again in 1989 to compare this effect on triathletes versus competitive swimmers. Chatard et. al. discovered for the triathletes in the experiment, speed and total energy cost of swimming was decreased while wearing a wetsuit. Conversely, for the professional swimmers, the same metrics were not statistically different.4 They concluded the wetsuit effects only reduced drag and improved performance in inefficient swimmers with low buoyancy.
Did they just prove triathletes are just bad swimmers? Also does this mean that wetsuits don’t reduce drag if you have good body position? As with most things, it depends. To understand the full picture, we need to take a step back and look at the whole study and contextualize it with a triathlon wholistically.
Compared to a swimmer whose entire race is physically in the water, a triathlete will typically reduce energy in their kick, to save their legs for the bike and swim portion of the race. The professional swimmers in the study likely maintained a strong kick allowing them to keep a strong horizontal position as they would in a race. Also, the study was done with a 400m swim, which is a short course distance. When extending the swim times into long course races, the additional benefit of buoyancy without expending energy exponentially increases.
So, while wetsuits can certainly help reduce drag and make you faster in the water, it's important to note that they are not a magic bullet. Proper technique and training are still crucial for improving swim performance. In fact, there are many other small technique adjustments you can do to reduce you drag in the water and increase your speed with expending the same amount of energy. More to come!