Swimming Resistance

Swimming resistance is the physical pushing force of water that slows your body down as you move through a pool or the ocean. In sport science, this is called hydrodynamic drag—simply meaning the resistance created by moving through a fluid.

You feel this resistance immediately because freshwater is roughly 800 times denser than air. Every time you take a stroke, your body has to push a heavy wall of water out of the way. How fast or effortlessly you swim comes down to the balance between two opposing forces: propulsion (the forward thrust from your arms and legs) and water resistance pushing back against you.

The Three Factors That Make Moving Through Water Harder

When you swim a lap, total water resistance is made up of three distinct forces acting on your body at the same time:

• Form drag (shape resistance): This is the largest source of resistance for everyday swimmers. As you move forward, water presses tightly against the front of your head and shoulders while leaving a swirling pocket of low-pressure water behind your hips and legs. That pressure gap acts like mild suction pulling you backward. The wider or more angled your body is in the water, the larger this pocket becomes and the more water you have to push aside.

• Wave drag: Swimming at the surface creates ripples and bow waves in front of your head and shoulders. Pushing water upward against gravity to build those waves takes energy away from your forward motion. That is why gliding underwater after pushing off the pool wall feels noticeably faster and smoother than swimming on top of the water—once your body is roughly 0.6 to 0.7 metres below the surface, wave drag almost completely disappears.

• Surface friction: Water clings slightly to your skin, hair and bathers as it slides past. While surface friction plays a much smaller role than your overall body shape, loose boardshorts or baggy swimwear trap pockets of water and noticeably increase drag compared to firm-fitting swimmers.

How Speed, Body Position and Technique Change Resistance

Water resistance does not build up at a gentle, steady rate. Because of the way water behaves, doubling your swimming speed actually quadruples the resistance pushing against your body. When you try to sprint down the lane, the water pushes back far harder than it does during a relaxed swim, which is why trying to "muscle" through the water tires you out so quickly.

Your technique and posture also change the type of drag you experience. When you push off the wall in a tight, flat streamline without kicking, you only face passive drag—the baseline resistance of water flowing past an unchanging shape. As soon as you start stroking and kicking, you create active drag. Moving your arms and legs changes your shape in the water, creating extra swirls and eddies that add resistance even while those movements propel you forward. A smooth, well-timed stroke keeps active drag close to your streamlined passive drag, whereas thrashing or dropping your elbows creates resistance that fights your own effort.

Practical Ways to Reduce Unnecessary Resistance

Because swimming harder multiplies the force of the water pushing against you, streamlining your body alignment is the most effective way to swim further with less effort.

• Keep your eyes looking toward the pool floor: Lifting your head to look forward works like a seesaw—when your head goes up, your hips and legs sink. Sinking legs turn your body into a diagonal snowplough, forcing you to drag your lower body through a deep wall of water. Looking straight down in freestyle keeps your spine flat and your hips riding high near the surface.

• Rotate your shoulders and hips together: In freestyle and backstroke, rolling your torso slightly from side to side with each stroke lets you slice through the water on your narrower edge rather than pushing forward flat on your chest.

• Enter your hands in line with your shoulders: Reaching your lead hand across the centre line of your head throws your body off balance, causing your hips and legs to snake from side to side. That sideways wiggle widens the path your body cuts through the water.

• Keep your kick narrow and compact: Kicking with wide legs or overly bent knees pushes your feet outside the narrow slipstream created by your upper body, catching extra water on every beat.

Swimming Resistance vs Resistance Swimming (Swim Jets)

Although the terms sound nearly identical, swimming resistance and resistance swimming describe two different ways of interacting with water in a backyard pool.

Ordinary swimming resistance happens when the pool water is still and your body travels forward through it. Resistance swimming, on the other hand, means holding your position in one spot while a moving stream of water flows toward you from a swim jet or counter-current unit.

From a purely physical standpoint, water flowing past your skin at 1.2 metres per second feels much the same whether you are swimming forward at 1.2 metres per second in a calm lap pool or holding still against a current moving at that speed. However, the water coming out of a swim jet is already churning and flows fastest right through the middle of the stream, unlike calm pool water. Furthermore, in a still pool, pausing your stroke briefly lets you coast forward until natural drag gradually slows you down. Against a continuous current, the moving water pushes against you non-stop, meaning any drop in your stroke rhythm immediately drifts you backward.

2. Credible Sources:

1. Vennell, R., Pease, D., & Wilson, B. (2006). Wave drag on human swimmers. Journal of Biomechanics, 39(4), 664–671. https://pubmed.ncbi.nlm.nih.gov/16439236/

2. Marinho, D. A., et al. (2011). The Hydrodynamic Study of the Swimming Gliding: a Two-Dimensional Computational Fluid Dynamics (CFD) Analysis. Journal of Human Kinetics, 29, 49–57. https://pmc.ncbi.nlm.nih.gov/articles/PMC3588622/

3. Barbosa, T. M., et al. (2015). A Comparison of Experimental and Analytical Procedures to Measure Passive Drag in Human Swimming. PLOS ONE, 10(7), e0130868. https://pmc.ncbi.nlm.nih.gov/articles/PMC4514895/

4. Lopes, T. J., et al. (2023). A novel method of determining the active drag profile in swimming. Scientific Reports, 13, 10887. https://pmc.ncbi.nlm.nih.gov/articles/PMC10322921/