Swim stroke efficiency: why triathletes get the priority wrong

Most triathletes train the swim the same way they train the bike and run: add volume, build fitness, get faster. It works for the other two disciplines. For swimming, it mostly does not.

Swimming is a technique-first sport. Unlike running or cycling, where fitness is the primary limiter for most athletes, swimming speed is determined first by how cleanly you move through water, and second by how fit you are. Get the order wrong, and more training makes you a fitter version of a slow swimmer.

This is not an opinion. It is a consequence of fluid dynamics, and understanding the mechanism changes how you should structure your swim training, especially if you are an intermediate athlete with limited hours in the water each week.

Why swimming does not respond to volume the way running does

Running and cycling are, at their core, fitness-limited sports. Get fitter, get faster. The movement patterns are intuitive and largely self-correcting. Humans are bipedal. We do not need to learn to run the way we need to learn to swim.

Swimming is a skill-dominant sport. The foundational research from Toussaint and Beek (1992) established that propulsive efficiency, the fraction of muscular energy that actually moves you forward, varies enormously between swimmers and is the primary determinant of speed at sub-elite levels. Their work showed that elite swimmers achieve propulsive efficiency values around 61-70%, while recreational swimmers often sit below 40%. That gap is not a fitness gap. It is a technique gap.

The implication is direct: if you are propulsively inefficient, adding training volume compounds the problem. You are rehearsing a movement pattern that wastes energy, and you are doing it more often.

A 2025 hydrodynamic comparison between competitive swimmers and triathletes confirmed this structural gap. Triathletes showed significantly higher drag profiles than swimmers of comparable aerobic fitness, reflecting years of volume-based training without the technical foundation competitive swimmers build first. The swimmers were faster not because they were fitter, but because they moved through the water more cleanly.

The physics that make technique improvements compound

Water is 800 times denser than air. Drag force in water scales with the square of velocity, which means doubling your speed requires four times the force to overcome resistance. At triathlon paces, this relationship has a practical consequence that most athletes never fully internalise: small improvements in drag profile produce disproportionately large reductions in energy cost.

If you reduce your drag coefficient by 10%, you do not save 10% of your energy expenditure. You save more, because the energy you were spending fighting drag was itself compounding with every increase in pace. The math works in your favour in a way it simply does not in running, where air resistance is negligible at sub-elite speeds.

This is why a technically sound swimmer with modest aerobic capacity will often outpace a fitter athlete with poor form. That fitter athlete is working up to four times harder to overcome drag that the technical swimmer is not generating in the first place, because drag scales with the square of velocity, and every increase in pace multiplies the cost of poor mechanics.

Distance per stroke: the metric most triathletes ignore

Stroke rate is easy to measure and easy to train. Distance per stroke (DPS) is harder to track and harder to improve, which is probably why most triathletes default to the former.

DPS measures how far you travel per arm cycle. It is the direct expression of propulsive efficiency in the water. A swimmer with high DPS is converting each stroke into forward movement. A swimmer with low DPS is churning through the water with effort that dissipates as turbulence rather than translating to speed.

The relationship between stroke length and stroke rate is a genuine trade-off. Increasing stroke rate without maintaining stroke length is the most common error intermediate triathletes make when they feel pressure to swim faster. The result is a higher heart rate, more energy expenditure, and often a similar or slower pace.

The evidence for DPS as a training metric is compelling. A 5% improvement in DPS translates to roughly 18 seconds saved per 100 metres at typical triathlon swim paces. Across a standard 1500m open-water swim, that is over two and a half minutes without any change in fitness. For most age-group athletes, that is a bigger gain than six months of additional swim volume would produce.

The practical test is simple. Count your strokes per 25-metre length. If you are above 20-22 for a relaxed effort, your stroke is leaking propulsion somewhere. Elite open-water swimmers typically hold 16-18 strokes per 25 metres at race effort.

The early vertical forearm catch: what it is and why it matters

The catch phase of freestyle is where most of the propulsive work happens, and it is where most triathletes are losing the most speed.

In a poor catch, the hand enters the water and immediately begins pulling downward and backward. This feels powerful. It is not. A downward pull produces lift, not forward propulsion, and generates significant drag as the body rises and falls in the water.

The early vertical forearm (EVF) catch corrects this. The hand enters the water, the elbow stays high, and the forearm rotates to a vertical position before the pull begins. The result is that a much larger surface area, the entire forearm and hand rather than just the hand, is pressing backward through the water. Forward propulsion increases significantly, and the stroke becomes mechanically efficient rather than just effortful.

The EVF catch is not intuitive. It requires shoulder mobility and proprioceptive awareness that takes deliberate practice to develop. It also requires slowing down to learn it, which is exactly what volume-focused training resists.

Research on hand entry angle and EVF mechanics consistently shows that this single technique element has a larger effect on propulsive force than any other stroke modification available to intermediate swimmers. Getting it right is not a marginal gain. For most triathletes who have never been coached through it, it is a fundamental change in how they move through water.

How to audit your own stroke without a coach

You do not need an underwater camera or a full-time coach to identify the biggest flaws in your stroke. You need a few targeted drills and honest self-assessment.

Count your strokes. As above, 25 metres, relaxed effort, count arm cycles. If you are above 20-22, something is leaking. This tells you there is a problem but not what it is.

The fist drill. Swim 200 metres with your hands closed in fists. This forces your forearm to do the propulsive work your hand was masking. If your pace drops dramatically with fists, your catch is hand-dominant rather than forearm-dominant. This is the most common indicator of a poor EVF.

The catch-up drill. One hand stays extended at the front until the other hand completes its full stroke and returns to the front position. This forces a longer stroke and a pause that reveals whether you are rushing the catch. If the pause feels uncomfortable, you are almost certainly shortening your stroke under fatigue.

Film from the side. If a training partner or a poolside phone can capture even 30 seconds of footage from the side, look for one thing: where is your elbow at the moment your hand begins to pull? If the elbow is dropping below the wrist, the catch is starting too early and the forearm is not engaged. That is the EVF problem, visible in a single frame.

These four checks will identify the highest-leverage issues for most intermediate triathletes without requiring specialist equipment or coaching access.

Open-water swimming changes the technical priorities

Pool technique and open-water technique are not identical, and triathlon-specific technique training should account for the differences.

Sighting. Lifting your head to sight a buoy creates drag and disrupts body position. Most triathletes sight too frequently and too aggressively. The technique is to sight forward during the breathing phase rather than as a separate head-lift, and to reduce sighting frequency by improving navigation confidence. Two to three sights per 100 metres is sufficient in most open-water conditions.

Wetsuit buoyancy. A wetsuit raises your hips and legs, which changes the optimal body position. The low-leg problem that plagues many pool swimmers is largely corrected by wetsuit buoyancy, which means wetsuit swimming rewards a slightly different stroke than pool swimming. Specifically, the kick becomes less important, and athletes can redirect that energy to the upper body pull. Practice in a wetsuit if you race in one.

Drafting. Swimming directly behind another athlete reduces drag by 20-26%, according to research on open-water drafting dynamics. The skill of finding and holding a draft position is worth practising explicitly, but it depends on having a clean enough stroke to maintain position without drifting. Poor technique makes drafting harder to sustain because you cannot hold pace without surging.

A technique-first training block for the off-season

If your next race is more than 12 weeks away, the off-season is the right time to rebuild your stroke from the catch down. Volume is not the goal during this phase. Deliberate practice is.

A practical structure:

• Weeks one to three: Reduce total swim volume by 30-40%. Every session includes at least 400 metres of isolated drill work before any continuous swimming. Focus exclusively on the catch phase. Fist drill, fingertip drag drill, and single-arm freestyle are the primary tools.
• Weeks four to six: Reintroduce continuous swimming, but with a DPS focus. Set a target stroke count per 25 metres (start one stroke below your current average) and hold it. Pace is secondary.
• Weeks seven to ten: Add intensity back in, but monitor stroke count under fatigue. The goal is to hold your improved DPS at higher efforts. If stroke count rises significantly at threshold, you have not yet automated the new pattern. Back off and repeat weeks four to six.
• Weeks eleven to twelve: Return to normal volume with the new mechanics embedded. This is when fitness work becomes productive again.

This is not a permanent reduction in volume. It is a deliberate sequencing that treats technique as the foundation fitness is built on, not as an afterthought.

When volume becomes the right lever

There is a point at which technique is good enough that volume becomes the primary driver of improvement. For most triathletes, that point is further away than they think.

The practical threshold: if your DPS is consistently above 20 strokes per 25 metres, technique is still the primary lever. If you can hold 16-18 strokes at moderate effort and your catch mechanics are sound, adding volume and race-specific intensity will produce meaningful gains.

The swimmers in the Toussaint and Beek (1992) research who were already propulsively efficient responded well to increased training load. The inefficient swimmers did not. Volume rewards efficiency. It does not create it.

The other consideration is the relationship between swim performance and overall race outcome. Research on Olympic-distance triathlon (Millet et al., 2002) found that swim performance had a lower correlation with overall race result than bike or run performance at elite level. This has led some coaches to argue that swim training time is better spent elsewhere.

That argument is worth taking seriously, but it has a specific application. It applies to athletes whose swim is already technically sound and whose limiters are on the bike or run. For athletes with poor swim mechanics, the calculus is different. A technically broken swim costs more energy than a well-executed swim, and that energy cost carries into the bike and run. Fixing the swim is not just about swim time. It is about arriving at T1 with more left.

The interference effect between swim fatigue and subsequent cycling performance is documented in the research (see the interference effect in triathlon training). A more efficient swim means less accumulated fatigue before the bike leg begins. That is a compounding benefit that does not show up in swim split data alone.

What this means for your training

• Swimming is a technique-first sport. Fitness is the second lever, not the first. If your mechanics are poor, more volume will make you a fitter version of a slow swimmer.
• If you are averaging more than 20 strokes per 25-metre length, technique is your primary swim limiter, not fitness. Adding volume before fixing this will entrench the problem.
• Drag scales with velocity squared in water. A 10% reduction in drag profile saves disproportionately more energy at race pace than it would at easy pace, which means technique improvements compound as you get faster.
• The EVF catch is the highest-leverage single technique change available to most intermediate triathletes. Learning it requires slowing down and doing drill work, not adding metres.
• In the off-season, a 10-12 week technique-first block that temporarily reduces volume and prioritises DPS will produce more race-day speed than an equivalent block of fitness-focused volume.
• A more efficient swim reduces accumulated fatigue before the bike and run. The benefit of fixing your stroke is not captured in your swim split alone. It shows up across the entire race.

A platform like Pelaris can track DPS trends alongside training load across all three disciplines, which makes it easier to see whether technique work is translating to efficiency gains before you reintroduce volume.