Where Should Your Next Training Hour Go? The Race Value of Getting Fitter in the Water

Every age-grouper with limited time faces the same question at some point. If I can find one more hour a week, where should it go? For many, the swim is the obvious candidate. It's often the discipline they feel least confident in. It's also the one most often written off: "you can't win a triathlon in the swim, but you can lose it."

This article tries to put some numbers and evidence on that question. It's a companion to TriForward's earlier "Swim Easy, Bike Faster?" article, which looked at how hard to swim on race day. This one asks a different question: what is swim fitness worth across the whole race?

The direct case against: the swim is a small part of finishing time

What large race datasets show

Silva and colleagues (2023) analysed results from 823,459 age-group athletes across 787 Ironman 70.3 races from 2004 to 2020. In correlation analysis, running and cycling were more predictive of overall finishing time than swimming. In their regression analysis, the differences between disciplines weren't statistically significant, so the picture isn't completely one-sided. But the correlations point the same way most coaches would expect.

In professionals, the pattern is clearer. Weiss and colleagues (2024) analysed 16,611 professional Ironman 70.3 records. Bike time correlated with finishing time at about 0.85, run time at about 0.75 for women and 0.82 for men, and swim time at about 0.46 for women and 0.63 for men. Bike time alone explained about 80% of the variation in finishing time, swim time about 41%.

Distance matters too. A 2012 review by Pacheco and colleagues concluded that the swim split correlates with overall result in shorter races, but this relationship doesn't hold for longer distances. That fits with simple proportions. The swim is a bigger share of a sprint than of a full-distance race.

Illustrative arithmetic

Here is a simple calculation, which is TriForward's own illustration, not data from any study. Imagine an age-grouper finishing a 70.3 in about 5 hours 30 minutes, with a 40-minute swim, a 2 hour 50 minute bike and a 1 hour 50 minute run, plus transitions.

• A 5% improvement in the swim saves about 2 minutes.
• A 5% improvement on the bike saves about 8.5 minutes.
• A 5% improvement in the run saves about 5.5 minutes.

On this direct arithmetic alone, the bike wins easily. Even if swim improvements came more easily in percentage terms, they'd need to be much larger to match the minutes available on the bike.

The picture shifts at shorter distances. Take a sprint finisher at about 1 hour 20 minutes, with a 15-minute swim, a 40-minute bike and a 22-minute run, plus transitions. Again, this is illustrative arithmetic. The swim is now nearly a fifth of total time rather than an eighth. A 5% swim gain saves about 45 seconds, against 2 minutes on the bike. The bike still wins on direct minutes, but the gap narrows, which is consistent with the review finding that swim splits matter more in shorter races.

But this is where most analyses stop, and it misses two important effects.

The indirect case for: what the swim costs you

A cheaper swim means a fresher bike

The direct arithmetic treats the swim as an isolated time trial. In reality, how hard the swim is for you affects everything after it.

The clearest evidence comes from Peeling and colleagues (2005). Nine highly trained male triathletes completed lab-based sprint triathlons, swimming 750 m at 80-85%, 90-95% or 98-102% of their swim time-trial speed, then cycling and running at maximal effort. Bike times were faster after the 80-85% and 90-95% swims than after the near-maximal swim, and overall time was faster after the 80-85% swim than after the maximal one.

That study was about pacing, choosing to swim easier. But it shows a principle that applies directly to fitness: the relative intensity of your swim affects your bike.

Delextrat and colleagues (2003) found something similar from a different angle. Eight male triathletes cycled 4.8% more efficiently after a swim done in a drafting position, and the authors linked this to the lower relative intensity of the drafting swim.

Fitness lowers the relative intensity of the same pace

Here's the key link, which is TriForward's inference rather than a direct finding. If you get fitter or more efficient in the water, you can swim the same pace as before at a lower relative intensity. That gives you some of the bike benefit Peeling's athletes got from swimming easier, without losing any swim time. Or you can swim faster at the same relative cost.

The size of this effect hasn't been measured in a fitness-training study. But both mechanisms point the same way, and it means the direct "2 minutes" undervalues swim fitness.

Efficiency matters as much as fitness. Toussaint's 1990 comparison found triathletes turned only about 44% of their stroke power into propulsion, against 62% for competitive swimmers. For inefficient swimmers, technique gains may cut the cost of the swim substantially. It's also where the cost of swimming may be falling most quickly with training. Ambrosini and colleagues (2024) found that eight weeks of kick-focused swim training in 15 triathletes lowered heart rate, oxygen uptake and energy expenditure during cycling straight after swimming.

Who you exit with

Swim fitness also changes the group you come out of the water with. That affects both legal swim drafting, which lowers the cost of the swim, and the competitor effect on the bike, both covered in TriForward's companion article "Out of the Water With the Right Group." Neither effect shows up in a simple split-time calculation.

Why "you can't win it in the swim" is half right

The old saying captures the direct arithmetic well. In most age-group races, especially long ones, the minutes available in the swim are fewer than on the bike or run, and the race-data correlations agree. Nobody should expect a better swim alone to turn a mid-pack finish into a podium.

The second half, "but you can lose it," is where the indirect effects sit. A swim that leaves you over-fatigued, isolated from athletes of your level, or rattled by a stressful start can cost more on the bike and run than the swim split itself shows. None of that appears in a split-time spreadsheet, and none of it has been precisely measured in age-groupers. But each piece has some support. Lower relative swim intensity helped the bike in lab studies. Drafting made the following ride more efficient. Racing alongside competitors changed how cyclists paced and performed.

A more accurate version of the saying might be this: you rarely win a triathlon in the swim, but a weak swim makes the rest of your race more expensive. Whether fixing that is worth an extra hour depends on how weak your swim is and how much it's costing you downstream.

The age factor

There's one more reason not to neglect swimming, especially for older athletes. Käch and colleagues (2018) analysed more than 410,000 Ironman results (329,066 men and 81,815 women, 2002-2015). Age-related performance decline started earlier in swimming than in cycling or running, from around age 25-29 in both sexes. In cycling and running, decline began at 30-34 for women and 35-39 for men.

These are cross-sectional race results, not individuals tracked over time. But they suggest that swim performance is the first to slip with age. Maintaining swim fitness may become relatively more valuable as you get older, if only to hold your position. That's an inference.

So where should your next hour go?

There's no universal answer, but there is a sensible way to decide. The following framework is TriForward's synthesis, not a tested model.

Signals that the extra hour belongs in the pool

• Your swim is weak relative to the rest of your race. Compare your split rankings within your age group. If you're mid-pack on the bike and run but near the back in the swim, the swim is your relative weakness, and you may be exiting with a slower group than your bike deserves.
• You race sprint or Olympic distance. The swim is a larger share of total time, and the review evidence suggests swim splits matter more for results at shorter distances.
• Your swim is inefficient. If your stroke count is high and you can't go much faster even fresh, technique gains may come quickly and cut the cost of the swim. See "Six Months, Same Pace."
• You finish the swim already tired. If you start the bike breathing hard and need a long time to settle, a less costly swim is likely to help your bike.
• You're in an older age group. Swim decline starts earliest, so maintaining or improving swim fitness may protect your overall result.
• You're anxious in open water. Swim fitness and confidence also make you safer and calmer at the start, which has its own value.

Signals that the hour belongs elsewhere

• Your swim is already strong relative to your bike and run, and you're exiting with groups you can't match on the bike.
• You race half or full distance and your bike is your weakest leg. The direct time available on the bike is usually larger.
• You're limited by bike durability or run fade. If your power drops sharply late in the bike, or your run falls apart, that's where the biggest gains lie. See TriForward's bike durability articles, such as "Why Watts Fade" and "Fresh Watts vs. Hour-Four Watts".
• You already swim three or more times a week with structure, and further gains will come slowly.

Running the numbers for your own race

You can apply this framework to your own results in a few minutes. It's a rough tool, not a validated method.

1. Find your age-group rankings for each split in a recent race. Most results services show split positions. Convert each to a rough percentile: 30th of 100 is the top 30%.
2. Look for the outlier. If one discipline ranks far below the other two, that's your relative weakness. A large gap matters more than a small one.
3. Work out the direct minutes available. Multiply each split by a realistic improvement, say 3-5% over a season. This shows the direct time at stake in each discipline.
4. Adjust for knock-on effects. If your swim is your weakness and you start the bike tired, give the swim some extra credit beyond its direct minutes. The research can't tell you how much, so this is judgement.
5. Factor in time cost. An hour in the pool often costs more than an hour of life once travel and changing are added. An indoor bike session may cost exactly an hour. If pool time is expensive for you, the efficiency of each session matters even more.

Consider the injury picture too

The discipline you can train most consistently matters. Swimming is low-impact, so for athletes prone to running injuries, extra swim time may add aerobic training without adding impact load. That's a reasonable judgement rather than a tested finding. Swimming isn't free of risk, though. Shoulder pain is common when swim volume rises quickly, as covered in "Swimmer's Shoulder in Triathletes." If you add swim time, build it gradually.

The practical middle ground

For many age-groupers, the right answer isn't more swim volume. It's better use of existing swim time. Adding structure, technique feedback and a critical swim speed test to the sessions you already do may deliver the efficiency and fitness benefits without taking an hour from the bike or run. See "The 45-Minute Pool Session" and "Critical Swim Speed."

A note on what the evidence can and can't tell you

The race-data analyses describe correlations across large groups. They show which split tracks finishing time most closely, not what would happen if you, specifically, improved one discipline. The lab studies linking swim intensity to bike performance used small groups of trained male triathletes in sprint-distance lab protocols. The time arithmetic in this article is illustrative. Nobody has run a study assigning age-groupers an extra hour in the pool versus on the bike and comparing race results.

What the evidence does support is that the swim matters more than its share of finishing time suggests, because of what it costs you for the rest of the race. How much more depends on your relative strengths, your race distance and your age.

References

• Silva C, Nikolaidis PT, Valero D, Weiss K, Villiger E, Thuany M, Andrade M, Knechtle B. Predicting overall performance in Ironman 70.3 age group triathletes through split disciplines. Scientific Reports, 2023;13:11492. Loyola Marymount University repository record
• Weiss K, Valero D, Andrade MS, Villiger E, Thuany M, Knechtle B. Cycling is the most important predictive split discipline in professional Ironman 70.3 triathletes. Frontiers in Sports and Active Living, 2024. doi:10.3389/fspor.2024.1214929
• Pacheco AG, Leite GS, de Lucas RD, Guglielmo LGA. The influence of swimming performance in triathlon: implications for training and competition. Revista Brasileira de Cineantropometria e Desempenho Humano, 2012;14(2):232. doi:10.5007/1980-0037.2012v14n2p232
• Peeling P, Bishop D, Landers GJ. Effect of swimming intensity on subsequent cycling and overall triathlon performance. British Journal of Sports Medicine, 2005;39(12):960–964. doi:10.1136/bjsm.2005.020370
• Delextrat A, Tricot V, Bernard T, Vercruyssen F, Hausswirth C, Brisswalter J. Drafting during swimming improves efficiency during subsequent cycling. Medicine & Science in Sports & Exercise, 2003. doi:10.1249/01.MSS.0000084422.49491.2C
• Toussaint HM. Differences in propelling efficiency between competitive and triathlon swimmers. Medicine & Science in Sports & Exercise, 1990;22(3):409–415. PubMed 2381311
• Ambrosini L, Presta V, Vitale M, Menegatti E, Guarnieri A, Bianchi V, De Munari I, Condello G, Gobbi G. A higher kick frequency swimming training program optimizes swim-to-cycle transition in triathlon. Journal of Strength and Conditioning Research, 2024. doi:10.1519/JSC.0000000000004731
• Käch IW, Rüst CA, Nikolaidis PT, Rosemann T, Knechtle B. The age-related performance decline in Ironman triathlon starts earlier in swimming than in cycling and running. Journal of Strength and Conditioning Research, 2018;32(2):379–395. doi:10.1519/JSC.0000000000001796