Six Months, Same Pace: Why Age-Group Swimmers Plateau and What Actually Moves the Needle

It's one of the most common and demoralising experiences in age-group triathlon. You commit to the pool, two or three times a week, for months. You get fitter, and sessions feel easier, but the clock barely moves. Your 100 m pace in month six looks almost the same as in month one.

That isn't a sign you're "not a swimmer." It's usually a sign that the training is aimed at the wrong limiter. This article looks at the evidence on why triathletes stall in the water, what changes tend to move pace, and how to tell which of the usual causes applies to you. It sits alongside TriForward's earlier article "Stroke Rate vs. Distance-Per-Stroke," which covers stroke mechanics in more depth.

The efficiency gap: why fitness alone stalls

The most striking piece of evidence here is old and small, but it's a useful starting point. In 1990, Huub Toussaint compared six competitive swimmers with five triathletes, working at the same power output. Both groups had similar gross efficiency, meaning they turned metabolic energy into mechanical work about equally well. The difference was in what happened to that work.

Toussaint measured propelling efficiency: the share of total power that actually goes into overcoming drag and moving you forward, rather than being lost pushing water around. Competitive swimmers reached 62% (±6%). Triathletes managed 44% (±4%). At the same power, the swimmers covered 1.28 m per stroke and swam at 1.11 m/s. The triathletes covered 0.99 m per stroke at 0.90 m/s.

Caveats first. That's eleven people, measured more than three decades ago, and their sex isn't reported in the abstract we reviewed. It shouldn't be read as a precise number for today's age-groupers. But the mechanism it points to is well supported in swimming biomechanics and makes intuitive sense. In water, a large share of the energy you produce can be spent moving water rather than moving you. Swimming isn't like cycling, where extra fitness flows to the pedals fairly directly.

The practical consequence is what matters. If more than half of your effort is lost to inefficient propulsion, aerobic gains get diluted. You can raise your engine's output and still see little change in speed, because the transmission is losing so much. That's a very common pattern behind "fitter but not faster."

The four usual suspects

What follows is a diagnostic framework rather than a study finding. It's TriForward's synthesis of the evidence in this article and the practical patterns coaches report. The four common limiters are:

1. Propulsive efficiency (technique). Most of your effort isn't turning into forward speed.
2. Session monotony. Every swim is the same steady distance at the same pace, so there's no stimulus to get faster.
3. Frequency. Too few swims a week for a skill-heavy sport, often with long gaps.
4. No measurement. You never test, so you don't know your current threshold pace, can't set targets, and can't see small improvements.

They often overlap. But one usually dominates, and that's where to start.

Limiter 1: technique, and how to tell

Signs that efficiency is your main limiter:

• Your stroke count per length is high, and it barely changes between easy and hard efforts. You're spinning faster rather than holding more water.
• You can't swim 25 m much faster than your steady pace, even fresh. Your top speed and your cruising speed are close together.
• Your legs sink noticeably when you stop kicking, or you rely heavily on a pull buoy to feel comfortable.
• You finish sets breathing hard but feel you're "fighting" the water rather than moving through it.

If several of these apply, technique work with feedback is the highest-value change you can make. That doesn't mean endless drills done without thought. The evidence on drills in adults is thin. A 2025 scoping review of swim-learning methods, mostly in children, concluded that the literature is "scarce, generally atheoretical and of questionable methodological quality." What's better supported is feedback: some way of seeing what your stroke actually does, then changing one thing at a time. TriForward's article "Filming Your Stroke" covers how to get that feedback without specialist equipment.

Limiter 2: the same swim every time

The most common age-group pool session is a continuous swim, or a long set at one comfortable pace, repeated every visit. It builds aerobic base early on, but the stimulus stops changing, and so does your speed.

What does the research say about intensity versus volume? Most trials are in competitive pool swimmers, so the transfer to adult triathletes is uncertain. But the direction is fairly consistent:

• Faude and colleagues (2008) put 10 competitive swimmers through two 4-week blocks in a randomised crossover: high volume at low intensity, and lower volume at higher intensity. Performance over 100 m and 400 m didn't differ between blocks. The authors concluded that, for 4 weeks, high volume had no advantage over lower-volume, higher-intensity training.
• Kilen and colleagues (2014) followed 41 elite swimmers for 12 weeks. One group roughly halved its weekly distance (about 17 km versus 35 km) and did around 5 hours of high-intensity work a week instead of 1, while total training time stayed around 12 hours. Performance and physiological capacity were neither improved nor compromised. Half the distance, with more intensity, gave the same result.
• Piatrikova and colleagues (2020) prescribed high-intensity intervals from each swimmer's own critical speed (a test-derived threshold pace) for 12 national-level swimmers over 15 weeks, on no more than 30 km a week, about 25% less volume than usual. Critical speed improved by about 5.4%, and main-event performance improved by around 1-2%.
• A 2026 meta-analysis by Jin and colleagues pooled 11 studies (237 swimmers, average age about 15) and found high-intensity interval training improved both VO2max and swimming performance, with larger effects in programmes lasting 8 weeks or more.

The populations matter. These are mostly young, technically skilled competitive swimmers, and some studies had only 10-12 participants. An adult triathlete with inefficient technique is a different case. What the evidence does support is that adding structure and intensity to limited pool time is unlikely to cost you and may help, while simply adding more easy metres has little evidence of advantage. For someone stuck at the same pace after months of steady swimming, that's a strong argument for changing the session content before adding volume.

Limiter 3: frequency

There's no trial establishing a minimum number of weekly swims for adult triathletes, so this section is labelled inference. But two lines of evidence point the same way.

First, swim fitness and skill decay quickly. Zacca and colleagues (2019) found that just four weeks without training impaired 400 m performance in 15 young swimmers by about 3.8%, with stroke rate dropping. Swimmers who stayed active in other ways during the break lost less. Detraining over a few weeks is not the same as a few days between sessions. But it supports the idea that long gaps let swim-specific qualities slip.

Second, swimming has a large skill component, and skill learning generally benefits from more frequent practice. Three 40-minute sessions give your stroke three chances a week to rehearse a change. Two 60-minute sessions give it two, with longer gaps for old habits to return.

If you currently swim twice a week and have the option, splitting the same total time into three shorter sessions is a reasonable experiment. If two is all you can do, make both count with clear purposes rather than repeating the same swim.

Limiter 4: you never test

Without a test, you can't set training intensities, and you can't see small improvements. Many age-groupers who think they've "stayed the same for six months" have never actually measured pace under controlled conditions. They're judging from how a steady swim feels, which drifts with fatigue and mood.

The simplest useful test for most triathletes is two time trials, typically 400 m and 200 m, swum on separate efforts with full recovery. A 2023 study by Scott, Burden and Dekerle in 32 national-standard swimmers found that 200 m and 400 m time-trial performances were highly repeatable (coefficient of variation under 2%). The critical speed calculated from them was also reliable (CV under 3.4%). The anaerobic reserve value from the same calculation was not reliable, so don't read much into that second number. The companion article "Critical Swim Speed" explains how to run and use this test.

Testing every 4-6 weeks gives you two things: training paces that move as you improve, and evidence of whether what you're doing is working.

Putting it together: an 8-12 week reset

Here's one way to restructure limited pool time if you've stalled. It isn't a prescription, and it isn't a study protocol. It's a reasonable application of the evidence above for someone swimming two to three times a week.

Week 1: test. 400 m and 200 m time trials on a separate day or with long recovery. Record time and stroke count per length.

Each week, if three sessions are possible:

• Session A, skill. Short repeats (25-50 m) with long rest, each with one technique focus, ideally informed by video or coach feedback. Finish with a few repeats at steady pace holding the new pattern.
• Session B, threshold. Intervals around your test-derived threshold pace, for example 100-200 m repeats with short rest. Total work rises gradually over the block.
• Session C, speed and aerobic. Short fast efforts (25-50 m) with generous rest to practise holding good form at speed, then a steady aerobic set.

If only two sessions are possible: combine A and C into one session and keep B.

Weeks 4-6 and at the end: retest. Update paces. Compare stroke count at the same speed.

Two cautions. First, build intensity and volume gradually, especially if you add paddles. Increases in swim load are linked to shoulder pain in swimmers, and paddle use was associated with shoulder overuse injuries in a study of amateur triathletes (see "Swimmer's Shoulder in Triathletes"). Second, don't change everything at once. If you overhaul technique, intensity and frequency in the same week, you won't know what helped.

What to expect

The research gives some calibration, with the same caveats about population. In the Piatrikova study, national-level swimmers improved critical speed by about 5% over 15 weeks with structured, individualised intervals. The Jin meta-analysis found larger effects in programmes of 8 weeks or more. An adult triathlete starting from lower efficiency may see larger gains from technique change, but technique changes often feel slower before they feel faster.

That's a key point for anyone who has plateaued. When you change your stroke, your pace may dip for a few weeks while the new pattern beds in. That's normal, and it's why testing matters. Judge the change on test results after several weeks, not on how individual sessions feel.

If you're a masters swimmer, the plateau may be hiding progress

Age matters here more than most triathletes realise. Käch and colleagues analysed more than 410,000 Ironman results (329,066 men and 81,815 women) and found that age-related performance decline started earlier in swimming than in cycling or running, from roughly age 25-29 in both sexes. Those are race results from a cross-section of different athletes, not individuals followed over time, so they can't tell you how fast any one person will slow. But they suggest that for an athlete in their 40s or 50s, swim fitness is working against a stronger age-related headwind than bike or run fitness.

So holding the same pace for six months isn't necessarily the same as standing still. It may partly reflect training cancelling out decline. That's an inference, and it's not a reason to accept a plateau. It is a reason to judge progress on controlled tests rather than on memories of how fast you used to be.

Pool pace isn't race pace

One more check before you conclude nothing has changed. Most age-groupers judge progress by pool times, but they race in open water, often in a wetsuit. A 2021 review of 17 studies by Quagliarotti and colleagues found wetsuits improved swimming performance by up to 11%, mainly through lower drag and energy cost and more buoyancy. The size of the benefit varied with swimming ability and wetsuit type. Less efficient swimmers, whose legs sink more, often have more to gain from that extra buoyancy.

The practical point is that your pool pace and your race pace can move somewhat independently. Technique gains made in the pool may show up partly as a smoother, less tiring wetsuit swim rather than a faster pool 400 m. It's worth including an occasional open-water or wetsuit session in your testing if you can do so safely.

When to get outside help

If after one structured 8-12 week block, with honest testing, nothing has moved, it's worth getting expert eyes on your stroke. A qualified swim coach watching from the deck, or reviewing underwater footage, can often spot one or two dominant faults in minutes that months of solo training won't fix. For many plateaued age-groupers, that single intervention is worth more than any change in metres or intensity.

References

• Toussaint HM. Differences in propelling efficiency between competitive and triathlon swimmers. Medicine & Science in Sports & Exercise, 1990;22(3):409–415. PubMed 2381311
• Faude O, Meyer T, Scharhag J, Weins F, Urhausen A, Kindermann W. Volume vs. intensity in the training of competitive swimmers. International Journal of Sports Medicine, 2008;29(11):906–912. doi:10.1055/s-2008-1038377
• Kilen A, Larsson TH, Jørgensen M, Johansen L, Jørgensen S, Nordsborg NB. Effects of 12 weeks high-intensity & reduced-volume training in elite athletes. PLoS ONE, 2014;9(4):e95025. doi:10.1371/journal.pone.0095025
• Piatrikova E, Gonzalez J, Willsmer N, Sousa A, Williams S. Individualizing training in swimming: evidence for utilizing the critical speed and critical stroke rate concepts. International Journal of Sports Physiology and Performance, 2020;15(5). doi:10.1123/ijspp.2019-0546
• Jin R, Chen C, Finlay MJ, Cuenca-Fernández F, Zhong Y, Gao D, Wu Z. The effects of high-intensity interval training on competitive swimmers: a systematic review and meta-analysis. Journal of Science and Medicine in Sport, 2026. doi:10.1016/j.jsams.2026.02.015
• Zacca R, Toubekis A, Freitas L, Silva AF, Azevedo R, Vilas-Boas JP, Pyne DB, Castro FAS, Fernandes RJ. Effects of detraining in age-group swimmers performance, energetics and kinematics. Journal of Sports Sciences, 2019. doi:10.1080/02640414.2019.1572434
• Scott BE, Burden R, Dekerle J. Stroke-specific swimming critical speed testing: balancing feasibility and scientific rigour. Journal of Human Kinetics, 2023;90:239–251. doi:10.5114/jhk/170882
• Minkels C, van der Kamp J, de Vries R, Beek PJ. Learning how to swim in 5- to 12-year-old children: a scoping review of evidence-based motor learning methods. Frontiers in Sports and Active Living, 2025. doi:10.3389/fspor.2025.1505301
• Schorn D, Vogler T, Gosheger G, Schneider K, Klingebiel S, Rickert C, Andreou D, Liem D. Risk factors for acute injuries and overuse syndromes of the shoulder in amateur triathletes: a retrospective analysis. PLoS ONE, 2018;13(6):e0198168. doi:10.1371/journal.pone.0198168
• 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
• Quagliarotti C, Cortesi M, Gatta G, Bonifazi M, Zamparo P, Baldassarre R, Vleck V, Piacentini MF. Wetsuit use during open water swimming. Does it "suit" everybody? A narrative review. International Journal of Sports Physiology and Performance, 2021;16(9):1217–1224. doi:10.1123/ijspp.2020-0808