Science
Open water vs pool swimming: key differences for coaches
8 min readApril 3, 2026
Drafting, thermoregulation, pacing without a clock: 5 physiological and tactical differences every coach must understand between open water and pool swimming.
Drafting, thermoregulation, pacing without a clock: 5 physiological and tactical differences every coach must understand between open water and pool swimming.
If you coach swimmers who compete in both pool and open water events, you already know the two environments feel completely different. But knowing why they differ, and what that means for your training plan, is what separates a reactive coach from a prepared one. Research shows that drafting behind another swimmer in open water can reduce energy expenditure by 18 to 25 percent. That single factor alone changes race tactics, training priorities, and how you prepare athletes for competition.
The physiological demands are not the same. Pool swimming happens in a controlled environment: constant temperature, no currents, turns every 25 or 50 metres, clear visibility, a pace clock on the wall. Open water removes all of that. The swimmer must sight, navigate, tolerate cold, manage contact with competitors, and pace internally without external cues. These are trainable skills that require deliberate practice.
Understanding these five differences helps you decide what to train, when, and in which environment.
In pool swimming, push-offs contribute significantly to total speed, especially in shorter events. A 100-metre pool swimmer may spend up to 30% of race time in the glide phase after each turn. In open water, that advantage disappears entirely. Open water swimmers need greater sustained aerobic power per metre covered, and turn-related drills transfer very little to open water racing.
Competition water for open water events ranges from 16°C to 31°C under World Aquatics rules. Cold water below 20°C increases metabolic demand: the body burns more energy maintaining core temperature. A study published in the European Journal of Applied Physiology found blood lactate was higher during swimming in 23°C water compared to warmer conditions, suggesting cold exposure adds physiological stress on top of the swimming effort. Cold acclimatisation sessions belong in the preparation phase for any open water competition.
The 18 to 25% energy saving from drafting is not just a statistic. It means that a swimmer in a pack is effectively swimming at a lower physiological cost than the leader. Training for this means practicing group swimming, learning to read the pack, and developing the ability to surge suddenly when a gap opens.
Pool swimmers use the pace clock, lane lines, and the wall as feedback. Open water swimmers have none of these. Research on self-paced exercise consistently shows that athletes without external feedback tend to start too fast and fade in the second half. Teaching swimmers to calibrate their perceived effort with their actual speed is a specific skill, not a natural one.
Lifting the head to sight a buoy disrupts body position and increases frontal drag. Each head lift breaks the streamline, reducing stroke efficiency. Competitive open water swimmers typically sight every 8 to 12 strokes. Coaches should drill sighting technique independently, then integrate it progressively into longer sets to minimise the efficiency cost.
| Factor | Pool | Open water |
|---|---|---|
| Turns / push-offs | Every 25-50 m (key advantage) | None |
| Water temperature | 26-28°C (controlled) | 16-31°C (variable) |
| Drafting effect | Minimal | 18-38% energy saving |
| Pacing feedback | Clock, walls, lane lines | Internal only |
| Sighting required | No | Every 8-12 strokes |
| Currents / navigation | None | Variable — must adapt |
Pool-based training remains the backbone of aerobic development. Interval precision, pace tracking, and technique work are all easier to control in the pool. Use the pool for structured Zone 2 sets, lactate threshold work, and stroke technique drills. See the article on Zone 2 and lactate threshold in swimming for programming guidance.
Open water sessions serve different purposes: navigation practice, pack swimming, pacing calibration, sighting technique, cold water exposure, and mental preparation. A well-designed programme for open water competitors allocates at least two open water sessions per month during the build phase, increasing to weekly in the competition phase.
"The biggest mistake pool coaches make when preparing swimmers for open water is assuming that pool fitness transfers automatically. The fitness transfers. The skills do not."
— Open Water Swimming, Springer Nature (2018)
A structured transition block for pool swimmers entering their first open water season:
| Phase | Focus | Key sessions |
|---|---|---|
| Weeks 1-2 | Cold water exposure, sighting basics | Open water entry + 30 min aerobic with sighting every 10 strokes |
| Weeks 3-4 | Pack swimming, pacing without clock | Group sets, perceived-effort intervals, navigation landmarks |
| Weeks 5-6 | Race simulation | Mass start, buoy turns, 1-2 surges per km, wetsuit practice |
Wetsuit use also changes biomechanics. Wetsuits increase buoyancy, raising the hips and reducing the kick workload. Swimmers often find their freestyle technique feels different because the buoyancy changes their natural body position. This can benefit athletes with low hips in the water, but it also means that technique cues developed in the pool may need adjusting. Always practice in the wetsuit before race day, not for the first time on it.
A swimmer with a strong aerobic base and high lactate threshold will perform well in both environments because the fundamental energy systems are the same. A PubMed study (2025, PMID 39788117) on world-class open-water swimmers found a mean lactate threshold velocity of 1.62 m/s, comparable to elite pool middle-distance swimmers. The physiological base is shared across both disciplines.
What does not transfer automatically is open water skill: navigation, pack dynamics, pacing without cues, and cold tolerance. These require specific practice regardless of pool fitness level. A national-level pool swimmer entering a 10 km open water race without preparation can expect to underperform relative to a technically weaker swimmer with open water experience.
320+ active coaches · 7,500+ training sessions · Since 2017
Plan your pool and open water sessions side by side in Padlie. Assign environments to each workout, track volume by discipline, and keep your athletes' progression visible across both. Free plan, permanent.
Try for free →Sources