When summer arrives, vast bodies of water become the arena for one of the most demanding sports: open water swimming.
This article explores the fascinating science that governs performance and safety in this extreme endurance sport.
Unlike the predictable, calm waters of a pool, open water racing pits athletes against dynamic elements like changing currents, fluctuating temperatures, and challenging waves. This article explores the fascinating science that governs performance and safety in this extreme endurance sport, revealing how elite swimmers adapt and thrive in these unpredictable environments.
At its core, open water swimming is a battle against hydrodynamic drag—the resistance water exerts on a moving body 6 .
Water conducts heat away from the body 25 times faster than air , drastically altering the body's ability to regulate temperature.
In a pool, swimmers minimize drag with streamlined techniques and wall turns. In open water, they face additional resistance from waves and currents, making propelling efficiency (the effectiveness of converting energy into forward motion) a critical factor 6 .
In cold water, rapid heat loss can lead to hypothermia. Conversely, in warm water, the body struggles to cool down, as the primary cooling mechanism on land—sweat evaporation—is virtually useless when submerged 8 .
Risk of hypothermia due to rapid heat loss
Risk of heat illness as body struggles to cool
A pivotal area of research involves the equipment that gives swimmers an edge. A 2021 case study published in the International Journal of Sports Physiology and Performance offered a detailed biomechanical and energetic comparison between swimsuits and wetsuits in elite female open-water swimmers 1 .
Three elite female open-water swimmers were tested one week before a major international competition. Each athlete completed two identical testing sessions—one wearing an Arena Powerskin R-EVO Closed Back swimsuit and the other wearing an Arena Carbon Triwetsuit (both approved by World Aquatics).
The testing protocol was comprehensive 1 :
The study revealed clear and significant benefits from wearing a wetsuit 1 :
This experiment underscores that modern wetsuits do more than just keep swimmers warm; they fundamentally alter the swimmer's interaction with the water.
| Performance Metric | Swimsuit | Wetsuit | Change | Visualization |
|---|---|---|---|---|
| Energy Cost | Baseline | 2% - 6% lower | More Efficient | |
| Drag Factor | Baseline | 14% - 30% lower | More Hydrodynamic | |
| Performance Time | Baseline | 2% - 3% faster | Faster | |
| Stroke Rate | Baseline | 2% - 8% higher | Different Technique |
Data averaged across three elite swimmers 1
Summer races often mean warm water, which presents a severe physiological challenge. Research highlights that swimming in warm water is associated with significant cardiovascular strain 8 .
The high metabolic rate of elite swimmers (with oxygen consumption often exceeding 3.2 liters per minute) generates immense internal heat.
Unlike on land, this heat cannot be dissipated through sweat evaporation. Instead, the body relies almost entirely on convection.
As water temperature increases, the skin-to-water temperature gradient narrows, drastically reducing the body's ability to cool down 8 .
20°C (68°F)
Low Risk26°C (79°F)
Moderate Risk32°C (90°F)
High RiskStudies monitoring core temperature during swimming in water at 32°C (89.6°F) have shown that some athletes can exceed a core temperature of 39.0°C (102.2°F), which is considered high risk for exertional heat illness 8 .
| Physiological Parameter | Response in Warm Water | Risk Level |
|---|---|---|
| Core Temperature | Can rise above 39.0°C (102.2°F) | High |
| Heat Loss Mechanism | Blunted evaporative cooling | Moderate |
| Cardiovascular System | Elevated heart rate; blood flow competition | Moderate |
| Sweat Rate | Can exceed 1 liter per hour | High |
Data based on research findings 8
This risk was tragically highlighted by the death of elite swimmer Fran Crippen in 2010, which led World Aquatics to establish a maximum water temperature threshold of 31°C (87.8°F) for competition cancellation 8 . However, scientists argue that a single temperature threshold is an oversimplification, and future policies must account for other factors like humidity, solar radiation, and race distance to better stratify risk 8 .
Success in open water swimming depends on a combination of physical conditioning, technical skill, and the right equipment.
Provides buoyancy, reduces hydrodynamic drag, and offers thermal protection 1 .
A tethered, inflatable buoy that increases swimmer visibility to boats and provides emergency flotation .
Feature heads-up displays to show real-time metrics like pace, distance, and heart rate 9 .
Monitor stroke rate, SWOLF (swimming efficiency score), heart rate, and course navigation 9 .
Repeated exposure to heat during training to prepare the body's thermoregulatory systems 8 .
Consuming cold fluids and pouring water over the head can help manage core temperature 8 .
Open water swimming is a complex dance of human endurance and environmental forces. Scientific research continues to deepen our understanding of the physiological, biomechanical, and environmental factors at play.
From optimizing wetsuit design to developing more sophisticated safety policies for warm-water racing, science is helping athletes push the boundaries of performance while prioritizing their health.
As research advances, we can expect even more innovative training methods and technologies to emerge. This knowledge not only empowers elite athletes but also enriches the experience for all who are drawn to the unique challenge and beauty of swimming in nature's vast pools.