Dehydration in Athletes

Overview

Dehydration occurs when the body loses more fluid than it takes in. During physical exertion, the body loses fluid through sweating, breathing and urination. Even a small reduction in hydration levels — as little as 2% of body weight — can cause a significant decrease in athletic performance, cognitive function and thermoregulatory capacity.

Dehydration is common at outdoor sporting events, particularly in warm weather, and affects athletes across all disciplines including polo, cycling, equestrian sport and endurance running. Severe dehydration can become a medical emergency requiring urgent intervention.

Common Causes

• Insufficient fluid intake before or during physical activity
• Prolonged exertion in hot or humid conditions
• Heavy sweating without adequate fluid replacement
• High-intensity exercise reducing the opportunity to drink
• Gastrointestinal illness causing vomiting or diarrhoea
• Consumption of alcohol or caffeinated drinks before activity
• Failing to recognise or respond to early signs of dehydration

Signs and Symptoms

Mild to moderate dehydration:

• Thirst
• Dry mouth and lips
• Dark yellow urine
• Reduced urine output
• Headache
• Fatigue and reduced performance
• Dizziness or light-headedness
• Muscle cramps

Severe dehydration:

• Extreme thirst
• Very dark or no urine output
• Rapid heartbeat and breathing
• Confusion or altered mental state
• Sunken eyes
• Cool, clammy skin
• Fainting or collapse

Immediate Actions

• Move the athlete to a cool, shaded area
• Encourage gradual rehydration with water or an isotonic sports drink
• Do not give large volumes of water rapidly — sip steadily
• Rest the athlete and avoid further physical exertion
• Loosen or remove unnecessary clothing
• Monitor for improvement over 30–60 minutes
• If oral fluids are not tolerated or cannot be taken, seek immediate medical assistance

When to Call Emergency Services

Event Environment Considerations

Dehydration is a significant and preventable risk at outdoor sporting events and competitions:

• Hydration stations should be positioned at regular intervals throughout event venues
• Fluid intake opportunities should be built into competition schedules at appropriate intervals
• At equestrian and polo events, athletes and horses are both at risk — provision for both should be planned
• In cycling sportives and road races, feed stations and fluid drops are an essential component of medical planning
• Medical teams should carry intravenous fluid capability for severe dehydration management
• Coaches and team staff should encourage athletes to drink before they feel thirsty

Prevention Advice

• Begin activity in a well-hydrated state — monitor urine colour from the morning of competition
• Drink 400–600ml of water in the 2 hours before exercise
• During prolonged exercise, aim to replace approximately 80% of sweat losses
• Electrolyte drinks are beneficial for exercise lasting more than 60–90 minutes
• Avoid alcohol and excessive caffeine in the hours before competition
• Weigh yourself before and after training — each 1kg of weight lost represents approximately 1 litre of fluid deficit
• After exercise, rehydrate at a rate of approximately 1.5 times the fluid deficit

When to Seek Medical Assessment

Mild dehydration will typically resolve with rest and oral fluid replacement. Medical assessment should be sought in the following circumstances:

• Symptoms do not improve after 1–2 hours of rest and rehydration
• The athlete is vomiting and unable to retain fluids orally
• There are signs of severe dehydration including confusion or collapse
• The athlete has an underlying medical condition
• Recurrent episodes of significant dehydration affecting performance