Exercising in very hot weather significantly challenges the body’s ability to regulate its internal temperature (thermoregulation). In high heat and humidity, the primary cooling mechanism—evaporative cooling through sweat—becomes less efficient. This risks an excessive rise in core body temperature, which can quickly lead to heat-related illnesses. Following safety advice is necessary to avoid thermoregulation failure and maintain well-being.
Pre-Activity Preparation
Planning the timing of exercise is the first line of defense against excessive heat exposure. The hours between 10 a.m. and 4 p.m. typically present the highest temperatures and most intense solar radiation, making early morning or late evening workouts safer choices. This modification minimizes exposure to peak environmental heat stress, reducing the initial physiological strain.
Clothing should actively assist the body’s cooling efforts. Opt for loose-fitting, light-colored garments made from moisture-wicking fabrics. Light colors reflect the sun’s radiation, while loose fits allow air to circulate over the skin, aiding in sweat evaporation. Sunscreen with a high Sun Protection Factor (SPF) should be applied to prevent sunburn, which impairs the skin’s ability to cool itself.
Heat acclimatization significantly improves the body’s tolerance to exercising in heat. This involves gradually introducing the body to heat exposure over 10 to 14 days. The body adapts by increasing sweating efficiency, lowering the core temperature and heart rate response, and stabilizing the cardiovascular system. Initially reducing the intensity and duration of workouts allows the body time to make these physiological changes safely.
Optimal Hydration Strategies
Starting the exercise session in a well-hydrated state is the foundation of any heat-related safety plan. Recommendations suggest consuming approximately 17 to 20 ounces of fluid two to three hours before beginning activity. This pre-hydration allows the body to establish a fluid baseline, which is essential because even mild dehydration of just 2% of body weight can impair performance and thermoregulation.
During the workout, fluid intake should be consistent and frequent, not just based on thirst alone. A general guideline is to consume between 5 to 10 ounces (150 to 250 milliliters) of fluid every 15 to 20 minutes of exercise. For activities lasting less than one hour, plain water is sufficient to replace fluid losses.
For sessions extending beyond 60 to 90 minutes, especially in high heat, sports drinks containing electrolytes become beneficial. Sweat contains sodium, and replacing this electrolyte helps maintain fluid balance and prevents hyponatremia (dangerously low blood sodium). Individuals who are heavy or salty sweaters—indicated by white residue on clothing—may consider using salt tablets or higher-sodium sports drinks.
Modifying Exercise Intensity
Exercising in heat requires a downward adjustment of intensity to lessen the metabolic heat load the body must dissipate. Reducing the pace or distance from a normal routine manages the increased strain on the cardiovascular system. The heart works harder to circulate blood both to the working muscles and to the skin for cooling. This causes the heart rate to rise higher than in cooler conditions for the same effort.
Instead of relying on a fixed pace, use the Rating of Perceived Exertion (RPE) or monitor your heart rate to gauge intensity. The feeling of effort will be disproportionately higher in the heat due to elevated physiological strain, so maintaining a comfortable RPE helps prevent overexertion. Incorporating frequent rest breaks, preferably in the shade, allows the core temperature to drop and gives the body a reprieve from thermoregulatory demands.
Humidity significantly worsens the danger of heat by limiting the effectiveness of sweat evaporation. When the air is saturated with moisture, sweat cannot turn into vapor easily, making the body feel hotter and causing the core temperature to rise more rapidly. Being aware of the Heat Index, which combines air temperature and relative humidity, offers a more accurate assessment of the risk and can help inform the decision to reduce or postpone the workout.
Identifying and Responding to Heat Illness
Recognizing the early warning signs of heat-related illness is paramount for preventing a medical emergency. Heat cramps, often the first sign, are painful muscle spasms, typically in the legs or abdomen, occurring during or after exercise. Immediate treatment involves stopping the activity, resting in a cool place, and consuming fluids containing electrolytes.
Heat exhaustion is a more serious condition characterized by heavy sweating, paleness, weakness, dizziness, nausea, and a fast, weak pulse. The skin may feel cool or clammy despite the heat. If suspected, the person must be moved to a cool environment and lay down with feet slightly elevated. They should receive cool, wet cloths applied to the skin and sip water or a sports drink. If symptoms worsen or vomiting occurs, immediate medical attention is necessary.
Heat stroke is a life-threatening emergency requiring immediate professional medical intervention. Signs include confusion, slurred speech, loss of consciousness, and a very high body temperature, often above 103°F (40°C). The skin may be hot and red, and, contrary to heat exhaustion, sweating may have ceased. Call emergency services immediately, move the person to the coolest possible area, and begin aggressive cooling efforts, such as applying ice packs or cold, wet towels to the armpits, neck, and groin.