Walking in heat does burn slightly more calories, but the increase is negligible in the context of overall energy expenditure. This marginal increase is due to thermoregulation, the body’s primary mechanism for maintaining a stable internal temperature. When the environment is hot, the body expends a small amount of extra energy to prevent overheating, which adds to the calories burned during physical movement. This extra energy is an overhead cost added to your basal metabolic rate. While the thermal challenge forces the system to work harder, the difference is rarely significant enough to be a meaningful factor in fitness or weight management goals.
The Body’s Heat Regulation System
The minor boost in calorie burn stems from the effort required to maintain the body’s core temperature of approximately 98.6°F (37°C). When walking in a hot environment, muscles are generating heat from movement, and the environment increases the thermal load. To counteract this combined heat gain, the body’s thermoregulatory system, managed by the hypothalamus, initiates a series of cooling responses.
One immediate response is vasodilation, where blood vessels near the skin widen to increase blood flow. This redirects warm blood from the core to the periphery, allowing heat to dissipate into the air. Circulating a higher volume of blood requires the heart to work faster, increasing overall cardiac output and metabolic demand.
The other major component of heat dissipation is sweat production and evaporation, which also requires energy. The energy used to produce sweat and transport it to the skin, combined with the increased cardiovascular effort, represents the “extra” calories burned. This heightened activity from the circulatory system and sweat glands is an additional layer of energy expenditure. However, this energy is solely dedicated to cooling the body and does not contribute to muscular efficiency or movement.
Calculating the Calorie Difference
Although the body works harder in the heat, the number of extra calories burned is minimal and should not be relied upon for meaningful weight loss. The additional energy expenditure is only a fraction of the total calories burned during the walk, often amounting to a negligible difference. For the average person walking for an hour, the effort to stay cool may only contribute a few dozen extra calories at most.
The body is highly adaptable, and this small caloric effect is temporary; the body can acclimate to consistent heat exposure within 7 to 14 days. Once acclimation occurs, the body becomes more efficient at cooling itself, reducing the additional energy required for thermoregulation. Furthermore, the perceived benefit of extra calorie burning is often offset by a necessary reduction in walking intensity or duration.
If the heat causes you to slow your pace or shorten your walk, the overall total calorie expenditure will be significantly lower than a longer or faster walk in a moderate temperature. Increasing factors like walking speed, distance, or incorporating hills are far more effective and reliable methods for increasing total calorie burn than depending on the heat. The energy expended on thermoregulation is largely wasted from a fitness perspective, as it is diverted entirely to heat dissipation rather than fueling muscle contraction.
Safety and Hydration When Exercising in Heat
The marginal increase in calorie burn comes with significant health risks that far outweigh any potential fitness benefit. Exercising in high heat and humidity increases the risk of serious health conditions, including dehydration, heat exhaustion, and heat stroke. The combination of physical exertion and high temperatures stresses the body’s systems, making safety precautions paramount.
Fluid intake requires careful planning, as thirst is a delayed signal of dehydration. Individuals should be well-hydrated before starting their walk and sip water every 15 to 20 minutes throughout the activity. For walks lasting over an hour or involving heavy sweating, replacing lost electrolytes with a sports drink may be advisable.
To minimize heat exposure, schedule walks during the cooler parts of the day, specifically avoiding the period between noon and 3 p.m. when temperatures peak. Wearing lightweight, light-colored, and loose-fitting clothing made from moisture-wicking synthetic fabrics helps cooling mechanisms work efficiently. Recognizing signs of heat stress is crucial. If symptoms such as dizziness, headache, muscle cramps, or dark-colored urine appear, activity must be stopped immediately.