Bikram Yoga: Relationship Between Heat & Humidity

Bikram yoga, or hot yoga, is a style of yoga in which the physical postures are practiced in a classroom with elevated heat and humidity. Classes consist of a 26-posture series practiced in 105-degree Fahrenheit heat with 40 to 60 percent humidity. Heat and humidity, when combined, provide a unique physiological challenge to the body, making it harder to prevent possibly dangerous increases in core temperature.

  1. Hot, Hot, Hot

    • During exercise of any kind, heat produced by the working muscles causes an increase in the body’s core temperature. A small rise in core temperature is normal due to increased heat production. However, a rise in core temperature beyond 102 to 104 F can be potentially dangerous. Therefore, to prevent this from occurring, the body increases heat loss through radiation, convection and evaporation, each of which is compromised in a hot and humid environment such as a Bikram yoga class.

    Horses Sweat, Men Perspire, Women Glow

    • Sweating is an effective heat loss method during exercise. Blood is diverted away from the internal organs to the skin, where the evaporation of sweat cools the surface of the skin. When blood comes into contact with the cooled skin, it then travels back toward the body's core to cool the internal organs and tissues. This helps to prevent a dangerous rise in core temperature during exercise. Humidity prevents the sweat from evaporating, however, and thus, the surface of the skin is not sufficiently cooling the blood flow being directed there. Sweat is only effective in cooling the body when it is able to evaporate from the surface of the skin.

    The Convection Effect

    • Convection is the loss of heat through air coming into contact with the body. This method of heat loss depends on the difference in temperature between the body and the environment and is most effective when the environment is cooler than the body’s core temperature. In a Bikram yoga classroom, the temperature is 105 F, which is significantly higher than that of the body, which typically stays around 98.6 F or a little higher during exercise. Therefore, both sweating and convection heat loss mechanisms are compromised in Bikram yoga.

    Get Used to It

    • According to the 2007 American College of Sports Medicine position stand on "Exertional Heat Illness During Training and Competition," just two weeks of training in the heat reduces the risk of heat exhaustion or illness by improving the body's capacity to maintain electrolyte balance and improving cardiovascular function. Specific changes in the body that take place are increases in sweat rates and earlier onset of sweating; decreased sodium content in the sweat, minimizing the loss of electrolytes; and decreased resting body core temperature, lowering the chance of a dangerous rise in temperature during exercise. While no study has looked into a training effect of Bikram yoga specifically, it is presumable that these same adaptations take place with regular yoga practice in the heat.

    Things to Consider

    • Given the challenge of the heat and humidity to the body’s thermoregulation capabilities, it is important to proceed with caution when practicing Bikram yoga or any other exercise in a hot, humid climate. Maintaining hydration levels is of vital importance when practicing this form of yoga. Hydration is best before class, as going in dehydrated will only further increase the risk of heat illness or stroke by lowering sweating rates. Knowing the signs of heat exhaustion is also important: They include weakness; cold, pale or clammy skin; rapid, weak pulse; nausea or vomiting; and fainting.