The phrase "to heat the body" means to raise the temperature of the human body, often by physical activity or exposure to warmth, in order to make it feel warmer and more comfortable. Full definition
In contrast, an infrared sauna session heats your body directly raising your core body temperature as your body absorbs the infrared heat. (infraredsauna.com)
An infrared sauna heats your body from the inside out, which allows you to stay in the sauna longer and increases your heart rate. (fitnessforwardstudio.com)
They are very effective at heating your body core and helping your body detox. (infraredsauna.com)