A study of patients with rheumatoid arthritis and ankylosing spondylitis showed a reduction in pain, stiffness and fatigue during infrared sauna therapy.
Some infrared sauna proponents claim that the sauna is an effective method for considerably raising the rate of energy expenditure in the body. Proponents typically quote the Journal of the American Medical Association stating: "A moderately conditioned person can easily sweat off 500 grams in a sauna, consuming nearly 300 kcal, which is equivalent to running 2–3 miles. A heat-conditioned person can easily sweat off 600–800 kcal with no adverse effects. While the weight of the water loss can be regained by drinking water, the calories consumed will not be."
The above statement is based on the amount of energy absorbed by sweat evaporating from the skin. It is equivalent to the latent heat of vaporization of water, which is 539 kcal/kg (2260 kJ/kg). The source of this energy is then confused to be body energy stores, while the source is in fact the excessive heat absorbed from the sauna. The body reacts to the excess heat flux by increasing perspiration.