Heated yoga studios operate at temperatures well above ordinary room conditions, sometimes with added humidity. The heat changes several distinct physiological variables simultaneously, and separating them explains what the room does and does not accomplish.
Warm tissue behaves differently under stretch
Connective tissue and muscle become more compliant as temperature rises, meaning a given stretching force produces more elongation.
Muscle temperature increases from the muscle's own activity during exercise, and external heat adds to that from the outside rather than replacing it.
The greater range achieved in a heated room is therefore partly a temporary tissue property rather than a lasting change in flexibility.
Heat alters what the range limit feels like
The end of a comfortable stretch is set substantially by sensation, a tolerance limit rather than a mechanical stop in most healthy joints.
Heat modifies the sensory experience of stretch, so a person may move further into a position before the familiar signal to stop arrives.
That is why heated practice carries a specific caution about moving beyond a joint's usual working range with less warning than usual.
Humidity blocks the cooling route
Evaporation of sweat is the dominant mechanism for shedding heat during exercise, and its effectiveness depends on the humidity of the surrounding air.
In a humid room, sweat production continues while evaporation is impaired, so fluid is lost without delivering the corresponding cooling.
Core temperature and heart rate consequently rise more than the mechanical work of the class alone would produce.
Cardiovascular strain increases independently
To move heat to the skin, blood flow is redirected toward the surface, which competes with the demand from working muscle.
Heart rate rises to maintain output under that competition, and continued fluid loss reduces plasma volume, compounding the effect over a long class.
A heated class can therefore register as strenuous on a heart rate monitor while the muscular work performed remains modest.
What the heat does not establish
Sweat volume reflects thermoregulation rather than energy expenditure or any clearance process, so it is not a measure of what the session accomplished.
Weight recorded immediately after a heated class largely represents fluid loss that returns with rehydration.
People who are pregnant, have cardiovascular conditions, or take medications affecting heat tolerance or fluid balance should discuss heated practice with a physician before starting, since the added strain is the point of the format.