Heated yoga is widespread in American studios, with rooms held well above ordinary indoor temperature. The heat changes several things measurably, and changes fewer things than is often claimed.
Heat shifts the load onto circulation
Maintaining core temperature in a hot room requires directing blood toward the skin for cooling, which competes with the demand from working muscles.
Heart rate consequently rises for the same movement, and effort feels harder than the same sequence performed in a cool room.
The intensity experienced is therefore partly thermal rather than mechanical, which explains why a heated class can feel demanding while involving modest muscular work.
Tissue warmth changes stretch tolerance
Warmer tissue is somewhat more compliant, and warmth also raises the threshold at which a stretch registers as uncomfortable.
Both effects allow greater range of motion during the class, and much of that increase reflects altered sensation rather than lasting structural change.
This is why a person can reach further in a heated room and find the following morning's range unchanged, and why heat carries a risk of pushing past a safe limit.
Fluid and electrolyte losses are real
Sweat rates in a hot room can be substantial, and losses include electrolytes as well as water, which matters over a long class.
Symptoms including dizziness, nausea, headache and confusion indicate that thermoregulation is struggling and are reasons to leave the room.
People taking medications affecting fluid balance or heat tolerance, and those who are pregnant or have cardiovascular conditions, face different risk and should consult a physician.
Detoxification claims do not hold
Sweat is primarily water and electrolytes, and its function is temperature regulation rather than the elimination of metabolic waste.
Filtering and clearance are performed by the liver and kidneys, and sweating more does not increase what those organs remove.
The claim persists because heavy sweating feels consequential, and because weight lost during a class is fluid that returns on rehydration.
What heat genuinely provides
Consistent conditions across sessions make classes predictable, and many practitioners find heat mentally clarifying and enjoyable in a way that sustains attendance.
Enjoyment is not a trivial benefit, since the practice a person actually returns to is the one that has any effect at all.
The honest description is that heat changes the experience and the immediate physiology, not that it produces effects the same movements would otherwise fail to produce.