A good instructor says light, moderate, heavy. A poor one says set the dial to three. Only one of those takes account of the body you actually brought with you.
Fixed settings guarantee that somebody in the room is working far too hard and somebody else is barely working at all. If you tend to go flat out and only notice afterwards, a class that cues by effort protects you from yourself. It is a fair thing to ask about before you sign up, and a decent instructor will not mind being asked.
Qur’an and Sunnah
God does not burden any soul with more than He has given it (Quran 65:7). Measuring what is asked against what this particular person has been given is the principle at work, and a body in a class is no exception.
لِيُنفِقۡ ذُو سَعَةࣲ مِّن سَعَتِهِۦۖ وَمَن قُدِرَ عَلَيۡهِ رِزۡقُهُۥ فَلۡيُنفِقۡ مِمَّآ ءَاتَىٰهُ ٱللَّهُۚ لَا يُكَلِّفُ ٱللَّهُ نَفۡسًا إِلَّا مَآ ءَاتَىٰهَاۚ سَيَجۡعَلُ ٱللَّهُ بَعۡدَ عُسۡرࣲ يُسۡرࣰ ا
and let the wealthy man spend according to his wealth. But let him whose provision is restricted spend according to what God has given him: God does not burden any soul with more than He has given it- after hardship, God will bring ease
Qur’an 65:7read it in the library
Translation: M.A.S. Abdel Haleem, The Qur'an, Oxford University Press, 2004.
What the research says
In a crossover trial with 42 students, three breathing paces were compared and the slowest of the personally set paces produced the most relaxation and the largest drop in physiological arousal. The pace had to be worked out for each person rather than fixed in advance. That is the same principle in a different room, from a small study of healthy students rather than from anything about exercise classes.
Moebus L, Spitschan M, Ehrlenspiel F. (2026). Lower breathing frequencies in personalized slow-paced breathing enhance relaxation and reduce arousal.. iScience doi
Strength of evidence: one line of research. A single study, or a theoretical account.
Why it works
Effort described relative to you fits every body in the room, while a number only fits the person who picked it.
This one is still a draft. It is waiting on a scholar and a clinician to read it before it is published.
Near this one
Four in, hold four, four out, hold four. The holds are the strong part of this one, and they stay optional every single time.
Holding your breath for a moment makes the next one deeper, which sounds backwards until you know why. The urge to breathe is driven by carbon dioxide, not by a shortage of air.
There are two skills here rather than one: letting your body move and settle in its own way, and being able to steer yourself deliberately towards rest or alertness. It is worth having both.