You smash a workout, and two days later you can barely walk down stairs, and the explanation everyone gives is lactic acid: it built up in your muscles, and now it is sitting there making them ache. Gym lore, repeated by trainers and footy coaches for decades. Stretch it out, flush the lactic acid.
Lactic acid is not what makes you sore the next day. During hard exercise your muscles do produce lactate, but it is cleared away and largely used as fuel within about an hour of stopping; it is long gone by the time the soreness peaks a day or two later. That delayed ache, properly called delayed onset muscle soreness or DOMS, is caused by tiny tears and the resulting inflammation in muscle fibres from unfamiliar or intense effort, especially the lowering, lengthening parts of a movement. It is part of how muscles repair and adapt. Lactate, far from being a villain, is now understood as a useful energy source that even helps buffer fatigue. So 'flushing out the lactic acid' is treating a problem that does not exist; the real soreness is micro-damage healing. Gentle movement, time, and not going from zero to hero in one session help. Blaming lactic acid is just blaming the wrong molecule.
Reception
- Wikipedia: Lactic acidPRIMARY
- Wikipedia: Delayed onset muscle sorenessREFERENCE