The translation has has been abridged only to the extent of eliminating uninteresting biochemical derail.
Lactic acid is produced in large quantities by heavy, high physical loads.
This widespread opinion rests on speculation asserted several decades ago and never proved, that we today know is highly unlikely. A completely different view, widespread in Anglo-American circles, is that muscle soreness originates through small strains or tears in the muscle tissue. Electromicroscopic research over the past few years has confirmed this proposition. Muscle soreness typically appears after unaccustomed or especially hard muscular endeavor. It comes on after one day and lasts up to a week.