To many individuals performing strenuous physical activities, today’s word used to be synonymous with, well, pain. On the bright side, a better understanding of the various steps of the metabolic pathway has absolved our word of most of the blame – not that it makes the soreness go away any faster. Still, this is no reason for today’s word to fade into obscurity: being a billion-dollar industry (lactic acid is used heavily in the food and pharmaceutical industry) with a global market expected to reach 1,844.56 kilo tons by 2022, it’s a lot more essential than you may think.
An adjective meaning ‘procured from milk’, our word lactic has its origin in the French lactique, which is derived from Latin lac/lactis, meaning ‘milk’. Termed “lactic” from sour milk first used by Swedish chemist Carl Wilhelm Scheele in 1780 to isolate it, the most common use of today’s word is in the form of CH3CH(OH)CO2H or, if you prefer, lactic acid.
First appearing in English through Robert Kerr’s same-year translation of Antione Lavoisier’s 1789 work, Traité Elémentaire de Chimie (Elements of Chemistry), which can be considered the first modern textbook on the subject, our term is simply named as, “Lactic acid”, meaning the acid formed in sour milk.
A little more than half a century after the initial discovery, the observation of the role of Lactobacillus (bacteria) played in the synthesis if lactic acid was noted by Louis Pasteur in 1856, paving the way for commercial production by Boehringer Ingelheim at the turn of the century and leading to the other main understanding of our word – discussing products containing a high proportion of lactic acid – which was first put forth in an advertisement in a 1910 issue of Health & Strength magazine, mentioning: “Lactic St. Ivel Cheese contains the pure Bulgarian bacilli in great abundance.”
Beyond this century-old ad, many of our favourite dairy products, such as yogurt, kefir, and cottage cheese, involve the use of lactic acid; moreover, lactic acid has a hand in the flavour of sourdough bread and some of our favourite fermented beverages, like wine and beer (Belgian Lambics, Berliner weisse, and American wild ale, for example). Even when not enhancing the taste, lactic acid has been widely used as a food preservative, curing agent, or, in the case of meat processing, a decontaminating agent.
Getting back to the initial (and now broken) link between lactic acid and muscle pain, the story began with Jöns Jacob Berzelius finding in 1808 that lactic acid is produced by muscles during physical exertion. Essentially this is true: when exercised at capacity, the muscles are not able to convert food to energy due to lack of oxygen, leading to anaerobic respiration, the production/accumulation of lactic acid as a by-product, and that burning sensation. Unfortunately, while studying glycolysis in the 1920s, several assumptions were made by researchers that linked short-term lactic acid build-up with the more intermediate-term acidosis and Delayed Onset Muscle Soreness (DOMS), which led to greater importance being placed on hydration, and the “warm-up”/”cool down” phase of exercise.
While hydration, stretching, and post-workout rest are still important, recent studies have shown that lactic acid, though it may cause a burning sensation during the workout, is quickly flushed out of the muscles during and after the workout. The actual cause of this muscle tenderness several days after a workout is mostly due to small micro-tears in the muscle fibre from extended use: in other words, it’s just the typical increasing and strengthening of muscle mass that causes soreness, not the lactic acid.