A long-held notion is that "lactic acid causes muscle soreness". Despite being disproved in the late 70’s, people still love to tout it as the reason for their painful muscles.
Lactic acid is actually a fuel that the muscles actually burn. It’s a help, rather than a hindrance.
Working muscles convert glucose (sugar) or glycogen into it as a byproduct of metabolism. The lactic acid is then taken up and burned further by the cell’s mitochondria – the powerhouses of the cells.
Lactic acid doesn’t ‘build up’ in the muscles causing fatigue. In fact, the muscles ravenously consume it for energy. Nor does it cause the notorious ‘burn’ that people feel at the height of exertion.
Training close to the ‘lactate threshold’ as its known, increases the mitochondria’s efficiency at using up the lactate. This teaches the muscles to burn more of it, thereby allowing them to work harder and longer.
It’s a neat physiologic trick, in that the muscles burn glucose first, and then burn the ‘leftovers’ of glucose. Think of it as the ultimate in energy recycling.
The idea that lactic acid is a caustic waste product was created a century ago. It’s taken many studies to disprove this, yet this notion still hangs on in popular culture.
Oh and next time your muscles are sore a day or more later following a workout; it’s not from the lactic acid. While scientists know that it ISN”T lactic acid, they don’t exactly know what the cause is. More than likely, the pain is a result of micro tears in the muscle. This is known as delayed-onset muscle soreness, or DOMS. Using natural anti-inflammatories like arnica can relieve DOMS.