Lactic acid and muscle stiffness
Lactic acid is a big organic molecule that is created when glucose is broken down to produce energy without oxygen. It is mainly a muscular metabolic waste but it can also be found in milk products, wine and few lacto-fermented vegetables.
Muscles need energy to move and function. To produce contractions they need oxygen. If there is enough oxygen there will be very few wastes, but if there is not enough oxygen brought in the muscle there will be lactic acid created from the energy production. The more this acid accumulates in the muscle, the more we will feel pain and the less performant we will be.
When too much lactic acid is released in the muscles during effort and we feel the burn, the best thing to do is to reduce the effort intensity and recuperate for a few minutes while the blood is loading up with the lacking oxygen. When lactic acid meets with oxygen again, it transforms and produces CO2 and water, and it will allow more energy to be produced (ATP molecules, readily usable energy currency) and allow you to continue the effort.
In long periods of medium to low intensity effort, long distance runners for instance, there is no production of lactic acid because there is a lot of oxygen that gets to the cells and help ATP synthesis for more energy. This process uses glucids and lipids to create energy, it is therefore the most efficient for fat burning!
Then there is the high intensity effort that last for 1 to 2 minutes, 400 to 800m races for instance. This process releases a huge quantity of lactic acid in the muscles. ATP is also produced with glycolisis, withouth oxygen. Muscles will stop functioning when their acidity level is too high. If that happens we have to wait for the circulation to wash away the extra lactic acid so that the muscular contractions occur again.
Combined with a lack of oxygen, it’s the break down of sugars (glycolisis) that will produce pyruvic acid that will transform into lactic acid. The lactic acid is first saturated in the cell then crosses its membrane and dive into blood circulation, where the liver will eventually recycle it. An hour after exercice, the lactic acid in muscles is all gone, so it is not to blame for being sore the next day. Take note that the more fit you are, the more you will be tolerant to lactic acid’s effects on the body.
During high intensity and short time effort, such as sprints or bodybuilding activity, the energy is produced without oxygen but won’t generate lactic acid because it’s creatine phosphate that is used. Sprinters have to wait several minutes between sprints because they need to restore creatine phosphate inside their muscles. Creatine phosphate can be found in the cells and is necessary for an intense effort but barely lasts 10 to 15 seconds or slightly more depending on the fitness level of the athlete.
All three processes of effort can mix and interact, causing cramps or muscular stiffness if the lactic acid level gets too high. That being said, what causes these muscular issues are mostly the lack of nutrients and/or water, too much proteins and other acidic foods/drinks that will elevate acidity levels in the body. The main solution is to eat plenty of fruits and vegetables, drink lots of water and add magnesium (e.g. sesame, almonds) to your diet. The lack of magnesium can be the cause to your cramps!
Stretching is also a must to evacuate metabolic wastes such as lactic acid. Lactic acid is completely gone from muscles an hour after exercice is done, so it can’t be blamed for the next day’s soreness and stiffness, these are due to microlesions in the muscle fibers. In this case, we have to stretch very gently to not worsen the small lesions. In any case, you must always stretch once you’re well warmed up, at the end of the activity. Stretching also provides drainage and improves circulation through compression/release effect, nutrients and oxygen can then come feed and repair the muscles freely.
Hoping I made it clearer for you on these fascinating processes,
Enjoy your training!