Sore Muscles and Lactic Acid, Concerning Exercise Pain

I go to the gym to lift weights around 4-5 times per week. I’m writing this blog approximately 48 hours after I fully exerted myself, working my chest muscles. Because it was a particularly lengthy workout, I am still experiencing some muscle discomfort and soreness. I’m using this blog to determine the causes of muscle soreness from strenuous exercise and examine how the human body reacts to exercise.

Firstly, let’s differentiate between the 3 types of exercise pain. There is pain experienced either during or immediately after exercise, delayed-onset muscle soreness, and pain brought upon by muscle cramps. The first and third types of pain are rather self-explanatory, however, delayed-onset muscle soreness (DOMS) is an entirely different beast. DOMS is induced only by extreme muscle lengthening during exercise, and is not felt during exercise. Some prime examples of when one might experience DOMS include tightness after running downhill or lifting heavy weights, marking it as the type of soreness I am currently undergoing.

During exercise the human body does all sorts of things to try and regulate bodily functions. There are many common misconceptions about the buildup of lactic acid, including that it is the culprit for muscle soreness. Rather, there are several steps the body goes through to produce and cleanse the system of lactic acid. As we being to work out, the body strives to bring in more oxygen, so our muscles can function aerobically. However, there comes a time when the oxygen is not enough to fuel the muscles. At that point, muscles need to continue to function without the help of oxygen. The solution? Muscles begin to operate anaerobically, that is, work by breaking down sugars instead of relying on oxygen. This process causes the production of lactic acid, which does not causes muscle pain as popular belief suggests, but acts as a type of fuel for muscles to absorb.

The lactic acid produced during the workout is actually flushed out of the body within an hour or so, while the pain does not set in until 24-48 hours later, putting to rest the theory that lactic acid causes DOMS. Exercises such as lifting weights actually create micro-tears (small muscle “damages”) in the muscle fibers, which mend themselves to become increasingly resilient and opposed to tearing. After enough of this buildup, a lifter like myself is able to lift more and more weight because the muscle is stronger, and the micro-tearing procedure repeats itself.

The process from which the micro-tears occur is fueled by the body’s capability to generate lactic acid. All of this happens before the body and muscles actually feel the onset of DOMS. The pain then comes primarily from two factors: (1), the damaged muscles release chemicals that set off pain receptors, and (2), the muscles stimulate an increased blood flow to the area of damage, which causes swelling and soreness.

How muscles perform with and without oxygen, Link to page

This graphic determines the type of muscle respiration being experienced while looking at different stages of breathing, Link to slideshow

Changes is muscles during vigorous contractions Link to slideshow

One thought on “Sore Muscles and Lactic Acid, Concerning Exercise Pain

  1. Claire E Going

    Hi Nicholas,
    This was an intriguing post because everyone has experienced delayed-onset muscle soreness the day after (or usually in my case, two days after) an intense workout. To see the breakdown of what is happening on a chemical and cellular level with micro tears and lactic acid is very interesting, but I think this post could go further with the study and figure out why sometimes we feel more pain 48 hours after a workout as opposed to 24 hours. Or, the best ways to decrease muscle soreness and why they help on a chemical level. Here is an article I found on “how to beat DOMS” and why these techniques work. Great article!
    -Claire

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