Why Are My Muscles Sore After Working Out?

By: Yuri Elkaim, BPHE, CK, RHN


Performing a bout of unfamiliar exercise often results in sore muscles. If you've experienced sore muscles after working, you'll know what I'm talking about. This phenomenon is known as "delayed onset muscle soreness" or DOMS.

This is particularly prominent when your workouts involve eccentric contractions. This is when your muscles are lengthening while contracting. Examples of this include the "negative" motion (or when the weight is lowered) doing biceps curls or bench press. Essentially, the muscle fibers are being "ripped apart" at the same time that they're contracting. This leads to muscle damage. But it's also how your muscles get stronger.


Protection Against Feeling Sore After Your Workouts

Interestingly, following recovery from this muscle soreness, a subsequent bout of the same exercise results in minimal symptoms of muscle injury and soreness. This is called the "repeated bout effect". Although this concept has been known for more than 40 years, the exact mechanism(s) responsible for this exercise-induced protection are still unknown.

There have been 3 theories that have been put forth to try to explain this protective mechanism known as the "repeated bout effect". They are the neural theory, connective tissue theory, and cellular theory.


The Neural Theory

The neural theory proposese that the exercise-induced muscle injury occurs in a relatively small number of fast twitch (type II) fibers. In the subsequent exercise bout, there is a change in the pattern of recruitment of muscle fibers to increase motor unit activation to recruit a larger amount of muscle fibers. This results in the contractile stress being distributed over a larger number of muscle fibers. Hence, there is less stress per muscle fiber and no injury occurs during subsequent workouts.


The Connective Tissue Theory

This theory argues that muscles damage due to the initial workout results in an increase in connective tissue to provide more protection to the muscle during the stress of working out. This increased connective tissue is assumed to be responsible for the repeated bout effect.


The Cellular Theory

This theory predicts that the exercise-induced muscle damage results in the creation of new proteins that improve the integrity of the muscle fiber. The synthesis of these protective proteins reduces the strain on the muscle fiber and protects the muscle from feeling sore after your workouts.


Which one of these theories is most accurate is unknown. In the meantime, each one may play a role in protecting your muscles from getting sore after that initial workout.

So the take home message is that if your muscles feel sore after your first workout, then simply continue working out. Doing so will put these protective mechanisms into effect and will prevent you from any further muscle soreness. In fact, most muscle soreness goes away within 2-3 days of a workout and the more you offer your body different workout routines, the less soreness you'll experience as your muscles become accustomed to more ranges of motion of and varying exercises.

So now you know the answer to why you get sore muscles after working out. More importantly, you now know how to prevent it!


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