Fatigue is unavoidable when it comes to exercise. That familiar feeling of numbness that overwhelms your muscles indicates for some that it’s time to stop, but others may push through the pain to the point of total exhaustion. We’ve heard the theory “no pain, no gain,” but is there any truth behind that claim? Do we have to push our muscles to the point of collapse in order to progress? According to new research, maybe not. Researchers from the University of Utah in Salt Lake City looked at the effects of exercise on muscle and had some surprising results.

What causes muscle pain?

Mistakenly we may blame lactic acid buildup for the pain in our muscles that occurs after working out. But contrary to popular belief, lactic acid is not the culprit. It’s actually three other substances that are released during muscle contraction that cause pain and discomfort: lactate, certain acids and adenosine triphosphate (ATP).

The Experiment

Scientists from the University of Utah wanted to know how these substances contribute to muscle fatigue. To do this, they needed the thumbs from a handful of volunteers. Since the thumb contains muscles that are easily accessible and kept still, it was an ideal specimen for the experiment.

Volunteers were asked to hold still while researchers injected each of the three substances into their thumbs separately, and found that no adverse feeling resulted. They then injected all three substances, at a level compared to moderate exercise, and volunteers reported that they felt similar sensations to fatigue, describing their thumbs as feeling puffy, tired and heavy.

As the researchers increased the amount of the three substances they injected, they found that muscle fatigue increased and in some there was slight aching and pain. When they injected the substances at a level compared to "exhausting muscular contractions," volunteers reported extreme soreness and felt like their thumb had finished a difficult workout.

What the findings indicate is that the feeling of fatigue begins when these three substances begin to build up, and they are an indicator of the remaining energy our muscles have to give. The feeling experienced acts as a physiological warning system that lets the body recognize it is reaching its limit. As the three substance levels increase, the sensation of fatigue grows until they becomes so concentrated that they activate a different set of neurons that cause feelings of pain.

Should you work through the pain?

The same researchers conducted another experiment where they gave mild opiates to cyclists to block muscle pain from the brain. They found that the cyclist were able to ride faster than they could before, and felt at ease while riding. Then suddenly without warning, their leg muscles would give out, going limp and requiring assistance for them to get off their bikes. Researches wrote that this type of training is not beneficial in the long run and can lead to muscle damage.

When should you stop?

For most, when we start feeling that pain of muscle fatigue we stop exercising. Those who push through the pain are at risk for injury. It is important to listen to the signals your muscles are giving during exercise. That burn in your muscle is to be expected while exercising vigorously, but pain indicates that something may be going wrong or that the muscles are being pushed too hard. Everybody reacts to muscle strain differently, and each exercise regime should reflect what your body is capable of. Speak with your doctor before starting a new or more intense exercise routine. Above all else, listen to you body. If something is causing you pain, stop and address the problem either with your doctor or personal trainer.

To learn more about diet and exercise:
Exercise Tips & Guidelines for Diabetics
Walking vs. Running: Which Is Really Best?
3 Equipment-Free Exercises to Combat Diabetes