Anyone who has overdone it physically or overdone it in sports knows it: The next day, the muscles pinch, especially with certain movements. They swell, harden and become sensitive to pressure, and you feel stiff. Unaccustomed or heavy use of the muscles causes muscle soreness – a sign of overload.
How does sore muscle develop?
In the past, it was assumed that it was due to hyperacidity in the muscle. Today, however, sports physicians know that it is mainly a matter of many tiny injuries in the microstructures of the muscle. These injuries cause inflammation and small swellings, which in turn lead to the well-known pain.
In addition, muscle tension is increased after overuse and also contributes to causing muscle soreness. Normally, the micro-injuries heal completely and the changes in the muscle regress.
There is no evidence that frequent muscle soreness causes injury. However, loads should be avoided during muscle soreness. If the muscle is stressed during this phase, there is a risk of straining and even tearing larger structures in the muscle. Frequent strains during these phases can also cause irritation in other areas, such as the tendon insertions.
Some sports are particularly “muscle sore”, for example those with extreme running and braking movements such as squash.
When the muscle becomes sore – an outdated thesis
For energy production, the muscle has the aerobic (with oxygen) and anaerobic (without oxygen) metabolic pathways available. Carbohydrates and fats serve as fuels. In the aerobic pathway, these fuels produce water and carbon dioxide (CO
2
), which are exhaled through the lungs. Oxygen is required for this. This pathway can be utilized during moderate exertion such as walking.
During heavy exertion, the body requires more energy, which must be made available quickly. Oxygen transport is overtaxed and the anaerobic metabolic pathway is resorted to. The end product is lactate (salt of lactic acid). The more intense the muscle work, the more lactate is formed. In stress situations, the breakdown of lactate to water and carbon dioxide proceeds more slowly than the formation of lactate in the muscle cells. The result is over-acidification of the muscle.
In the past, it was erroneously assumed that this was the reason for the development of muscle soreness. The hyperacidity hypothesis has been rejected for two main reasons:
- Muscle soreness occurs with a time delay to exercise. By this time, lactate has long been degraded.
- Muscle soreness usually occurs only during high stress of an untrained body. However, lactate is also formed in trained athletes.
