As most anyone whose ever implemented a new workout routine or taken up a new sport knows, muscles get sore when we use them to perform anything beyond everyday activity. Sometimes, muscles get sore from activities we didn’t consider physical – such as painting a room. In other cases, muscles get sore from infection or virus and rarer yet, muscle soreness can be a side effect of certain medications. However, in most cases, muscle soreness is the result of minor, microscopic injury to the muscle tissue due to strenuous physical activity.

During exercise or other activity, muscles stretch and contract. During the stretching phase, especially if the muscle is being stretched beyond its current capacity, tiny tears can occur in the muscle tissue. Along with these tiny tears to the muscle comes minor swelling. It is believed that these minor injuries are what causes the muscle soreness we feel after strenuous physical activity. In the case of routine exercise, the muscles begin to adapt to the repeated use and stretching. As they adapt, they strengthen and heal and the soreness goes away – at least until we stretch them beyond their limit once again.

In the previous example of painting a room, the up and down movement on a ladder or step stool coupled with reaching up and down, may cause the muscles in the arms, legs, and back to stretch beyond normal limits. The result is the same as with exercise, except the muscles will contract back to normal after a day or two because the movements are not regularly repeated.

Muscle soreness is also a common symptom of colds and flu. The cause is most likely associated with minor inflammation of the muscles caused by the virus or bacteria attacking the body’s cells. Additionally, as the body’s cells are busy fighting the infecting virus, muscles and joints may become deprived of the normal flow of blood and fluid levels, causing soreness.

Most of the time when muscles get sore, it is the result of muscle strain and it is not serious. Exercise and muscle strengthening should be introduced and accomplished gradually to avoid more severe or permanent muscle injury, however, do not let muscle soreness deter you from your exercise goals. Other causes of muscle soreness, such as illness or medication side effects, should be discussed with a doctor.