Why Are My Muscles Sore if I Did Not Exercise?

Sore, fatigued and achy muscles are most often caused by exercising too hard, and generally feel better with time. But if you haven't exercised recently, sore muscles could be an indicator of an illness or other health condition. See your doctor if you experience muscle soreness with no apparent cause, or pain lasting more than 3 days.

A woman is rubbing her lower back outside. (Image: EpicStockMedia/iStock/Getty Images)

Chronic Fatigue Syndrome

Chronic fatigue syndrome is a condition that can trigger a group of symptoms, particularly extreme fatigue and weak, tired and sore muscles. If you experience muscle pain and soreness in addition to unusual headaches, difficulty sleeping, trouble concentrating and severe exhaustion that lasts for 6 months or longer, chronic fatigue syndrome could be to blame. This condition typically causes muscle soreness in multiple areas of the body. Regular sleep, a healthy diet and regular physical activity can help manage chronic fatigue syndrome.


Fibromyalgia is a syndrome characterized by pain throughout the body and sore muscles, joints and other tissues. Fibromyalgia may also cause mental health issues such as anxiety and depression, in addition to headaches and insomnia. This condition typically causes muscle soreness in the back and neck. The cause is unknown, but it often occurs along with chronic fatigue syndrome. No cure is available for fibromyalgia, but lifestyle changes and regular exercise -- within your body's limits -- can help manage muscle soreness and other symptoms.

Other Health Conditions

Even without exercise, muscle soreness can be caused by an injury or damage to the muscles during the course of daily activities. You may have strained a muscle lifting something heavy or doing vigorous house cleaning or yard work. An infection such as flu or Lyme disease can also trigger muscle pain and soreness in multiple areas of the body. Muscle soreness, pain or cramping may also be caused by an imbalance of important minerals such as calcium or potassium, or even dehydration.

Delayed Onset Muscle Soreness

If muscle soreness sets in a couple of days after a workout, exercise could be responsible for your symptoms. Delayed onset muscle soreness typically appears within about 48 hours after a workout. It can cause mild or very severe muscle pain that can make daily activities difficult. The cause of delayed onset muscle soreness is unknown, but contributing factors may include the breakdown of tissues or inflamed muscles.

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