are most often caused by exercising too hard, and generally feel better with time. But if you haven’t exercised recently, sore muscles for “no reason” 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 three days.

Muscle soreness after exercise is to be expected. However, if you haven’t exercised recently and you have sore muscles for no reason, it’s time to visit the doctor to rule out underlying medical conditions.
Read more: How to Reduce Soreness After Lifting Weights
Consider Chronic Fatigue

Chronic fatigue syndrome is a condition that can trigger a group of symptoms, particularly extreme fatigue and weak, tired or 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.
Soreness From Fibromyalgia

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.
Sore Body for No Reason

Even without exercise, unexplained muscle soreness and joint pain 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.
Review Recent Workouts

If you have a sore body for “no reason,” exercise could be responsible for your symptoms. Delayed-onset muscle soreness — or DOMS — typically appears within about 24 to 72 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.
Read more: What Causes Soreness 3 Days After a Leg Workout?
Get Enough Rest

If you are working out regularly, unexplained muscle soreness and joint pain can be a sign of overtraining. The National Strength and Conditioning Association points out that a properly planned exercise routine is an important part of preventing overtraining. Consult a personal trainer to ensure you’ve planned enough rest and recovery into your workout plan.