Lifestyle, stress, and lack of sex are all contributing factors.
Lactic acid.
Knots are muscles that are spasmed or contracted relative to the muscle around them. They tend to be localized and can cause pain and stiffness.
Those are tensed or tightened muscles.
It is possible that the knots are either torn muscles or sebaceous cysts. Both should be treated by a doctor or medical professional.
Muscle 'knots' are areas of tension, otherwise known as trigger points within muscles. Treatment is usually massage or stretching excises.
You're either out of shape, or you just gave your muscles a work out.
trigger point therapy
anxiety
Knots in the back of the arm can be caused by a number of conditions such as inflammation or infection. To get rid of these, swing the arms back and forth, as well as do some shoulder circles.
Knots are areas of muscle that are in contraction or spasm. You can get them from overworking a muscle in your back. You can also get them from overstretching a muscle. This is probably the most common cause since so many of us have failing posture and this causes back muscles to be stretched too much. Muscles also need sufficient minerals and water to function well and not create knots.
It is caused by a buildup of lactic acid due to fermentation in the muscles. This is what is described as "the burn" when exercising.
Disorders of the muscles can be caused by a number of other problems other than the muscle itself. Glycogen storage disorders and undifferentiated connective tissue disease can mimic disorders of the muscles.