Myofascial pain syndromes cause weakness, restriction of motion, acute (sudden) pain, and chronic (long lasting) pain. They can be felt as numbness, burning, tingling or aching. The pain typically varies with physical activity, changes in weather, quality of sleep and emotional stress. Myofascial pain comes from myofascial trigger points that form in muscle tissue and fascia (connective tissue). Trigger points often feel like small nodules in the muscle. More active trigger points are tender and generate referral pain patterns when they are pushed on. They cause varying types of pain that include cramping, burning, aching, numbness and tingling. Less active myofascial trigger points can predispose a person to acute pain attacks and cause: muscle weakness and early fatigue (with no sign of muscle wasting), and restriction of motion, with or without pain (i.e. frozen shoulder, tight hamstrings).