Strech until it starts burning then ease up
It is a diagnosis that is symptom based. There are no lab tests or other tests that can test for it.
Symptoms are usually Chronic muscle pain, moderate to severe fatigue, un-refreshing sleep, sensitivity to smells, light, noise. Headaches. There 18 trigger points that Dr's test to see if patient experiences pain.
Generally you feel like you have the flu but never get better.
Occupational Health Handbook