I am a fit 51 year old male, who has been running for the past 6 years. I was jogging gently on a level surface, warming up for a race at the weekend , and suddenly got an intense pain in the back of my calf - very similar pain to cramp . I was hydrated and warm. I could walk, but not run on the affected leg, and didn t start the race. 4 days later my calf feels really stiff, and there is no question of running. What s happened, and what should I do?