Stretch cramp

When I awake in bed I stretch, often with a yawn. It's involuntary, you probably do it too, and normally it's a healthy thing. However, for me, it usually results in a cramp, and a feeling of damage to my muscles. If my legs are curled, it hurts the thighs. If they're straight, it hurts the calves. I conjecture that this is the major way my leg muscles deteriorate. I don't dwell on the negative, but I imagine that if some day I am unable to get out of bed and stand up, this will be the reason. I don't know if there are drugs which can inhibit yawning and stretching, but you'd have to think that they'd be awfully nasty compounds that you wouldn't want to take.