How do you treat an extensive briuse on my thigh.

Fill a large Zip-lock type plastic bag with ice cubes, or get a frozen ice block for a small cooler, wrap it in a cloth, and apply it to the bruise ASAP. Hold it there for 10-20 minutes (you can take it off for a bit if it feels uncomfortably cold). This will reduce the swelling, internal bleeding, pain and discoloration. Repeat as needed to treat discomfort for the first day. After that, you may find a warm compress (hot water bottle) will reduce the stiffness of the muscle. Eat extra salad and protein for the next week to speed the healing process, and do gentle range-of-motion exercises to keep the muscle limber. Back off on running if it hurts; that's a signal that the muscle isn't ready to run yet.