If you use heat in this situation it will lead to an increase in bleeding under the skin prolonging the healing process. There are other signs which could indicate more serious injury which may need the attention of a sportsmedicine specialist. If pain or soreness persist beyond a week or two you may want to see a doctor, or if your team has one, a trainer. If the pain is in a joint area, it could indicate a sprain which is a ligament tear. With knees, there is also the risk of torn cartilage.
Cartilage is tissue that provides a cushion between bones and can tear if the joint loses stability.
Swelling and black and blue discoloration also indicate injury to tissue. Limited range of motion or normal movement can also point to injuries of a more serious nature like fractures and more serious sprains. As an athlete your concern is to identify simple sports injuries from those you think may be more serious. Our strength and conditioning coach requires that we keep a training log for off-ice workouts and said that all athletes should keep them during the season. Many athletes have attributed their success to keeping track of all their sport related activities.