Working out with a heavy punching bag can build coordination, body strength and endurance in a session that's surprisingly rigorous to anybody who's never done it. However, the forces involved in this kind of training put a lot of impact on some of the smallest bones in your body. If you experience pain after a session on the bags, it might just be sore muscles growing stronger, or it could be the sign of an injury that means you should stop training long enough to heal.
Sore muscles are to be expected after any resistance workout like a session on the heavy bag. It's part of the workout experience and can be mitigated with ibuprofin and increasing your water intake. However, sharp pains in your muscles might indicate a minor pull or strain. You can apply ice to ease the immediate discomfort and take a few days off to let yourself heal.
Finger and Hand Pain
Punching a heavy bag means putting the entire force of your body behind a strike delivered through the small bones of your hands and fingers. With proper technique, your hands will land in a way that can handle this pressure. Without, you hit the bag at an angle that's dangerous to these bones -- so dangerous that a particular kind of hand fracture is called a "boxer's break." If you feel sharp pain in the bones of your hand, stop punching immediately and check with your trainer or doctor. You can help prevent these injuries by wearing hand wraps.
if you punch with your forearm and wrist straight, the force of the impact "rides" your arm up to your elbow, shoulder and torso. A bent wrist can sprain or break your wrist. As with finger and hand pain, sharp pain in the wrist means stopping your workout and getting checked by a professional. Also like finger and hand pain, you can mitigate your risk for this kind of injury by putting on hand wraps for your session on the bag.
Elbow and Shoulder Pain
Much like with your wrists, you can cause pain and injury in the larger joints of your arm if you punch with poor form. Looping, loose punches with your hand away from your center put the impact of your punch in your elbows and shoulders, rather than "riding the wave" to the large muscles of your core. This risks muscle strains and repetitive stress injuries. You can treat minor pain with ice and ibuprofin, but should check with the doctor for chronic discomfort or pain that restricts your ability to move.
Headaches are a surprisingly common complaint for new boxers after a workout on the heavy bag. These headaches come from one of two rookie mistakes: holding your breath and clenching your jaw. To cure either, pay attention to your form while hitting the bag. Exhale sharply with each punch and inhale between strikes to make sure you breathe properly. For a clenched jaw, you can focus on a loose mouth, or put in a mouthpiece to help absorb the pressure.