John Basedow: If an injury has kept you from physical activity, your body is in for a rude awakening once you hit the gym. In the case of isolated injuries, exercise can be beneficial for the rest of your body, but always check with the doctor before working out while healing.
Having one injury is not an exercise deal breaker. Simply isolate the area that is healing and figure out which exercises you can complete in comfort. Gently, test your body to see what range of motion you're physically capable of. Visit a physical therapist if you're unsure about the exercises that could help with your recovery.
With an arm, a leg, or even your back out, the easiest way to continue exercising is to complete your regular fitness activities, but at a slower pace. This will keep the rest of your muscles from atrophying while you heal and keep those sneaky injuries pounds from padding your waistline. Complete more reps on limbs that aren't injured to get a better workout.
If at any time you feel pain, stop. While recuperating, no pain, no gain should not be your mantra. It's better to work up slowly to your regular exercise level than injure yourself by trying too much too soon.
Remember, there is no one universal trick for exercises while recuperating from an injury. Always err on the side of caution and do what you can when you can.
By the time you're ready to hit the gym at full force, you will have a lot less to catch up on.