The problem with active recovery from a sports related injury is getting out there and using your body without causing further aggravation to the initial injury itself. Even if you have incurred a shoulder injury, the jolting action of simple running can aggravate and joint injury to the extent that it inhibits recovery. Lower body injuries are inherently worse. Walk on a leg injury and you are automatically putting the injured area under a huge amount of stress, which will slow the course of recovery. Even when we use walking aides such as crutches we are putting unnatural strain on the shoulders and wrists, which can lead to further complications (your leg may get better, but you'll end up with a strained wrist). A broken right ankle when I was younger left me with shin splints on the other leg, caused by hopping here and there!
One of the keys to speedy recovery when you have suffered a major sporting injury is impact free exercise to re-train and re-condition your muscles and your cardiovascular system. If you have traumatised a major joint in some way, through a shoulder dislocation or a knee injury for example, the supportive muscles surrounding the joint will have lost condition whilst you were immobile. These muscles need gradually re-training with low (or no-) impact exercise and/or light weights. Not to mention the ligaments and tendons around the joint area, if they have been damaged they require very careful rehabilitation as they have a poor blood supply compared to the muscles and therefore do not heal as quickly.
Low Impact Exercises
The first, and probably most popular method for post injury rehabilitation because of it's no-impact nature, is swimming. Due to the supportive nature of water, the body's joints need support no body weight whilst you are floating in water and this eliminates the stress which they undergo in everyday life. This provides an excellent opportunity for re-conditioning of the muscles rendered immobile by the injury, both around the affected area, and in other parts of the body. However, it is not only your musculature which loses its condition as the result of injury. Depending upon how long you are immobile, your general cardiovascular fitness will start to deteriorate (this will start to take place after around 3 weeks of inactivity). Swimming also solves this problem. As well as being a very good form of exercise for your musculature, it is also extremely good for cardiovascular conditioning and is equally as effective at burning fats and carbohydrate as land exercise.
Again a low impact exercise which, although it may not be ideal for the upper body (unless you have a cycle with moving handlebars) is extremely good for the legs and cardiovascular fitness. Another benefit of cycling, which would be felt by those who have suffered with knee injuries, is that the natural action of cycling regulates the motion of your knee into a very linear form. This is particularly beneficial if you have suffered an injury that would render the knee joint unstable; it allows effective rehabilitation without putting undue stress on the ligaments surrounding the joint itself.
Often overlooked as a low impact method of exercise, rowing is becoming increasingly popular for exercise in general. It is a very good form of exercise for both the musculature and the cardiovascular system. Engaging all major muscle groups (Stomach, legs, shoulders, back, arms) it really is an extremely effective all round workout. The fact that it does use the whole body and the fact that it is low impact makes it a good all round fitness tool in general and, of course it also has a very good effect upon cardiovascular fitness.
Whatever form of exercise you are using for rehabilitation purposes, make sure that you ease yourself back into your routine gradually. Don't just expect to pick up exactly where you left off, or you'll end up with another injury!