The short answer to the question is: Yes. Although serious injuries may require surgery and other treatment, and definitely some rest and physiotherapy to ensure full recovery, other aches and pains can be aided with magnetic bracelets or magnetic sports supports.
It is important to stress that playing through a sports injury, and therefore through pain, can decrease the chances of a full recovery. This is not where the brilliance of magnets works best.
The best way to explain when a magnetic bracelet can help you play pain-free is to give you an example. You may be a tennis player that suffers chronic pain in your wrist. This is not a result of a traumatic injury; but is typically a result of repetitive strain on this joint. Playing through this pain is possible but it makes you cautious on certain shots and certainly reduces your power through the racket head. In this situation, a magnetic bracelet could help you play your sport pain-free. With the increased blood flow and the impact of negative ions, you will be more confident to go for whatever shot works to beat your opponent.
Another example could be the gymnast where continual dismounts from an early age cause chronic pain in the knees. As the gymnast grows older and moves away from the gym mat, they may wish to take up other sports but are dissuaded by the discomfort in their knees. Not only would magnetic knee supports offer the traditional joint support of a brace, but it will also work to relieve the pain by increasing blood flow around the affected area.
The closer the magnetic support is to the area of pain, the more effective it will be. For centuries, healers have used such magnetic products to help relieve the symptoms of such conditions as arthritis. It is hard to argue with so much history. Therefore, trying magnetic support to aid pain-free sports play seems a no-brainer.