Common injuries occur when you are training to lose weight. The stress on the knees or ankles can sometimes cause sprains and strains to the joints. Occasionally there is a tear of a ligament. Not knowing what is wrong is scary and frustrating. The first thing to do is to get a good medical examination of your injured area. Once your injury has been determined, ask your health practitioner what exercise would be allowed for your over all health as well as perhaps helping your injury. Think of exercises like yoga. low impact aerobics and possibly swimming to keep you safe and in the exercise mode while healing from your injury.