If you're training to run your first long-distance race, for example, a marathon, then putting in the miles is one of the key aspects of training. You'll be putting your legs under a lot of stress, which can lead to tears, tight muscles and problems throughout your body. To avoid this, you will need to have suitable warm-up and cool-down routines, supplemented by a good stretching regime and in some cases, if you're injured, suitable exercise physio treatment.