Specificity is the fourth training principle. Though there are many ways to get in shape, if you want to be a better runner you are going to have to run. All training can start out as general training. If you want to develop endurance, you can do swimming, biking or circuit training. Eventually you will have to run. If you want to develop strength, you can start with general exercises, but eventually you will want to do exercises that strengthen the running movement.
Training needs to be specific to the movement pattern, the speed of the event and the strengths and weaknesses of the individual.