Does on need to have a “genetic gift” of speed to be a world –class runner, or is it all due to training? What happens to your heart rate when you take an exercise rate that increases in intensity each minute? What change in your muscles as a result of an endurance-training program that allows you to run as faster speed over longer distance? What fuel -carbohydrate or fat- is most importance when running a marathon? Research in exercise physiology provides answers to these or similar questions.