Sprinting is a highly effective form of exercise that combines the benefits of cardio training with resistance work. Sprinting is an anaerobic activity -- it forces your body to draw on your stored energy in order to meet its demands. It also triggers a hormonal response that causes the development of muscle mass. For this reason, sprinting can cause significant alterations to body composition, both in terms of body-fat percentage and lean muscle mass.
Shred Your Legs
Unsurprisingly, sprinters have serious muscle development in their legs. You could expect to see substantial development in your quadriceps, hamstrings and glutes from only doing sprints. The muscle in the lower front of the thigh, just above the knee, tends to be the smallest muscle in the upper leg, while the calves remain relatively small. Overall, your legs and buttocks will become very muscular and very defined from sprinting, due to the tremendous exertion of force they must produce with every session.
Get Ripped Abs
If you've ever watched the sprinting during the Olympics, you'll know that sprinters all have highly defined abdominal muscles -- all of them have six-pack abs. This is because sprinting is one of the most effective ab workouts available. All the muscles in your abdominal area are required to be totally engaged for the duration of the sprint in order to keep your torso upright and balanced, while also keeping all your organs safely in place. Sprinting will add significant strength to every abdominal muscle, and provided your body fat is low enough, you will also start to see the coveted six-pack and obliques.
Most sprinters also have very developed upper bodies. In fact, the upper body of a sprinter is often so defined that striation -- or, definition between the muscle fibers -- is visible. While this level of definition requires very low body fat, regular sprinting will allow your back, shoulders, arms and chest to develop a significant amount of muscle mass and become very strong. This is because the arms act as levers during the sprint, balancing the huge force generated by each step and the rotation of the torso. The chest and back provide the upper body stability to stay balanced and in the correct position throughout the sprint.
Train Smarter, Not Harder
Sprinting is a very high intensity activity. Even world-class sprinters don't run sprints every day, so be careful not to overdo it. Including sprints two to three times per week is enough for you to start seeing noticeable changes in your physique. If you want to see serious muscle definition, it's important to reduce your body-fat levels by eating nutritious foods in appropriate amounts for your body, and to rest and recover regularly.