When treadmill walking becomes boring or tedious, incline or sprint intervals can add variety and boost the intensity of your workout. Increasing intensity for just a few minutes at regular intervals can help you gain more from your workout, according to MayoClinic.com. Incline cardio involves changing the angle of your treadmill to simulate uphill walking or running, while sprinting involves quick, short bursts of speed. Incline and sprint training both offer significant fitness benefits, but certain risks are involved with both forms of exercise.
Increasing the incline of your treadmill platform is an effective way to boost cardio output while you walk. Treadmill walking at 3 mph and 12 percent incline results in the same change in heart rate as running at 6 mph with no incline, according to Matthew Rhea, director of Human Movement at A.T. Still University in Arizona. The uphill climb -- even when performed at a mild to moderate pace -- provides resistance, which demands increased involvement of the heart and lungs.
Sprinting offers similar cardio benefits, according to a study published in the "American Journal of Physiology — Regulatory, Integrative and Comparative Physiology" in 2008. Researchers at McMaster University in Canada concluded that sprint training improves the structure and function of arteries as effectively as moderate-intensity exercise performed over longer periods.
Building Muscle Mass
Both incline training and sprinting offer significant lower-body muscle-building benefits. By working out at an incline, you stimulate greater muscle activity in your calves, hamstrings, and gluteals than you do while walking flat, according to Rhea. In fact, when you increase incline to more than 15 percent, muscle tissue activation in the legs can exceed 75 percent of maximal isometric contraction.
Unlike slower-paced walking or jogging, sprinting recruits fast-twitch muscle fibers, according to Tom Seabourne, who has a doctorate in exercise science. The result, according to Seabourne, is that brief, high-intensity sprinting builds more muscle mass in the legs than moderate-speed endurance training.
Due to the repetitive nature of treadmill workouts, your muscles and joints are subjected to significant stress, whether you’re working on an incline or performing sprints. Your workout, therefore, involves some risk of injury. People who suffer from equinus, or limited ability to flex the foot upward, often discover that working out on an incline aggravates their condition, according to podiatrist, Dr. Stanley Beekman. Sprinting on the treadmill, which involves increased impact than slower-paced walking, can aggravate various hip, knee and foot conditions.
Both incline cardio and sprinting are high-intensity forms of exercise, which can result in normal levels of discomfort. However, if your workout leaves you feeling short of breath, dizzy, unstable or in pain, lower your intensity or stop. If you suffer from a pre-existing medical condition or are returning to exercise after a break, get clearance from your doctor before introducing incline cardio or sprints into your physical fitness routine. Plan to work out at lower intensity, and build gradually as your fitness level improves. You might find that high-intensity training aggravates a previous injury or puts too much stress on your back or joints, in which case you should opt for more moderate forms of exercise.