Want to improve your health and fitness? According to current research regular high-intensity exercise can make a significant difference to your health.
Interval training is an effective way to exercise. Most of us have heard of intervals or repeated, short, sharp bursts of strenuous activity, interspersed with rest periods. Almost all competitive athletes incorporate a session or two of interval training into their weekly workouts to improve their speed and endurance. Below are some suggestions that can help you safely incorporate interval training into your workouts. Please be sure to have your physician’s approval before engaging in any strenuous activity.
How To Interval Train. The best way to interval train is to keep it simple by changing one variable at a time; for example, increasing resistance on the trainer while maintaining speed, or increasing the incline on the treadmill while maintaining speed. It makes no difference to the body which variable changes. Interval training can improve your cardiovascular system (your heart and blood vessels) as well as the production of more cellular proteins for energy production and oxygen utilization. Interval training will also improve insulin sensitivity and blood sugar regulation.
Designing Workouts. 
Here are some variables to consider when creating interval workouts:
Speed. Increasing speed is an obvious way to boost intensity. However, increasing speed too fast & too soon can cause injury and should be carefully used to increase exercise intensity only if you are conditioned and free from musculoskeletal injuries.
Incline. Adding incline is another way to increase intensity outside or on most cardiovascular equipment. A change in incline will affect the mechanics of movement by incorporating additional muscles or increasing output, both of which increase how hard the heart works and what the maximal oxygen consumption is.
Resistance. The greater the resistance, the harder your muscles work to move forwards. Resistance can be manipulated by either increasing the tension on cardiovascular equipment or by adding additional weight.
Relationship to Gravity. One of the most effective ways to interval train is to use body weight against gravity. Incorporating squats or push-ups into a workout will increase your heart rate response.
Impact. Impact is most commonly associated with sustained, high-impact activities like running, but plyometrics (explosive movements such as hopping and jumping) are effective for adding impact moves in a non-sustained manner. Including a plyometrics component can increase the intensity of almost any exercise, but plyometrics calls for the same care that is needed when using speed.
Lower Body Alternating With Upper. A simple way to increase intensity and then recover is to alternate a lower-body exercise like a lunge with an upper-body exercise such as a dumbbell shoulder press. This strategy is particularly effective if you’re not very fit. The lower-body exercises increase heart rate, while the upper-body exercise allows a brief recovery.