Many people say that they don’t exercise because they don’t have enough time. If that’s your case, I have great news for you: exercise sessions seem to be shrinking. The traditional method of cardiovascular training (comprised of long periods of continuous, moderate-intensity exercise) is losing ground for a more time-efficient type of workout – the High Intensity Interval Training (HIIT). HIIT is a cyclic workout that alternates bouts of higher-intensity exercise with lower-effort recovery intervals. This is a protocol commonly used to boost the performance of competitive athletes, but recent research shows that it can also improve the health of recreational exercisers. In addition, HIIT can provide the same benefits as continuous aerobic training with fewer sessions.
A growing body of evidence suggests that HIIT could be more effective than continuous training when it comes to developing cardiovascular fitness, increasing fat metabolism and improving blood glucose control. However, HIIT is not for everyone. You should be screened by a doctor before participating in this type of activity in order to rule out any underlying cardiovascular disease. Also, it is important to keep in mind that the exercise session should be terminated immediately if you experience any of the following symptoms: chest discomfort, lightheadedness, severe fatigue, and shortness of breath. Because of its strenuous nature, HIIT should be reserved for more experienced exercisers. Hey, don’t give up just yet. If you are just starting, there are some modifications you can apply to the protocol to make it more suitable and safe. Here is a step-by-step guide to creating your own HIIT program.
1. Choose the exercise mode
As with traditional aerobic training, you must select activities that engage several major muscle groups. Such activities include brisk walking, running, jumping rope, cycling, and rowing. Swimming is only an option if you are a skilled swimmer. Other body-weight exercises such as squats, step-ups, and lunges can also be used.
2. Warm-up
In order to prepare your body for a high-intensity activity, it is essential to perform a proper warm-up. You don’t need a fancy routine; just perform the chosen activity at a slower pace. For example, if you intend to run, start your warm-up with a brisk walk. The warm-up should take from five to 10 minutes.
3. Exercise intensity
As previously explained, this workout is comprised of work bouts followed by active-recovery periods. For the work bouts, your goal is to exercise as hard as you can. At this point, you shouldn’t be able to talk comfortably (if you can, you need to pick up the pace). Of course, high-intensity work cannot be sustained for long periods of time. That’s why you have the recovery intervals in which exercise intensity is reduced considerably. This means that you can manipulate any component of the activity in order to decrease the effort. Reduce your speed, lower the incline of the treadmill, or change the exercise mode (such as switching from jumping rope to marching in place).
4. Work-to-rest ratio
The ratio between exercise bouts and recovery intervals will depend on your fitness level. Beginners are encouraged to use a work-to-rest ratio of 1:2, meaning that for each minute of higher-intensity activity, two minutes of slow-pace exercise should be allowed. Intermediate-level exercisers can use the work-to-rest ratio of 1:1, while advanced exercisers may use the ratio of 2:1. The important thing to have in mind is to listen to your body. If you feel that you need more rest, then take your time. Build up exercise tolerance rather than dive into a strenuous routine without being prepared.
5. Exercise volume
Work bouts can go from as little as 20 seconds to as long as four minutes. The work bouts duration will be determined by your fitness level. I recommend that you start with shorter bouts, and gradually increase the duration as you progress. The total volume of the session will be determined by the number of work bouts and the duration of both work bouts and recovery intervals. Check the following tables to choose the adequate exercise volume for your fitness level. 
6. Cool-down
Before ending your exercise session, it is important to cool-down properly. Perform a low-level aerobic activity such as walking to slowly decrease your heart rate and metabolism, and to prevent the blood from pooling in the veins, which could cause dizziness and fainting. The length of the cool-down should be from five to 10 minutes.
References
Bryant, C., et al, eds. ACE Personal Trainer Manual. The Ultimate Resource for Fitness Professionals. San Diego: American Council on Exercise. 2003.
Dalleck, L. “High-intensity Interval Training for Clinical Populations.” ACE Certified-News. Available at http://www.acefitness.org/certifiednewsarticle/2589/high-intensity-interval-training-for-clinical/?utm_source=Certified%2BNews&utm_medium=email&utm_term=May%2B2012&utm_campaign=Certified%2BNews&CMP=EMC-CertifiedNews_0512. Accessed in May 2012.
Kravitz, L. et al. “HIIT vs. Continuous Endurance Training: Battle of the Aerobic Titans.” IDEA Fitness Journal. February, 2012.