HIIT should not be confused with interval training. The distinction is that HIIT involves extremely-high intensity levels (e.g., 85 to 100% HRR) for very short periods (e.g., 10 to 30 seconds) coupled with low-moderate intensity levels (e.g., 50-65% HRR) whereas interval training usually involves moderately-high intense levels (e.g., 65 to 85% HRR) for relatively longer durations (e.g., 30 seconds to 3 minutes) coupled with low-moderate intensity levels (e.g., 50-65% HRR).
Here are the benefits to performing HIIT:
- Burns more body fat due to a greater increase in cellular mitrochondrial formation compared to traditional, longer-duration cardio
- Causes a greater "afterburner" effect in which metabolic rate is elevated for a longer duration (e.g., up to 24 hrs)
- Shorter cardio sessions (e.g., 20 mins) that are less boring
- Improves athletic performance in sports requiring varying intensity levels
- Less adaptation than low-intensity cardio training which means your body does not readily adjust to the intensity levels--this helps to burn more bodyfat
- Causes blood sugar control
- Less likely to cause muscle loss due to more activation of muscle fibers and the relatively short duration of HIIT compared to longer duration cardio
- With regard to aerobic exercise (e.g., biking, stairmaster, etc.), HIIT may increase available cellular protein for mitochondria and ribosomes, effectively slowing if not halting the aging process
- Not for beginners as the technique is very challenging
- Not for lazy people as the level of motivation required must be high since better fat-burning results occur when getting out of your comfort zone
- Not for people with cardiovascular problems
- Can easily cause overtraining (HIIT should only be performed 1-3 days/wk)
- Increases the risk of injury
- Does not necessarily burn more calories than longer, moderate-intensity cardio
- Can dramatically increase stress levels on the heart and muscles
- Not recommended for people with orthopedic problems due to a greater impact on the joints
HIIT training should be performed infrequently due to its high-intensity characteristic. Infrequently means no more than two to three times per week. Performing HIIT any more than three times per week increases the risk of overtraining of which symptoms may include muscle catabolism (read: muscle burning). Generally, HIIT training is a relatively advanced technique due to its high-intensity range and increased risk of injury. When you do HIIT, be sure to do it sparingly. You can perform HIIT while running, cycling, swimming, or stair climbing.
No matter which cardio training you choose to do, the bottom line is that you should burn several hundred calories per session. The best part is that even after you're done exercising, the "afterburner" effect will occur. That is, your metabolic rate will be stimulated to continue to burn much more calories than a sedentary person while resting. How great is that?!! So don't neglect your cardio!
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."