High intensity interval training (HIIT) is getting lots of press. For good reason; it works. HIIT involves alternating short intervals of very high intensity with longer intervals of active recover or rest. Training like this (previously reserved for athletes) can get you results in a shorter amount of time. New studies are showing that HIIT can be effective for clinical populations, including those with cardiac disease or metabolic conditions such as diabetes.
This does not mean that those with high-risk conditions should be running to Boot Camps, CrossFit, Tabata, P90X or other such high intensity programs. You need to be prescreened by a physician (he or she should know the specifics about the program you plan to follow) and carefully monitored. Ideally, such a program would be undertaken one on one.
If your only option is a group class, make sure you watch before you participate. In a group class it is easy to be caught up in the high intensity environment. "Workout until you vomit" is the unbelievable mantra of some of the more extreme instructors and participants. Keep in mind that a high intensity interval for you may be a fast walk, even if the rest of the class is sprinting. Resist any pressure to do more than what is appropriate for you. Many seem to believe that pain and sweat are indications of a good workout. Check to see if there is air conditioning. If you are in a high-risk category, exercising in the heat is not a great idea. The instructor should be watching participants and correcting their form. One hundred pushups is not a great achievement (and can cause serious injury) if they are done with poor form.
If your doctor clears you, and you opt to choose HIIT training, you need to build a base layer of fitness first, gradually increasing training about 10% a week. Once you start the HIIT program, do no more than one day a week at first. Two and perhaps three sessions can be gradually added in, but never more than three. This goes for the already fit, your body rebuilds with rest; no one should be doing more than three HIIT workouts a week. You still need to do moderate intensity training another three to five days a week. The benefits of HIIT can be great, but the risks are serious and real. CrossFit instructors joke about “Uncle Rhabdo”, a reference to a potentially life threatening condition rhabdomyolysis, where the break down of muscle (from too intense exercise) can cause kidney damage and possibly death. Train responsively with a good instructor and you can get the benefits without the risks from HIIT.