HIIT stands for high intensity interval training. It’s the latest buzzword in fitness, and comes in a variety of flavors – boot camp, interval training, cardio HIIT, metabolic burn, strength HIIT, CrossFit® and Tabata, to name a few. What all of these have in common is a structure of bursts of intense exercise followed by short rest breaks or less vigorous activity, for a total of 20 to 30 minutes. HIIT promises to deliver the same results in half the time as traditional training – but is it right for you?
HIIT uses work intervals that involve cardio only, strength only, or a combination of the two. Cardio intervals may use machines (treadmill, exercise bike, rower) or body weight only (jumping jacks, jump rope, run sprints). Strength exercises incorporate free weights, elastic bands, kettlebells, battle ropes, or body weight moves such as squats and lunges.
Pro’s of HIIT workouts:
A typical HIIT workout takes 20 to 30 minutes, versus 60 minutes for traditional training. But there’s a reason for this: HIIT sessions must be shorter than traditional strength or cardio workouts because they are so intense. You must go full-out with maximum effort in order to see any real benefits (see Cons of HIIT below for more on this).
Improved cardiovascular function
Studies have shown that HIIT is more effective than medium intensity training at improving cardiovascular function – in other words, it can strengthen your heart muscle. It also improves insulin usage, and reduces cardiovascular disease risk factors.
While many HIIT classes incorporate weights, push-sleds, battle ropes and lots of other do-dads, these aren’t really necessary. You can easily utilize all kinds of body weight exercises at home to achieve the same HIIT result. Think pushups, burpees, lunges, squats, and jumping rope, for example.
Con’s of HIIT
It’s not for everybody
HIIT training, done properly, is intense. You should have a basic level of fitness before trying HIIT, and take it easy the first few times you participate. If you’re not used to exercising at this level of intensity, you may adversely stress your body and heart.
May cause dizziness
HIIT workouts that alternate between standing and sitting at speed cause your blood pressure to drop very quickly, which can cause dizziness. If this happens, stop and rest until you feel ready to join in again, or simply don’t continue any further with the session.
Muscle soreness and injury
Even though the exercise intervals are brief, because of the high intensity and (typically) heavier than normal weight most HIIT programs push, you’re at a much higher risk of muscle or tendon injury. At the very least, you’ll typically experience a higher degree of delayed onset muscle soreness afterwards.
Also, as you perform the exercises at a high tempo, your form may deteriorate. This is especially common in group HIIT classes, where there’s little to no personalized coaching or form correction.
Less fat-burning, more fat storage?
While HIIT’s high intensity will burn more calories over the same duration of exercise time, the work intervals are performed in an anaerobic (as opposed to aerobic) state. You enter an anaerobic state when your body is unable to take in enough oxygen to allow it to burn fat as fuel (fat requires oxygen to be converted to energy). Instead, the body turns to stored glycogen (a form of blood sugar) to produce energy. So during HIIT, the calories burned will come mostly from stored sugar and much less from fat stores.
In addition, too much high-intensity exercise causes a form of stress on the body that simulates the “fight or flight” response, and the hormone cortisol is produced in excess. When more cortisol is produced than the body can use, it’s stored as fat. See my article here for more about how this happens.
If you don’t follow a steady, progressive training plan when working out with HIIT, you can easily become overtrained – resulting in excessive muscle soreness, extreme fatigue, increased appetite, mood swings, lack of motivation, and difficulty sleeping.
HIIT can be a great addition to your fitness program, but should not be the only form of exercise you do. If you decide to incorporate HIIT in your program, don’t go out too hard too fast. As a general guideline, start with one session per week then build up to two or three per week at most, with a minimum of 48 hours recovery between sessions. Also, include other non-HIIT forms of training within your program, such as bicycling, low intensity cardio, strength training and flexibility. Last, if have any injuries or a history of cardiovascular disease, talk to your doctor before beginning HIIT.