I was first introduced to the concept of high intensity exercise a few years ago when a friend of mine started me on CrossFit (www.crossfit.com). He was a pretty ripped ex-military type who suffered from a pathological love of physical exertion that created great pleasure with any exercise-induced suffering. I had been exercising since I was a teenager and had tried just about every form of running, lifting, cross training in the book but this was different. CrossFit.com would post a different combination of seemingly random tush-kicking exercises every day. The workouts were usually brief but were designed to push you to your maximum. I distinctly remember lying motionless on my couch after doing my first WOD (workout of the day) for about an hour staring up at the ceiling wondering what the heck just happened to me. What was different about these workouts was that they took me to my limits. I believe that is the most crucial element of any exercise program.When I was doing research for The Weight Loss Counter Revolution book I found a treasure trove of evidence for the importance of all out intensity during exercise. There is a great deal of data showing that the human body responds to a form of exercise called “high intensity interval training” (HIIT) in a way that is very different from regular exercise. HIIT pairs short bursts of ‘all-out’ exercise with more moderate or light exercise in multiple intervals. The Crossfit workout that landed me on the couch involved an even more intense form of training. The following video from the New York Times has a good explanation of HIIT from one of the leading researchers on the subject: http://bcove.me/v93ccth5
You can also check out a report from the BBC:
I explain the evidence in The Weight Loss Counter Revolution book in more detail, but to summarize, HIIT shocks your muscles in a way that causes them to freak out in a way. As an example, a group of subjects did a workout on a bicycle where they sprinted to exhaustion for 30 seconds followed by 2 minutes of low intensity cycling for just six sessions over only two weeks. They were compared to a group that worked out for the same number of days and minutes but at only moderate intensity. The groups had a fitness test done at the beginning and end of the study period. At the start the two groups were equally fit and could maintain the exercise for equal amounts of time. After only two weeks, the HIIT group doubled the amount of time that they could maintain the exercise relative to the control group. Let that sit in for a second. It wasn’t as if the control group was doing nothing, they also were exercising. The HIIT group got twice the results in the same amount of time. They also cut the amount of time needed to complete a 30 km cycling time trial by 10%. The oxidative metabolic capacity of muscle increased by 10-35% in the HIIT group compared to the other group. Remember, this was after just two weeks! There appears to be an exaggerated response of muscle in its adaptation to HIIT.
Another study of the same protocol compared it to 40-60 minutes of cycling at moderate intensity. Subjects performed the prescribed routines five times per week for six weeks. Remember, the protocol involved onlly about 15 minutes of exercise total. So 15 minutes three times per week compared to almost an hour five times per week (which is the current recommendation for all adults). That means that the HIIT group exercised about 1.5 hours per week (15 minutes x five sessions) compared with about 4.5 hours in the comparison group (40-60 minutes x five sessions). If someone were to ask you which group would you expect to have a better outcome, a group that works out 1.5 hours or 4.5 hours, which would you choose? You’d be silly not to pick the group that works out three times as long, right? Well, you would be wrong. In spite of this large difference in exercise time, both protocols had similar adaptive changes in muscle metabolism. There was a similar increase in the enzymes that are responsible for aerobic metabolism and a similar amount of fat burning. The fact that HIIT produced the same metabolic response in much less time is a remarkable testament to its efficiency. The end result is to very build muscle and burn fat in about 1/3 the time. Its no pain, no gain, but the pain is just a few minutes in total. Not bad.
- High Intensity Interval Training VS Continuous Cardio Training – what type of Aerobic exercise is best? (fitburgh.com)
- HIIT High Intensity Interval Training (fitnessknowsnolimits.com)
References:Burgomaster KA, Hughes SC, Heigenhauser GJ, Bradwell SN, Gibala MJ. Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. J Appl Physiol 2005;98:1985-90. Burgomaster K, Howarth K, Phillips S, et al. Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans. Journal of Physiology 2008;586:151-60.