An Interview with Rob Zachow, Ph.D
The New York Times recently ran an article on the “Scientific 7-Minute Workout”. Not to be outdone, BusinessWeek published an article on “How To Exercise in Four Minutes”. Why all the attention on high intensity training (HIT)?
First of all, HIT has been around for a long time. In the context of the above articles, the rationale is to get sedentary people to do some sort (any sort) of regular physical activity. The problem that is often encountered is getting people to comply with regular exercise; in other words, to stick with it. One of the more common issues that is raised by those whom are, shall we say, less enthusiastic about exercise, is the time involved and the whole gym scene. With busy lifestyles, the practicality of a couple hours per day spent commuting to and from the fitness club, the actual workout, etc., even 3 days per week falls short. So, if some benefits that are traditionally associated with a 45-60 minute workout can be achieved in a fraction of the time at home, why not.
I don’t imagine we burn a lot of calories in four or seven minutes, do we?
The actual energy expenditure during physical activity involves a few key processes that determine how many “calories are burnt”. In the exercise physiology world this is measured in metabolic equivalents (METs, you may have noticed the METs measurement on certain types of aerobic exercise machinery). These variables include the duration of the physical activity, your body weight, and the ability of your muscles to effectively use the oxygen that you breathe. With this in mind, short duration, high velocity training would not be expected to use the amount of calories as do longer duration sessions of moderate or intense exercise.
If burning calories is not the main goal of HIT, what is?The main goal of HIT is not that of weight loss; but instead, certain metabolic and cardiorespiratory (heart and lung) benefits can be achieved in some people. These can include improved glycemic control (better control of blood sugar), blood lipid profile (more good versus bad cholesterol; with a caveat described below) and cardiorespiratory fitness (exercise tolerance). The metabolic effects have special significance when considering people with insulin resistance and type 2 diabetes mellitus; that is, conditions of abnormally elevated blood sugar, which can be accompanied by an unfavorable blood lipid profile.
For the sake of managing expectations, what are the limitations of HIT?What are some of the risks of HIT?
One fascinating thing is that even a single session of HIT has been shown to improve the above metabolic end-points; but the hard reality is that the benefits of HIT, or any exercise, are short-lived; disappearing after around 48 hours without exercise. Therefore, the key is regular exercise; something like every other day at the least. Another thing to consider is that HIT seems less efficient in affecting some important things that are linked with long duration, regular exercise such as lowering resting heart rate and blood pressure, reducing body fat composition, improving the ratio of HDL (good cholesterol) to total cholesterol, and increasing bone and muscle mass.
Realize that HIT comes in many varieties, but the basic program involves going all out in short bursts of around 30 seconds over a period of several minutes (as described in the cited articles) upwards to 30-45 minutes, depending upon the protocol. This will put strain on the cardiorespiratory and musculoskeletal systems; as with ANY exercise protocol, you should consult your physician if considering HIT.
Let’s take a real life scenario: a person walks one hour a day at 3 miles per hour. This person cuts the time to 30 minutes a day and increases the speed to 4 miles per hour. Is that an example of HIT? If so, do the two approaches produce the same benefit?Do world class athletes use HIT? If so, in which sports?
In general, walking is considered a low- to moderate-intensity activity. Turning-up the speed of walking as described may increase total energy expenditure, and if so increase total calories used but this cannot be determined without actual measurements. Again, the idea of HIT is to use repeated short bursts (maybe 30 seconds) of maximal or very near maximal energy expenditure such that the actual exercise totals something like 4 minutes in a 7 to 30 minute session. At best we can only estimate energy expenditure and metabolic end-points (such as blood sugar and cholesterol) based upon controlled measurements that have been taken in test subjects. In order to quantitate the benefits of one activity versus another in you, certain things would have to be measured under controlled conditions.
There are several published reports of HIT being used by competitive athletes, some examples are sprint and distance runners, swimmers, rowers, and cross country skiers. The exact HIT programs that have been reported are variable, but the central idea is the same. What is apparent is that HIT can be incorporated as an alternate workout style; this variety may help in avoiding the exercise plateau that can be discouraging to even the most avid exercise junkie.In everyday language, what is some of the science behind HIT?
Remember, the documented benefits of HIT are those of improved blood sugar and to some degree promoting favorable blood lipids; with lesser effects on cardiorespiratory function. This actually involves some pretty complicated physiology which applies to exercise in general. To boil it down, consider a couple of important parameters: oxygen and sugar. Muscles need many things to function; two critical components are oxygen and glucose (the sugar when we refer to blood sugar). Long story short, muscles use glucose for metabolic energy, and they obtain that glucose from blood. In order to efficiently use glucose, muscles need oxygen. Some of you may have heard of VO2max, this is your maximal aerobic capacity, quite simply, VO2max is how much of the oxygen that you breath that your muscles uptake when undergoing physical activity. The more efficiently muscles can uptake oxygen from blood, the more effectively they work. The more effectively muscles work, the more glucose they uptake from blood. Thus, working muscle draws glucose from blood and lowers blood sugar. This whole idea of muscle work and improved blood glucose also partially explains the favorable shift in blood lipids that is associated with any regular exercise.In your opinion, have researchers fully explained how HIT benefits the body? Are there still unanswered questions?
We have a clear idea of the benefits, and limitations, of HIT. With constantly evolving biomedical technology, I would be very cautious in presuming that we have fully explained anything to date.
If I can get a good workout in seven minutes with only a floor, a chair, a wall or a simple piece of equipment, what’s the use of going to the gym three times a week or buying exercise books and tapes?
This all depends upon your exercise goals. Based upon what we know, HIT serves to improve some metabolic and cardiac end-points in certain people, so it appears that HIT is an option to get people to undertake regular exercise. However, the effects of HIT on improving aerobic performance, lowering blood pressure, and increasing muscle strength and bone density are questionable.
Finally, is HIT here to stay or is it just another passing exercise fad?
The first published reports of HIT in biomedical journals appeared in the 1970’s, and HIT is still going strong (pun intended). Given the fickle nature of exercise programs, that is some pretty impressive longevity. With what we know, HIT is absolutely better than nothing; however, varied routines which incorporate aerobic and resistance activities are best to obtain the full benefits of exercise.
Rob Zachow, Ph.D. is an Associate Professor, Department of Biochemistry and Molecular Biology/Office of Education at Robert Wood Johnson Medical School. He is the Course Director for the Cardiopulmonary and Renal-Endocrine courses taught to the RWJMS-first year medical students. Dr. Zachow teaches first year cardiology, nephrology, and reproductive endocrinology at RWJMS. Contact: Rob Zachow, Ph.D. firstname.lastname@example.org