Wednesday, 08 May 2013 15:44

HIIT versus Continuous Training

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Let's start off by asking the question "what is HIIT?" As the name implies, HIIT, also known as Interval Training (IT) or Sprint Interval Training (SIT) consists of a set number of high intensity exercises, each immediately followed by periods of recovery. The high intensity exercises can range anywhere from between 5 or 10 seconds to 5 or 10 minutes. Likewise the periods of recovery can range in duration too. HIIT also enables you to mix up the intensities of your high intensity periods as well as your recovery periods. By keeping everything varied during a workout everything remains much more interesting than continuous training (CT).

As you’ll see, HIIT is superior to CT in every way. We’ll now compare the two training methods in the following categories:

  • Motivation
  • Weight Loss
  • Time
  • Improved Fat Burning Capacity


When most people get into fitness, they assume that CT is the only form of aerobic exercise there is, even though there are many things you can do with CT; treadmills, cycling, rowing, skipping, stair climbing, elliptical trainers etc. However CT soon gets boring because it can be rather monotonous since you’re exercising at the same pace for duration of the exercise session. Surveys repeatedly show that boredom with exercise is one of the top reasons people give up. I’m sure you can relate to this. What can be more boring than sitting on a stationery exercise bike for 45 minutes, peddling away at the same speed and intensity for the entire duration? With HIIT, because you are constantly changing the pace, it is much more interesting. Informal discussions with clients show that rather than dreading the thought of an exercise session, they actually look forward to the thought of an HIIT session and all it involves. There is something extremely enjoyable about running on full burners for only a few seconds before having a nice gentle stroll, then going full throttle again. A problem with CT is that the thought of only being ten minutes into your run and having another 30 + minutes left to go at the same pace can be rather demotivating. However with HIIT, knowing that you’re running at this high pace for only a few more seconds before having a nice easy walk for one or two minutes for example can be very motivating and can spur you on indefinitely. Working at high intensities is a lot easier if you know you have a rest coming up round the next corner.

Weight Loss

Studies have indeed shown that when it comes to weight loss HIIT is far superior to CT. In 2011 at the University of Western Ontario, 20 men and women were assigned randomly to an HIIT group or a CT group. In the HIIT group, subjects had to run on a treadmill with 4 to 6 bouts of all out sprints lasting 30 seconds. Each 30 second bout of all out sprinting was separated with recovery periods lasting 4 minutes. The CT group jogged on a treadmill at around 65% of their maximal heart rate for between 30 and 60 minutes. Training sessions for both groups took place 3 times per week for a duration of 6 weeks. What were the results? After the 6 week study, subjects in the CT group lost a total of 5.8% of their fat mass. This is great news! But what about the HIIT group? Subjects in the HIIT group lost a total of 12.4% of their fat mass.

The results speak for themselves that HIIT is clearly superior over CT when it comes to fat or weight loss. Feel free to read through the study yourself! So why is HIIT so superior for weight loss over CT? Well there are two main mechanisms for this. It has long been known in physiology that when you increase the intensity of the exercise; you actually increase the rate of carbohydrate metabolism and therefore decrease the rate of fat metabolism. You’re probably thinking that if you want to lose weight, or more specifically fat then this would run counter to achieving your aims. However, when you increase the exercise intensity, you also increase the total caloric expenditure, in fact the total caloric expenditure increases exponentially. So if you burn a greater percentage of fat calories from lower intensity exercise, the total number of fat calories actually burned off is far lower due to the lower total amount of calories actually used in the activity. Whereas if you increase the intensity; you’ll burn off a lower percentage of fat calories but from a far higher total caloric expenditure. If you think about the logic behind this; a lower percentage of a greater number is far more than a higher percentage of a much lower number.


Look again at the duration of exercise in the 2 subject groups above. What do you spot? When reading this study, you’d think there was some kind of a mistake. In fact for the study to have been fair, both groups really should have had similar exercise durations but this wasn’t the case. In the study, the CT group exercised for an average of 45 minutes per session. Compare and contrast that to the HIIT group that exercised only for an average time of 22.5 minutes per session. You read that correctly; the HIIT group exercised for precisely half the time of the CT group. Yet by the end of the study and the subjects all had their body fat percentages taken again, the HIIT group had lost more than double the fat that the CT group had lost; 5.8% in the CT group and 12.4% in the HIIT group! The study shows without doubt that you can lose more than twice the amount of body fat by performing half the amount of exercise with HIIT over CT. In practical terms, this means you can shorten your HIIT session considerably and still attain superior benefits over and above a much longer and less interesting CT session. Are you beginning to see the benefits of HIIT now? I urge you to read the study [1] for yourself. In fact, what is the number 1 reason why most people claim not to take part in any fitness activities? It is not out of laziness or lack of money, but instead lack of time is cited. By making proper use of HIIT you can attain superior benefits over CT with only a fraction of the time being used. As I mention other studies in this book, please make note of the exercise durations of the two study groups involved as this will push home the above point even further. So we’ve established that your HIIT sessions really don’t need to be that long in order to achieve incredible and even superior benefits over CT. But how much time during the actual week must you put in? How many individual exercise sessions should you take part in in order to see these benefits? Well in the study above, a 12.4% reduction in fat mass was achieved in just three individual sessions per week (for 6 weeks). I’m sure I don’t need to tell you just how incredible this is! However, I can refer you to one study that tested the results of only a single bout of HIIT per week on cardiovascular mortality; cardiovascular disease being the single largest cause of death throughout the entire world. This study was truly huge, monitoring 56,000 men and women over a 16 year period. The results were that for cardiovascular disease prevention, a single weekly HIIT session significantly reduced the risk of death in both men and women. Interestingly, they discovered that increasing either the duration of a single HIIT session or the frequency of weekly HIIT sessions had no additional benefits when it came to prevention of death from cardiovascular disease. This study goes to show that if your goals are not weight loss, but more fitness maintenance and disease prevention, all you really need is a single 22.5 minute session per week in order to achieve this. In reality, who can now cite lack of time as an excuse for not exercising?

Improved Fat Burning Capacity

It is known that the more you exercise the greater fat burning potential your body creates for itself. What I mean by this is that the more you exercise, over time your body becomes more efficient at burning fat no matter if you’re out and about engaging in your daily business or even when you’re sat on the couch watching a movie. Why is this? There are several mechanisms within the body that makes this the case! Increase in Mitochondria The first of those mechanisms is the increase in the number of and the size of the existing mitochondria within the muscle cells. Mitochondria are known as the cells “power houses” as this is where glycogen is oxidised and energy is created. When we exercise, over time the increase in mitochondria and their efficiency enhances the body’s ability to burn fat for us. So how does this increased capacity compare between HIIT and CT? Let’s have a look at another study. At the University of Guelph, Ontario in 2008 the study was intended to observe HIIT and its ability to improve the body’s fat and carbohydrate metabolic capacities in untrained individuals. The subjects took part in 10 x 4 minute bouts of high intensity cycling separated by 2 minute recovery periods. Exercise sessions took place 3 days a week for a duration of 6 weeks. At the end of the study, a resting muscle biopsy was taken and there were found to be increases in citrate synthase (26%), a mitochondrial enzyme and 2 different fat transport proteins (14% & 30%). It was found that while cycling at a steady pace of 60% of their maximal heart rate potential, there was a marked increase in fat and carbohydrate oxidation capabilities. Unfortunately, one limitation of the study was that it did not compare HIIT subjects with CT subjects which would have been interesting. Just to clarify also, the study showed that the marked increase in fat and carbohydrate oxidation capabilities was for CT workouts after the HIIT sessions. This shows that after performing HIIT for a period of time and then returning to CT, your body has become more efficient at burning fat. In another study at the same university in 2006 8 women took part in 10 x 4 bouts of high intensity cycling with two minute recovery periods. The subjects took part in 7 exercise sessions over a two week period. At the end of the study, fat oxidation capabilities had increased by 36%. Yet again unfortunately, there was no CT group to compare results to. You think they would have learned their lessons at this university but the good thing that came out of the study was that you can see incredible increases in fat burning potential after only 7 exercise sessions. This is the power of HIIT! However I will now bring your attention to another study that took place at McMaster University in Ontario in 2006. I’m assuming there must be some kind of rivalry between the Ontario institutions to become the authority in HIIT research. Anyway, 16 men were randomly assigned to either an HIIT group or a CT group. Each group performed 6 training sessions over 14 days on a bike. The HIIT group took part in 4 – 6 x 30 second all out bouts of exercise with 4 minute recovery periods between. The CT group took part in 90 – 120 minute bouts at around 65% of their maximal heart rate. The muscle biopsy samples taken before and after the study showed that there were similar increases in fat and carbohydrate oxidative capacity in both groups. But yet again, do you notice anything strange with the study above? Take another look at the overall exercise durations for both groups because the differences here are massive indeed. The HIIT groups exercise sessions lasted for an average of 22.5 minutes compared to the CT group which lasted for 105 minutes. Over the duration of the study this works out at 2 hours 15 minutes (HIIT) and 10 hours 30 minutes (CT).

There you have it! With only a fraction of exercise duration, HIIT is comparable to CT when it comes to increasing muscle fat and carbohydrate oxidative capacity.

Read 22100 times Last modified on Friday, 24 May 2013 21:24