We all know exercise is good for us – it increases fitness levels, assists with weight loss, reduces blood pressure and decreases our chance of strokes, heart attacks and premature death. Being fit also makes us feel good.
So why are we in the midst of an obesity pandemic? How have we become so out of shape, when the human body is capable of such incredible physical feats?
There are of course many reasons, but one of the most important issues in our society is lack of time. This is the most frequently cited barrier to exercise that I hear from patients, colleagues, friends and myself.
How many times have you planned to do some exercise after work, only to come home after a long and stressful day and put off your workout in favour of the TV or internet?
Public health guidelines suggest that we should be doing 30 minutes of aerobic exercise, 5 times a week. This is a well intentioned but unhelpful statement. Like it or not, this is simply not a realistic option for many people, without drastically changing their habits. If you really want to help people change their behaviour, you have to make it easy.
So what we need is a way of getting fit in a simple, time efficient way. What if there was a way of improving fitness levels doing just 10 minutes of exercise, 3 times a week? I reckon most people could fit that into their schedule.
Such is the promise made by proponents of High Intensity Interval Training or HIIT, and for once it's a method that's backed up by some reasonable science and evidence.
HIIT essentially means repeated bursts of high intensity exercise, at or approaching maximal effort, with short rest periods in between, typically within a training session lasting about 10 minutes. The idea being that it's the intensity of exercise that's more important to developing aerobic fitness, rather than duration.
Of course, this isn't a new approach to training. Similar techniques were used by Roger Bannister when he was training to run the mile in under four minutes, and by distance runner Emil Zatopek preparing for the 1952 Olympic games, when he went on to win gold in the 5000m, 10000m and marathon events. It’s also been known by a variety of other names such as 5BX, Fartlek and Tabata.
What's new however, is the growing body of evidence demonstrating just how little of this high intensity training is required to produce beneficial physiological changes in the cardiovascular, metabolic and skeletal muscle systems.
As a doctor, this raises the interesting prospect of using this approach to benefit the health of a sedentary, time-poor general public, not just to improve performance in elite athletes. And as an anaesthetist, I'm also excited by its potential to improve outcomes in patients having major surgery and to assist in their rehab afterwards.
So what's the evidence for HIIT and how low can you go?A number of studies on HIIT have come from McMaster University in Canada (for example see here and here). They suggest that HIIT regimes can be as beneficial as traditional endurance training in improving exercise performance and other markers of health (VO2 max, blood pressure, insulin sensitivity), despite involving considerably less time commitment.
In one such study, the investigators at McMaster compared a very short HIIT protocol with a traditional endurance protocol. The HIIT regime involved 3 lots of 20 second sprints on a cycle ergometer, within a 10 minute session (including warm up and cool down). The traditional endurance regime consisted of 50 minutes of moderate intensity cycling. The sessions were performed 3 times a week over 12 weeks. Markers of cardio-metabolic health (V02 max, insulin sensitivity, muscle mitochondrial content) improved to the same extent in both groups.
Martin Gibala, Professor of Kinesiology at McMaster and author of a number of studies on HIIT, suggests that the one-minute protocol described above (i.e. 3 x 20s sprints), is likely to be the lowest effective workload that will still produce significant health and fitness benefits.
So how we can practically put HIIT into practice, without access to exercise physiology labs and cycle ergometers or treadmills?
One option is to do High Intensity Circuit Training (HICT); there's no special equipment required here, it can be performed anywhere, using bodyweight as resistance.
Probably the best known example of a HICT regime is that designed by Brett Klika and Chris Jordan, who published this practical article in the American College of Sports Medicine’s Health and Fitness Journal. Their seven-minute workout has spawned a number of apps that guide you through the circuit.
The workout combines both aerobic and resistance training in a series of exercises that takes 7 minutes to complete. The circuit consists of 12 stations, designed to exercise all the major muscle groups and achieve a balance of strength throughout the body. Ideally they should be performed in the following order to allow opposing muscle groups enough time for recovery:
- Jumping Jacks
- Wall sit
- Push ups
- Abdominal crunches
- Step ups
- Triceps dips
- High knees running on the spot
- Push ups with rotation
- Side plank
Does this circuit training approach also work? The bulk of the evidence for the benefits of HIIT compares sprint interval training on stationary bikes with more traditional moderate intensity endurance training. I’m not aware of as many studies that compare high intensity circuit training to more traditional workouts (but here's one). However, provided you're exercising fairly vigorously, there seems no reason why HICT shouldn't provide similar benefits in terms of cardio-respiratory fitness.
So what about using HIIT as a tool to help patients?Firstly, we should bear in mind that many of the studies on HIIT are small, short-term, lab based studies on younger people without significant health problems, so we must be careful not to over extrapolate the findings, no matter how exciting its potential to improve patient health. As always we must weigh the potential risks against the benefits.
Furthermore, a very intensive HIIT regime is clearly not appropriate for people who are significantly overweight, injured or have chronic illnesses. So is there a way HIIT can be applied to these groups to improve their fitness? This is the population that could potentially benefit most, but it would be crucial for them to approach HIIT in a sensible, graded way, and only after consultation with a health professional. In the pre-operative setting it’s likely that an individually prescribed and supervised HIIT programme is the safest approach. Several randomised controlled trials are currently investigating this question.
Interval walking is a possible introductory option for those not suited to harder versions of HIIT. Studies from the Mayo Clinic and Shinshu University in Japan looked at this approach in middle aged, sedentary people. Their regime involved simply alternating 3 minutes of easy walking with 3 minutes of fast, higher intensity walking, in which the subjects were breathing heavily but could still carry out a conversation, for a total duration of around 30 minutes. They found improvements in cardio-respiratory fitness and blood pressure, and that these changes were larger than simply walking at a steady pace.
Of course, HIIT is not going to appeal to everyone, and there will be some people who are put off by the discomfort involved with the more intensive workouts. That's fair enough: exercise needs to be enjoyable if it's going to be adopted in the long term. There are plenty of other options around to help get people moving and improve their fitness. However, I would argue that if you approach HIIT in a progressive and flexible way (i.e. if you incorporate it into your life or preferred exercise) then it can also be fun.
HIIT is by no means the only game in town, but it is incredibly time efficient, and this makes it a potentially useful tool for addressing obesity and other lifestyle diseases that are becoming so prevalent in our society.