High intensity interval training (HIT): is it a fast track to health?

A New Year 

For many of us the New Year often begins with a much needed health kick and fresh start. This may be a change in diet, a promise to stop our bad habits, or an aim to improve our physical fitness. This new chapter has motivated me to focus on the latter and improve my training regimen, strength and physical fitness.

Exercise can benefit our health and wellbeing in a variety of ways, including:

- Reducing high blood pressure and the risk of heart disease.

- Promoting weight loss and reducing the risk of diabetes.

- Increasing bone density and protecting against osteoporosis.

- Promoting good mental health and helping manage stress, anxiety and depression.

In embarking on this change the consensus among professionals is a shift in fitness towards short but intense workouts, known as high-intensity interval training or HIT. This has encouraged me to question: how does HIT compare to traditional continuous exercise? Is HIT a fast track to health and can less time really equal greater gain?

Current government guidelines

Government guidelines advise a minimum of 75 minutes of vigorous activity or 150 minutes of moderate activity per week. This advice is in line with that of the American College of Sports Medicine (ACSM) (1998), which stated that physical activity lasting less than 10 minutes is insufficient for developing and maintaining fitness in healthy adults.

However, current exercise research has brought about a sea change and the ACSM now state that durations of exercise of less than 10 minutes may result in fitness and health benefits, particularly in sedentary individuals. This is also of interest in the knowledge that 75% of us are not reaching the minimum amount of exercise per week recommended by the government.


Research results

The research claims that short bursts of intense exercise, amounting to only a few minutes a week, can deliver many of the health and fitness benefits of hours of conventional exercise.

At the University of Birmingham Professor Jamie Timmons found that just three minutes of HIT a week for four weeks, produces a significant change in a number of important health indices. The researchers compared 6 weeks of HIT to 20 weeks of traditional endurance training and found the percentage gain in aerobic capacity to be within the exact same range.

Chris Jordan the director of exercise physiology at the Human Performance institute in Florida claims that 7 minute workouts provide many of the fitness benefits of prolonged endurance training but in much less time.

Research at Heriot-Watt University in Edinburgh found that after only two weeks of HIT, sedentary men experienced reductions in both glucose and insulin levels.

The research claims that HIT addresses two of the major health benefits of exercise:

  1.   Insulin sensitivity
  2.   Aerobic capacity



The science

The first major health benefit is in insulin sensitivity. Insulin removes sugar from the blood, it controls fat and when it becomes ineffective diabetes develops.

The second is aerobic fitness. This is the measure of of how good your heart and lungs are at getting oxygen into your body, also known as VO2 max. This measure is a very powerful predictor of future health.

Researchers claim that by improving insulin sensitivity and VO2 max, you will in turn extend your life expectancy.

How does HIT work? Glucose is stored in our muscle as a substance called glycogen. Researchers believe that the intensity of the exercise breaks down stored glycogen in the muscle much more effectively than moderate intensity exercise. During HIT exercise you are also using more muscle groups in the legs and arms and in turn 80% of the body’s muscle cells are activated, compared to 20-40% for walking or moderate intensity exercise.

We are all individual

This research is compelling and encouraging, however what is really important to know is that people respond to exercise in different ways.

Results showed 15% of people made huge strides (so-called “super-responders”) and 20% showed no real improvement at all (“non-responders”). There is no suggestion that the non-responders weren’t exercising properly, it was simply that the exercise they were doing was not making them any aerobically fitter.

These variations are believed to be due to a difference in a small number of genes. A genetic test has been developed to predict who is likely to be a responder, and who is not.

Potential risks

The research tells us that HIT can help improve the health of those with sedentary life styles and poor fitness levels the most. However, for those of us who are inactive or have a chronic health problem such as obesity, type 2 diabetes and cardiovascular disease, it is important to consider the risks that may be associated with vigorous exercise, including:

- Increased risk of heart attack and stroke.

- Increased risk of musculoskeletal injury in the absence of correct preparation.

- Increased risk of overuse injuries or fatigue.

If you have a medical condition and want to try HIT, seek medical advice and professional support first.

However, it is notable that research suggests that the risks are only slightly higher than with continuous exercise. 

Greater adherence?

Currently there is no scientific evidence to support that the short duration of the exercise workout is an acceptable payoff for the temporary discomfort of high intensity exercise. There is a risk that the intensity may cause lack of motivation and reduce confidence and potentially result in cessation of exercise training all together.


Is HIT for you? Should you swap your exercise routine?

There is considerable evidence that HIT is effective. It can be a good starter program for those of us returning to exercise due to the rapid improvements it can offer. Be mindful that this should be supervised so the type of exercise is safe and the load is matched to personal capacity and is progressed at an appropriate rate.

For those of us that are already active HIT will not have such an effect, however if your training is “…all sub-maximal it could improve your insulin sensitivity and promote muscle mass gain.” According to Professor Timmons. So if you are already healthy and active, HIT may be the ideal way to get more out of your training session.


One size does not fit all

At the moment the advice from the government is ‘one size fits all’, in researching this topic it is clear that this is simply not true and instead we need to tailor exercise to the needs of the individual and take a holistic approach. This permeates throughout this discussion in the knowledge that some individuals do not respond to HIT, there are many different types of exercise that will be effective and HIT does not automatically mean greater adherence.

The research results have enabled us to recognize the significance that microbursts of activity, such as sweeping the floor and taking the stairs can have on our health. This may empower people who are currently sedentary and find the prospect of structured exercise daunting. These conclusions emphasize the importance of asking yourself what exercise means to you? Is it fun and enjoyable and are you able to keep it up?