Here’s another reason to add high intensity training to your workouts

We know the answers to some unusual facts about exercise.

For instance, we know that walking for an extra 10 minutes each day can extend our lives. We also know that contracting our arm muscles as hard as we can for just a few seconds each day can increase their strength by more than 10 per cent. Similarly, just a few four-second rounds of going as hard as you can, while cycling on a bike for example, increases strength and endurance.

A new study, comparing different types of exercise has found they are not all equal for fat burning.Credit:Getty

But the answer to the often-asked question of the best exercise for fat burning, is less clear.

There are multiple studies to suggest weight training boosts fat metabolism. Aerobic exercise and high-intensity interval training (HIIT) do the same. There is little information, however, about which one provides the biggest boost?

A new study, published in the British Journal of Sport’s Medicine, has attempted to find out.

Professor Željko Pedišić, from the Institute for Health and Sport at Victoria University, wanted to understand whether HIIT is more effective at fat burning than aerobic exercise.

So, he and his team analysed the findings of 18 controlled trials comparing HIIT, moderate intensity aerobic exercise, such as jogging, and no exercise for up to 14 weeks. Resistance training was not included as there were not enough studies comparing the effects of HIIT and strength training on fat oxidation.

Participants in the studies ranged from 20 to 63 and did no exercise, aerobic sessions of 40 to 60 minutes or HIIT sessions, such as sprints on the stationary bike or in the swimming pool, of about 20 minutes (including exercise and recovery intervals).

Fat metabolism was significantly greater in those who did any form of exercise for four weeks or more, with HIIT providing the most fat-burning bang for buck.

After 12 weeks of HIIT, each minute of physical activity equated to an additional 0.13 grams of fat burned, the researchers explained. For someone who engages in 150 minutes of physical activity per week, this could lead to approximately 10 kg of additional fat burned in a decade.

Pedišić explained that the possible reason HIIT is “superior” in this sense is its “greater potential… to increase mitochondrial respiratory function and mitochondrial protein synthesis – factors that are associated with improved fat oxidation”.

Dr Filippe Oliveira, a lecturer in the School of Clinical Sciences at Monash University, said although the increase in fat metabolising was minor, HIIT had the added benefit of taking about half the time.

“It was also interesting to note that, in this study, although interval training improves fat oxidation in both ‘normal’ weight and individuals with overweight and obesity, greater improvements were observed in the latter,” said Oliveira, who was not involved in the research.

Though this study did not explore the mechanisms, Pedišić said that previous studies have suggested that higher fat burning during exercise among individuals with obesity may be because of higher resting non-esterified fatty acid concentrations – an important metabolic fuel – and higher intramuscular triglyceride levels.

HIIT is very different for someone who is unfit or overweight compared with someone who is fit or at a healthy weight, so how do we define it?

“HIIT is a type of training that involves repeated bouts of high-intensity effort followed by varied recovery times,” said Oliveira. “The ‘intense workout’ period may range from a few seconds to a few minutes long, and is usually performed between 80 per cent to 95 per cent of a person’s estimated maximal heart rate (the maximum number of times your heart will beat in a minute without overexerting yourself).”

Pedišić added that people who are inactive consult a health professional before starting a HIIT programme: “There are many different types of HIIT workouts to choose from, and an appropriate one may be found even for individuals who never or rarely exercise.”

With about two billion overweight adults around the world and billions more trying to keep their weight within a healthy range, Pedišić said the research is yet another reason to add a little HIIT into your day.

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