If you regularly attend the gym or prefer a bit of endurance exercise, it’s highly probable that you’ve heard of the concept of high intensity exercise (HIT) or high intensity intermittent exercise (HIIT) as it is also commonly referred to. The crux of the HIT message is that you can achieve a lot of the same benefits from a shorter, more intense workout compared with a longer more conventional aerobic workout. But what is the limit? How little can you exercise at a high intensity and still reap aerobic and health benefits. This was the question being asked by researchers from Ontario, Canada in their latest study published in the journal PLOS ONE.
To make the findings applicable to your average overweight Jo trying to lose weight, the researchers used 14 overweight/obese men and women (7 each) who shared the basic characteristics shown in the table below.
The subjects performed 18 training session over 6 weeks on a stationary bicycle. Each session started with a 2 minute warm up at low intensity followed by 3 x 20 second all-out sprints, which were interspersed with 2 minutes of active recovery. With a warm down of 3 minutes, each session only took 10 minutes and was performed 3 times per week. This meant subjects did a grand total of 3 minutes of high-intensity exercise and 27 minutes of low intensity exercise per week.
To determine if this tiny amount of exercise was sufficient to induce favourable changes in the subjects health and physical conditioning, they underwent a number of measures. These measures consisted of muscle enzyme activity reflective of endurance adaptations and blood glucose monitoring indicative of blood glucose control and risk for diabetes.
The table below summarises changes in some of the key markers of health and fitness.
While just 3 minutes of high intensity exercise per week was enough to improve measures of aerobic conditioning, power output, fasting insulin and resting systolic blood pressure in both men and women, benefits in terms of blood glucose control were only seen in men. Other similar studies using HIT models have also found women not to exhibit favourable changes in measures of blood glucose control. The authors of this study suggest there may be a sex-specific difference when it comes to the effect of HIT on blood glucose control.
Nonetheless, the findings of this study are particularly fascinating, given the very low total volume and time commitment required to elicit meaningful changes in indices of cardiometabolic health. Previous HIT studies have typically used exercise sessions of 25 minutes 2-3 times per week, however, this is the first study to show similar benefits with just 10 minute sessions. It’s important to highlight however, that subjects in this study were required to do 20-sec ‘all-out’ sprints. Many other HIT studies have subjects exercise at 80-90% of maximum capacity. The authors of the current study believe this may be one of the key reasons the very low amounts of exercise performed in this study were still effective.
So even for the people who argue they have ‘no-time’ for exercise, it’s hard to see how someone could be soo busy so as not to be able to squeeze in just 10 minutes of exercise three times per week.
Gillen JB, et al. Three minutes of all-out intermittent exercise per week increases skeletal muscle oxidative capacity and improves cardiometabolic health. PLOS ONE. 2014;9(11):e111489.