Increasing cardiovascular fitness with High Intensity Interval Training

While there is nothing new about the use of High Intensity Interval Training (HIIT) to improve the performance of elite athletes, could the same principle be applied to someone who is overweight and sedentary?

And indeed, HIIT would be ideal for busy unfit people who often cite a lack of time as the reason for not participating in exercise.

Canadian study

A recent small study under researcher Professor Martin Gibala at McMaster’s University in Ontario, Canada, investigated whether sprint interval training (SIT) was a time efficient strategy to improve insulin sensitivity and other indicators of cardio-metabolic health to the same extent as traditional moderate intensity continuous training (MICT).

In the study, SIT involved 1 minute of intense stationary cycle exercises within a 10-minute time commitment. In contrast, MICT involved 50 minutes of continuous exercise per session. The study went over 12 weeks with sessions three times weekly.

Despite the association between low amounts of physical activity and an increased risk of many chronic diseases, the prevalence of physical inactivity is higher than that of all other modifiable risk factors for cardiovascular disease.

The exercise component

The SIT involved 3×20 second ‘all out’ sprints (~ 500W) interspersed with 2 minutes of cycling at 50W, whereas MICT involved 45 minutes of continuous cycling at ~70% maximal heart rate (~110W). Both protocols involved a 2-minute warm up and a 3 minute cool down.

The major novel finding from the study was that 12 weeks of SIT in previously inactive men im-proved insulin sensitivity, cardio-respiratory fitness and skeletal muscle mitochondrial content to the same extent as MICT. This was despite a five-fold lower exercise volume and training time commitment.

Similarly effective

SIT involved 1 minute of intense intermittent exercise within a time commitment of 10 mins per session whereas MICT consisted of 50 minutes of continuous exercise at moderate pace. There was a similar 19% improvement in V02 peak after 12 weeks of SIT and MICT which compares fa-vourably with the typical change reported after several months of traditional endurance training.

With a minimum time commitment, we can wake up those sleeping mitochondria, lose fat, improve insulin sensitivity and cardiovascular fitness

So, how could these findings be used to give advice to people in everyday life? There are many ways a version of this type of activity could be incorporated into the lives of even the most sedentary people. For example, look out for stairs to climb and ascend as quickly as possible. If cycling, look for steep hills rather than flatter ground. Adding some resistance training may also help to build muscle strength.

Exercise & heart risk

One word of caution: there is always the risk of a major heart event with training whether intense or moderate. A large Norwegian study of people who had already had a heart event were put through high intensity training and moderate intensity exercise in a cardiovascular rehabilitation setting.

Among the 4,846 patients, a total of 175,820 exercise sessions lasting ≈1 hour were recorded, distributed on 129,456 hours of moderate-intensity exercise and 46,364 hours of high-intensity exercise. Overall, the incidences included one cardiac arrest with fatal outcome during moderate-intensity exercise and two non-fatal cardiac arrests during high-intensity exercise.

Check CV health first

The results of this study concluded that the risk of a cardiovascular event is low after both high-intensity exercise and moderate-intensity exercise. Considering the significant cardiovascular adaptations associated with high-intensity exercise, such exercise is worth considering for patients with coronary heart disease as well as those who are healthy but sedentary. However, there should be an appropriate cardiovascular check-up first.

So maybe there is a message here for all of us? With a minimum time commitment, we can wake up those sleeping mitochondria, lose fat, improve insulin sensitivity and cardiovascular fitness. And there are no time excuses about fitting this activity into a busy schedule.

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