Interval Training (HIIT): Part II

In a recent post we looked at the advantages of HIIT (High-Intensity Interval Training) exercise when compared to steady-state training, summarising that it’s safe for most, if not all, individuals to undertake – if prescribed properly.



Thanks to the return of our CPET facility, we’ve been able to hone in on the accuracy of our clients’ homework prescriptions.

We’re going to be talking about HIIT again this week, as the more evidence is published on the subject, the longer the list of health benefits grow.

But while most people undertake cardiovascular training – including HIIT – to improve their overall fitness, it can also reduce high blood pressure (BP), and over time can lead to chronic improvements in BP levels.

 

High Blood Pressure

High blood pressure, also known as hypertension, is defined as any resting blood pressure over 140/90 mmHg.

Not many people realise how common a condition it is, estimated to affect 30-40% of the world’s population.

We have good evidence that steady-state, moderate-intensity exercise can reduce blood pressure both acutely and chronically.

But there’s less certainty around the effect of HIIT in those with higher blood pressure, because of the acute increase in pressure on the cardiovascular system that happens as a result of HIIT training

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That’s what makes the recent findings from a research group in Brazil (Perrier-Melo et al, 2020) so interesting.

They compared the effectiveness of steady-state exercise (SS) and HIIT exercise for reducing blood pressure 45 to 60 minutes post-exercise.

Their study looked at data from 196 people between the ages of 20 and 75 – 61 of whom had hypertension and used blood pressure medication.


They found that performing HIIT on a treadmill or indoor bike reduced blood pressure by 10/5 mmHg and 8/4 mmHg respectively.

In contrast, blood pressure was only reduced by 6/3 mmHg and 5/3 mmHg when completing comparable steady-state exercise.

The most common form of HIIT exercise used in the study consisted of 4 minutes of intense exercise, followed by between 1 and 3 minutes rest.

It’s worth noting there were no adverse events in either exercise group.



The study concluded that, in all subjects, HIIT was more effective at reducing blood pressure post-exercise than steady-state.



 

But why was it more effective?



The researchers have a theory.

They hypothesised that the HIIT was more effective at reducing blood pressure because of a reduction in peripheral vascular difference when compared to steady-state exercise.

In other words, there was less pressure in the limbs preventing blood flow to the muscles, which led to increase the area to which blood was spreading and therefore reduce blood pressure.

Imagine your circulatory system as a series of pipes.

If you’re able to add additional pipes or make the existing pipes wider, there’s more space for the water (or blood, in your body’s case) to travel, decreasing blood pressure.



When we exercise, the release of adrenaline and activity of our muscles signals to the body to increase the width of our blood vessels in the exercising muscles, and distribute the blood to more areas in the body – i.e. increasing pipe width and the numbers of pipes available.

 

What does that mean for you?

Put simply, if you struggle to manage your blood pressure, exercise is an incredibly effective tool for reducing it both acutely and chronically.

And this new Brazilian research indicates that HIIT training is as, if not more, effective – providing us with a more efficient tool with which to combat hypertension.