How HIIT sessions could help you age well and keep dementia at bay

HIIT’s benefits are many, she says. You burn more calories in a shorter time, and your body will continue to burn calories even in recovery, owing to a principle called EPOC – excess post-workout oxygen consumption. This can create a calorie deficit, so you’ll lose fat.

Your whole system will benefit from the improved oxygen and blood flow as part of increased cardio capacity; you’ll strengthen, stretch and build muscle – and may even lower your blood sugar and blood pressure.

But there’s something else a six-minute HIIT session could deliver: brain food.

Travis Gibbons is a PhD student at New Zealand’s University of Otago; cardiovascular physiology is his focus, and his thesis is on breathing and the brain in extreme environments.

If anyone knows what’s happening to the body during a short, sharp, hard-hitting, HIIT class it will be him.

He recently led research that showed that short bursts of explosive activity which work up a sweat boost a protein essential for brain formation, learning, and memory: brain-derived neurotrophic factor, or BDNF. It may even protect normal brain functioning as we age.

BDNF, he explains, is produced in the central nervous system primarily. “In simple terms, it is like brain fertiliser,” Gibbons says. “It promotes synapse strengthening, neuron growth and improves cell resilience.

“Overall, it is good for forming memories and overall cognitive function. There is also a good deal of evidence that it plays a positive role in psychiatric and anxiety disorders.”

HIIT, he adds, does two things that low-intensity exercise doesn’t do; it increases the amount of platelets in your blood (and it’s these that store BDNF) and it boosts lactate delivery to the brain. (Lactate is produced by cells as the body turns food into energy; the highest level of production is seen in the muscles).

One of these two things, he says, “is probably responsible for BDNF production”. That doesn’t mean, he says, that long-duration, lower-intensity exercise bears no value, because clearly it does.

It is beneficial for improving and increasing overall aerobic fitness, for weight management, for muscle building, for metabolic health, and it increases brain blood flow, Gibbons says.

All of these benefits probably support brain health as well, he adds, just in a different way. He is a long-distance runner – and prefers it to high-intensity workouts, he says.

If, like Gibbons, you’re averse to HIIT, consider that six minutes – the amount of time to start seeing benefits – isn’t that long. And you don’t have to do it that often – certainly not daily.

As Trang says, “Everybody is different, has a different tolerance and level of fitness, but three times a week is plenty. Too much is definitely not good, as it leads to stress and fatigue, and means there’s not enough time for muscle recovery between sessions.”

In Gibbons’ study, the HIIT programme was devised as 40 seconds of high-intensity exercise followed by 20 seconds of rest. This was repeated six times. “The intensity should be high enough that you need to rest intermittently.”

An HIIT session, says Trang, needs some kind of structure, which may be following Gibbons’ 40-20 ratio, or having, say “45 seconds of work, 15 of rest”.

Try “explosive” exercises that increase your heart rate: high knees, sprinting, jumping jacks and squat jumps. Make sure you’re doing a variety of exercises, she adds, “to ensure all the muscle groups are being worked and to make the workout less repetitive” – ie. boring.

What’s happening in your brain, Gibbons believes, is that as you progress through the six minutes, “lactate spills into your blood and starts to accumulate. The brain sucks this up and uses it as fuel. The brain typically runs on 99 per cent glucose, so this – using lactate as fuel – will be very different for your brain.”

It is this shift, he says, that appears to stimulate the production of BDNF in the brain, which has been associated with short-term improvements in cognition and has a cerebral anti-ageing effect.

“Shortly after, your brain and muscles will consume all the lactate and you’ll be back to normal.” If you do this long-term, your brain becomes more flexible metabolically; it gets better at using other fuels, he says.

“Long-term this might provide resilience to cognitive decline, since brain glucose metabolism declines with ageing,” he says. And it’s in ageing that we grow more mindful of our cognition.

As Gibbons says, not many 70-year-olds are doing HIIT sessions – which is why, he says, “engaging in intense physical activity throughout the ageing process may delay the onset of symptomatic neurodegeneration long enough that it never actually manifests”.

By the time you hit 70, and may no longer be able to do high-intensity exercise, your brain may have aged at a slower rate.

In other words, your HIIT classes might have taught your brain to run efficiently on an alternative, sustaining fuel when you’re old.