A HIIT workout can be tricky to define because, at its core, it just means a string of exercises that gets your heart racing, providing a cardio boost to what would otherwise be a serviceable, but less kinetic workout. As Lucie Cowan, a UK-based physical trainer from Third Space, puts it: “HIIT or High-intensity interval training, simply means a workout that mixes periods of hard or all-out effort with shorter rest periods. It has been proven to be an extremely effective and time-efficient form of training.”
But there are some caveats for how to optimize it. “You’ll only reap the benefits if you push yourself out of your comfort zone,” she adds. “As exercise intervals must be performed at an intensity of at least 80 per cent of your max heart rate.”
What are the benefits?
A recent meta analysis of studies into HIIT found it reduced both total abdominal and visceral fat mass. What’s more, because you’re working hard for an intense burst, 20 minutes is more than enough to reap the benefits. “HIIT is not only incredibly time efficient, but can be an absolute game changer for your physique and also your tolerance for and recovery from fatigue,” says Arby Keheli, a strength and conditioning coach.
It can also help you live longer. Intensive movement like HIIT, physical trainer Monty Simmons says, is proven to enhance your body’s mitochondrial quality (that is, how well your body performs the cellular stuff that keeps us alive). “This is not unique to HIIT,” says Simmons, “because general cardio does this too, but the intensity is a strong driver.” HIIT boosts longevity by driving “a higher VO2 max which is strongly linked to better metabolism and cardiovascular health and improved glucose uptake, which is essential to how well your muscles absorb and store carbohydrates.”
Can anyone hit up a HIIT class?
Yes, and no. The full-impact stuff really puts your knees to the test, so if yours aren’t up to it, you’re better off trying a lower impact alternative or passing on HIIT exercises altogether. “High-intensity, high-impact movements magnify the load on joints that are already sensitized,” says Simmons. “And moving very vigorously with high volume can flare them up and leave you feeling beat up.”
While exercise is hailed as a wonderful antidote to stress, you need to tread carefully when it comes to practicing HIIT. “If you’re someone who is already chronically stressed, not sleeping much, or going into burnout, HIIT spikes adrenaline and cortisol, which can add more stress on top of an already stressed endocrine and nervous system,” Simmons says. If this is you, you’re better off sticking with lower intensity exercises such as steady cardio or pilates.