It’s best you screw your science head on for this one – getting a grip on the concept of afterburn can be just as taxing as the sweat sessions that claim to deliver it.
However, if you want to know how to burn calories fast stick with us.
EPOC: excess post-exercise oxygen consumption
What we’re talking about, according to the UK’s top fitness hotspots, is excess post-exercise oxygen consumption (EPOC), which occurs when you exercise at an intensity that your body simply can’t sustain for an extended period of time, and triggers the body to continue burning calories far beyond the 60-minute mark.
And while an elevated heart rate and protracted calorie burn have been linked to high-intensity interval training in the past, it’s only now that there are multiple studio classes appearing that promise bigger afterburn gains and calorie-torching for days afterward. Call it pushing yourself out of your comfort zone – hard.
Whereas a standard session might typically get your heart pumping at around 50-70% of its maximum capacity, these latest classes want you to push harder. Why? Because the higher the heart rate, the greater the EPOC – and the calorie-burning bonuses that come with it.
In layman’s terms, push your body to the extreme in one of these sessions and your body draws on its stores of carbohydrates, glycogen and oxygen to keep you going.
‘You haven’t been able to breathe quickly enough to meet the increased physical demand and have forced your body to produce energy anaerobically – without oxygen,’ says Professor Stuart Egginton, chair in exercise science at the University of Leeds. ‘This creates an oxygen debt in the body, which must be repaid at a later point when the body is at rest.’
Calorie burning exercises
To burn calories fast you need a workout designed for that, which is being easier to find. Enter the EPOC classes: Flatline at Gymbox, self-proclaimed as ‘the hardest workout in the world’, which is a 45-minute elimination circuit routine made up of six stations (including an atlas stone lift, weighted burpees and a rope climb) and a rest stop. The risk of elimination hovers over sweaters throughout – if you can’t complete the reps, you’re out.
Third Space’s Afterburner sessions are functional circuits that combine stints sprinting on a treadmill with moves using TRX ropes, kettlebells and battle ropes to up your heart rate – and keep it there – while the aim of Orangetheory Fitness’s signature class is to earn 12 ‘splat’ points in an hour-long session, scoring one point for every one-minute interval you train in your body’s orange performance zone (around 84% of your maximum heart rate).
Then there’s HEAT at gym chain Virgin Active, which stands for high energy athletic training and aims to – in head coach Amanda Lau’s words – set your body on fire with drills targeting agility, speed, power and stamina so that, when you come to rest, it remains hot (bonjour, calorie burn) for a long time afterwards.
But what can these classes actually claim? It comes back to the aforementioned oxygen debt – the repayment of this oxygen, as well as recalibrating the body on a biological level after exercise (say, to expel lactic acid build-up) calls for extra energy.
According to the University of South Australia, initiating EPOC can raise the total number of calories burned from anywhere between 6% and 15% of those expended during the workout itself – so if you burn 650 calories during an afterburn class, you can expect to torch around an extra 100 afterward. ‘In one of our classes, you can burn between 600 and 1,000 calories, and by exercising in what we call the orange zone for 12 minutes out of 60, you can expect to enjoy EPOC for up to 36 hours afterward,’ says Orangetheory Fitness coach Rachel Skinner.
The best calorie burning workout
While pounding your way through the sixteenth mile on a training run can make you feel as if your body’s about to check out, the best way to elicit EPOC is with the highs and lows of circuit training.
Studies have shown a direct relationship between both the intensity and duration of exercise and the degree of EPOC, with Australian research suggesting intense interval sessions could almost double your afterburn calorie numbers than the equivalent steady-state jog.
‘For maximum afterburn, alternate short, intense anaerobic exercises like sprints with lower-intensity rest periods that give your body a chance to recognise you’ve stopped, but not long enough to restock its oxygen stores at that moment. That way, every time you elevate your heart rate, you’ll add to the overall EPOC effect,’ says Firas Iskandarani, master trainer at Gymbox.
‘You might notice that you sweat for hours after you’ve finished exercising, which is your body attempting to keep you cool as your muscles and organs carry out the energy-demanding process of recovery,’ says nutritional biochemist Professor David Cameron-Smith.
What’s key is that, if you intend to jump on the afterburn wagon, you give your body the rest it deserves – and requires – after a max effort workout. ‘Super-intense classes should be complemented with longer, lower-intensity workouts as well as full days off so the body can return to its natural state,’ says Skinner.
Don’t do this, and your body will suffer. ‘If your heart hasn’t been trained to work at a given intensity, there won’t be sufficient blood flow to accommodate it, which could lead to pockets of myocardial damage,’ says Professor Egginton.
Yikes. Plus, ‘the human body is smart – it tends to stop (with cramp, sickness or fatigue) when we try to do something we aren’t physically ready to do,’ adds Iskandarani.
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