If an effective fat-burning workout is what you're looking for, we're here to help. The first step is figuring out if your usual workout is the most efficient at helping you reach whatever goals you may have. We’re busy people leading hectic lives, so it makes sense we'd want the most fat-burning bang for our buck. So, we asked various trainers in London, “What are the best fat-burning workouts?” The answers may surprise you.
How the Body Burns Fat
If you’ve ever researched "how to lose fat," then you’ve probably heard of the fat-burning zone. If you haven’t, the claim is basically that 50% to 60% of your max heart rate (to figure yours out, deduct your age from 220); on a spectrum from walking to sprinting, it’s your heart rate when you’re going at a nice jogging pace.
See, for our bodies to effectively burn fat while we are exercising, oxygen needs to be present. “The nuts and bolts are that more intense exercise burns less fat because we need oxygen to burn fat and as exercise intensity increases the anaerobic contribution increases (energy provision without oxygen),” explains James King, lecturer in exercise physiology at Loughborough University.
We know what you’re thinking: This fat-burning zone sounds ace; jog for a bit and burn loads of fat. Of course, it’s not quite that simple. You may use up stored fat on a nice Sunday jog, compared to a fast-paced, heart rate–pumping HIIT, but after the more intense sweat sesh, you will be burning fat for hours afterward. With a jog, once you stop going, the fat burn may halt too. So HIIT is the best? I hear you ask.
Not so fast: There’s actually another form of exercise that’s pretty great for burning fat too. Weight training causes adaptations in the body that make you burn fat every single day (more on that below). Essentially you shouldn’t choose one over the other; in fact, LISS, HIIT, and weight training should all factor into your weekly fat burning workout routines. Here's why.
Fat-Burning Workout #1:
Okay, so when you’re in that HIIT class, you might not be burning much fat. But after is a totally different story: “A HIIT workout can elevate EPOC (excess post-exercise oxygen consumption) to a level which can, depending on how hard you work (it has to reach the anaerobic threshold), mean you are burning fat for up to 24 hours afterward, even longer in some cases,” explains Sophie Everard, Another Space HIIT instructor.
For that exact reason, Third Space, an exclusive London gym, has a class called AfterBurner, allowing you to rack up an oxygen debt that causes you to burn fat after the session. “AfterBurner is a hardcore functional circuit that utilizes the toughest athletic-based movements like box-jump burpees, battle ropes, and sprints that require massive amounts of energy,” explains Luke Barnsley, personal trainer at Third Space.
“The class runs at an extremely high tempo, with very little rest, which forces your body into an anaerobic environment, around 85% of your maximum heart rate,” he continues. “Once there, the class keeps you in that environment for prolonged periods, and your body has no choice but to accrue a massive oxygen debt. You become a fat-burning machine for up to 48 hours afterward.”
So how exactly does EPOC burn fat? “The oxygen debt can be erased; fatty acids in the body are released and utilized as fuel during recovery, but to achieve this, you have to have trained in the anaerobic threshold [around 85% of your] maximal heart rate,” Everard explains.
The trouble with HIIT is that it’s exhausting and puts a lot of strain on the body, which can lead to DOMS, aka delayed onset muscle soreness. “Fatigue kills HIIT,” says Barnsley, which is why he recommends cross-training your HIIT sessions with some LISS on what he describes as an active recovery day. “On these days, you should focus on stretching, mobility drills and steady-state cardio (heart rate below 140 bpm). This will aid your recovery, meaning you’ll be able to go harder in your next HIIT session, and yes, it will help top up the amount of fat burned,” he adds.
Fat-Burning Workout #2:
A favorite with Kayla Itsines, LISS is any cardio that is done at low intensity in a steady state (hence the abbreviation). You can jog, swim, row or cycle, but you should be able to hold a conversation. “You should be working for 30 minutes minimum and at 60% of your maximum heart rate,” explains Simon Stacks, personal trainer at FitMiBody. “The theory is that your body stops using glycogen (today’s food energy) and switches to an older source (stored energy, aka the fat from last week’s pizza),” he adds.
As you will be going for at least 30 minutes, you want to find the type of cardio you enjoy. And since you want your body to tap into old energy stores, King recommends you do your LISS in a fasted state. However, if you’re going to try fasted training (exercise on an empty stomach), then you want to ensure that you refuel with a balanced meal of carbohydrate, protein and some good fats afterward.
So why not just choose LISS as your fat-burning method of choice all the time? The answer is that you still burn some fat calories during HIIT and keep burning them after: “The downside of [LISS] is that with lower intensities the absolute energy expenditure will be less (if the duration is matched), which is what actually matters for weight control, not fat oxidation per se,” says King. In essence, a short, sharp HIIT session is more time-efficient than a longer LISS one.
LISS is, however, a great way to get some fat burning in on your active recovery days. Unless you’re a complete machine, your body just won’t be able to take a daily HIIT session, and if you are hitting those hard-and-fast sessions every day, you may not be working to the optimum, so you won't get the results you crave.
Fat-Burning Workout #3:
Fat burning doesn’t just happen as a result of HIIT or LISS; weight training plays a crucial part in revving up your fat burn too. When I asked Stacks what the best fat-burning workout was, he said this: “It depends on a few factors, but the first one is this: What causes the greatest physiological adaption? In plain English, that means what makes your body go, ‘Oh crap, this is stressing me out; I need to change to deal with it.’”
Weight training does just that: If you are lifting heavy weights to failure (where you can’t lift that dumbbell for another rep), then you are causing micro-tears in the muscle, the muscle then repairs and grows to adapt so that next time you lift that weight your body is better prepared, so “you burn energy during training and during recovery,” says Stacks. “Not only that, but this adaption to your physiology (bigger muscles) has now upped your metabolism.”
The more you lift weights, as long as you are doing a progressive overload plan (working towards lifting heavier weights over a period of time), you will increase your muscle mass, which in turn may speed up your metabolism, meaning you’ll become a more efficient fat- and calorie-burning machine.
Some experts estimate that a pound of muscle burns almost 3 times as many calories as a pound of fat.
If fat loss is your focus, then try factoring in two or three weight-training sessions per week, two or three HIIT and one LISS. Ensure you have one rest day too. It could look like this:
Tuesday: weight training
Friday: weight training
Saturday: rest day
Wiewelhove T, Fernandez-Fernandez J, Raeder C, et al. Acute responses and muscle damage in different high-intensity interval running protocols. J Sports Med Phys Fitness. 2016;56(5):606-615.
Cleveland Clinic. Want to lose weight? Build muscle. Updated August 6, 2020.