This feature originally appeared in the 15 May 2025 print edition of Cycling Weekly, on sale in newsagents and supermarkets, priced £3.35. You can subscribe through this link here.
When CW’s features editor emailed me one lunchtime, asking if I’d like to investigate FatMax, I almost choked on my pork pie. What exactly was he insinuating? OK, I had to punch a couple of extra holes in my belt over the winter, but surely that didn’t merit such a callous appraisal of my physique. Only after I threatened to involve HR did I realise I’d been hasty. Although FatMax sounds like the street name of a portly American mobster, it in no way pertains to excess blubber. It is, in fact, a training method that is growing ever popular among pro cyclists.
Much has changed in the thinking about long-distance fuelling over the past decade, principally a paradigm shift in top-end carbohydrate intake, the amount our bodies can absorb and use per hour. The more fuel you can shovel, the longer and faster you can ride. That’s why fuelling is low-hanging fruit for coaches and nutritionists. But the research never stops, and it isn’t all about the supply end – the amount of carbs we take on – but also about how our bodies process them.
The carbs we consume on the bike are mostly short-chain sugars, usually glucose and fructose. But the body holds a store of fuel in the form of long-chain glycogen and fat. Even the leanest athletes have some 100,000kcal worth of fat at their disposal – practically enough to complete an entire Tour de France. If we could tap into this fat store at will, we’d never again have to bother with on-bike fuelling; but sadly, it’s not that simple.
When burning energy, the body always draws on a mix of carbohydrate and fat. FatMax refers to the intensity – down to the last watt, or heartbeat per minute – at which you’re burning the most fat possible. Having spent the winter in my shed doing high-intensity efforts that rely almost entirely on glucose, this was an excellent excuse to explore how to make the most of my underexploited fat stores. Switching to FatMax training would, I assumed, be the ideal opportunity to lose some fat.
The entirely painless DEXA scan produced a body fat reading of 17%, which came as a pleasant surprise. Despite tipping the scales at over 90kg, my body composition got the thumbs-up as ‘healthy’. I was starting to like this place – I should come here more often – but now it was time for the main event. Feeling at home aboard a Wattbike Atom, I was confident of doing myself justice in the VO2max test. But then the mask arrived.
With the gas-collecting apparatus sucking at my face like a determined leech, the outlook became less cheery. I was beginning to understand why Darth Vader seems so pissed off all the time. Suppressing panic, I began pedalling and, several wattage increments later, I maxed out, fiercely expelling my lungs into the gas bags – from which Dodd would extrapolate my all-important FatMax figure.
After studying the resulting data, the respiratory exchange ratio (RER) where fat was used at an optimum, corresponded to 205 watts at 120bpm. This is my FatMax, where I’m burning as much fat as possible – and it’s where I would spend the lion’s share of my training for the next two months. The intensity is not just easy, it’s mind-numbingly sedate. So what purpose would all this gentle spinning achieve?
Health over weight loss
“We developed FatMax for one reason,” said Asker Jeukendrup, who was part of the team that invented FatMax training, “and that was just to get a complete picture of someone’s physiology. We did one study early on where we trained patients with fatty livers at FatMax, then compared the effects to interval training. They gained more benefit from FatMax.” What about for someone like me whose liver is (hopefully) not clinically fatty? “Since that study, people have been suggesting FatMax is good for this or that, but we don’t have a huge number of studies.”
Hang on, surely the clue is in the name? Wouldn’t spending more time burning the maximal amount of fat help obliterate the wobbly stuff and improve my tumultuous relationship with the bathroom scales? Not necessarily, according to Javier Gonzales, a professor of nutrition and metabolism at the University of Bath. “There isn’t really much evidence that specifically exercising at FatMax is any better for fat loss or weight loss than other intensities,” Gonzales told me. “It’s true that you’re burning proportionately the most fat, and least carbohydrate, at that intensity, but overall fat loss and weight loss in the long term is more dependent on the total number of calories you’re burning.” In other words, racking up a calorie deficit week after week was the most direct route to shifting excess body fat.
The verdict got worse: by tapping away at 120bpm, I was burning energy at a slower rate and therefore making it harder to accrue a calorie deficit. FatMax was not going to release me from the burden of my buckle-busting midriff any time soon. So how exactly was sitting in this ultra-low zone going to improve my performance on the bike? “The idea, for those fatty liver patients, was that if you train at an intensity where you burn the most fat, you would also automatically train the fat-burning system,” said Jukendrup. More hours at low intensity would mean I’d develop more mitochondria, potentially helping my body use energy more efficiently.
As a health dividend, these sessions would fire up my fat-burning system to make my body less reliant on carbohydrate, increasing my metabolic flexibility. Developing more mitochondria should mean improved endurance and faster recovery. OK, I was sold. First, though, I needed guidance as to the optimum number of FatMax sessions to complete in a week, and the optimum duration for each one. “The longer you go for, the more fat you’ll be burning, and the less carbohydrate you’ll be burning,” explained Gonzales.
The thought of sitting in the shed at 120bpm for hours on end wasn’t a particularly joyous one. Thankfully, spring came a little early this year, so my road bike came out of hibernation and two months of Operation FatMax began. I soon discovered that sitting at my exact FatMax intensity outside was like herding cats. The slightest gradient change altered my heart rate, and my power graph rose and fell erratically. How precise did I really need to be?
“For endurance activities like long, steady cycling or running, your heart rate tends to drift up over time anyway,” said sports scientist and coach Anthony Fletcher, “so a heart rate [target] becomes a moving goal post… I tend to talk about [FatMax] heart rate generally aligning with Zone 2 for most people.” For Fletcher, FatMax is a range rather than a precise figure, and he advises riders to be guided by their perceived exertion at their prescribed FatMax heart rate, cautioning that “for some people, it’s an RPE of six [out of 10], for others a three”. Fletcher’s rationale is that keeping within the right ‘feel’ ballpark makes FatMax training more feasible on the open road.
CW’s Steve Shrubsall undergoes lab analysis to set his FatMax intensity
(Image credit: Future)
Widened FatMax window
After eight weeks of FatMax training, it was time to find out if I had become a more efficient cyclist. My follow-up lab test showed that the heart rate corresponding to maximum fat-burning had remained more or less static at 120bpm. However, the window had widened – up to 136bpm – meaning I had quite a lot more bandwidth to play with. Fletcher advised that, because I was already relatively well trained, I could not expect more than a marginal gain in eight weeks.
As interesting as the experience has been, I remain ambivalent about FatMax training. If its purpose is to improve the health of unfit individuals, why should I incorporate it? Everyone already knows that low-intensity exercise is fundamental for building endurance, and as Fletcher commented, “most of the best cyclists in the world have been doing this stuff for decades”.
For practical ease, can’t we just carry on doing plentiful Zone 2 riding? We may not be oxidising fat with the pinpoint precision of a FatMax heart rate, but, as my follow-up test showed, my window for optimal fat-burning is relatively wide, spanning 120-136bpm. Rather than fixating on my heart rate monitor, I’m content to let my fat-burning range be guided by feel. As for weight loss, well, that’s always going to start and end in the kitchen.
(Image credit: Future)
Feels too easy? Your physiology doesn’t care
Canadian coach Steve Neal (stevenealperformance.com) explains why FatMax training matters – even if its benefits aren’t immediately apparent.
The amount of FatMax training I prescribe depends on an athlete’s level of fitness. A really fit pro might be pushing 280-300 watts at just 65% of their max heart rate. On the other hand, with a beginner, if their FatMax is under 150 watts, that’s too low a training stimulus, so instead I start them with a lot of Zone 3 work – because they’re not yet fit enough to make full use of FatMax training.
The riders I test are always surprised by how low an intensity their FatMax is. But remember, our physiology doesn’t care what we perceive the work to be. If you’re riding at FatMax, the energy is coming predominantly from fat – it’s working. We want to see a rider’s FatMax improving relative to their threshold or VO2max.
In the case of CW’s Steve, his FatMax of 205 watts is just 43% of his five-minute power of 472 watts. I’d want to see it closer to 60-70%. Currently, his workload while burning fat is relatively low. He’ll only improve it by doing more training at low, FatMax intensity – you have to push it up from below, you can’t pull it up from above. This would, however, mean training upwards of 10 hours a week.
As an example, one rider I work with had a FatMax of 175 watts when I started coaching him. A year later, his FatMax was still 175 watts, but his fat utilisation at that wattage was 40% higher. His crossover point, from burning mostly fat to burning mostly carbs, had risen to 215 watts. This meant that when he took part in races of three hours or longer, he was much better because he was sparing carbohydrate. This is why FatMax testing matters.
FatMax in numbers
45-65% – percentage of VO2max corresponding to FatMax intensity in most people (or approximately 55-75% of FTP)
60-70% – heart rate range, as percentage of HR max, in which fat-burning is greatest (broadly aligning with Zone 2)
0.8-1.5g/min – rate at which fat-adapted athletes can oxidise fat, compared to 0.3-0.6g/min in non-adapted people
20-30% – percentage reduction in muscle glycogen usage during submaximal exercise in fat-adapted athletes
100,000 calories – stored in body fat, compared to less than 2,000kcal in glycogen
