Few races are more important to the women’s peloton than the Tour de France Femmes. Even with just two editions complete – a third begins next Monday – the women’s Tour is already one of the most prestigious races on the calendar, and a race that all of the world’s best riders aim to peak for.
It’s also one of the longest and hardest races on the Women’s WorldTour, demanding a lot from all those who take part. Exactly what those demands look like, however, is a little unclear.
Plenty of research has been done over the years about the energy requirements of elite men’s cycling. It’s known, for example, that the daily energy expenditure of a male Grand Tour rider is somewhere between 3.9 to 5.3 times the rider’s resting metabolic rate – the amount of energy they require for a day of rest. Equivalent data for elite women’s racing, though, is far less common. And that’s a problem.
Riders who don’t know the energy requirements of the races they’re undertaking might be prone to unintentional underfuelling, which might put them at risk. More specifically, there seems to be a relationship between low energy availability, menstrual dysfunction, and decreased bone mineral density. You might have heard of two models that are often used to explain this relationship: the Female Athlete Triad and Relative Energy Deficiency in Sport (RED-S).
Thankfully, progress is being made in this space, including through a recent paper from researchers in the UK, Australia, and the USA. It’s the first case study of its kind to follow a Women’s WorldTour rider at the Tour de France Femmes, analysing their daily food intake, power data, and their energy expenditure.
As it turns out, that rider expended a lot more energy than anyone expected, she was in considerable energy deficit throughout the race, and yet somehow, she still managed to perform at a very high level.
The rider and their race
When it comes to studies featuring elite athletes, researchers don’t tend to reveal which athletes are involved. Sometimes you can work it out – like we did with this study on Mikel Landa’s Giro d’Italia preparation – but most of the time it’s not clear. In this latest study, though, it’s pretty obvious who the rider is. Liv AlUla Jayco rider Georgie Howe isn’t just listed as a co-author on the paper, she also reached out to Escape to let us know that the paper was out, and that it might be of interest to our readers.
The study, headed up by José L. Areta from Liverpool John Moores University in the UK, looks at Howe’s energy input and expenditure throughout the 2023 Tour de France Femmes. Coincidentally, it was at that race that we interviewed Howe for a feature article about her swift rise through the sport, and her time at the 2023 TDFF.
For context, and as listed in the research paper, here are some relevant stats about the former rower at the start of the 2023 TDFF:
Age: 29 years
Weight: 71.5 kg
Body fat percentage: 20.8%
Maximal oxygen uptake: 4.49 litres/minute
Five-minute mean maximal power: 351 watts (4.91 W/kg)
20-minute mean maximal power: 303 W (4.24 W/kg)
It’s noted in the paper that Howe reported having oligomenorrhea – infrequent periods, very common among elite female cyclists – and that she exhibited “clinically low triiodothyronine” – suggesting a decreased metabolic rate and a possible indication of her body in an energy preservation state. Both conditions are markers of low energy availability.
Howe went to the 2023 TDFF riding in support of the team’s GC and sprint leaders, Ane Santesteban and Alex Manly. Speaking to Escape at the race, Howe explained that her role involved “making sure [Santesteban and Manly] have everything they need in terms of nutrition and support within the race as well as just being close to them, checking in on them.” And when the stages got tougher and Howe couldn’t help any more? “It’s time to spin the legs and save for another day.”
Howe also came to the race aiming for a strong individual performance in the stage 8 individual time trial – her strongest discipline. Howe finished 15th that day, en route to 96th overall in a field of 123. Santesteban finished the Tour eighth on GC thanks to the support of Howe and others – a result the team was happy with.
To get a sense of how much energy Howe was taking in and expending throughout the race, she captured a few pieces of data throughout. She’d weigh herself first thing every morning, and she’d provide a urine sample most days of the race (more on that in a moment). Her dietary intake was recorded meal by meal for a total of 8.5 days as well – a day pre-race through to the end of stage 8. Race files from her Garmin Edge 850 (with power data provided by her Shimano Dura-Ace crank-based powermeter) were uploaded to Training Peaks to calculate the intensity of each day’s ride.
Over the course of the race, Howe and her colleagues also used the well-established “doubly labelled water” (DLW) technique to estimate Howe’s total energy expenditure for the 2023 TDFF. This is the most accurate way of measuring someone’s total daily energy expenditure in real-life field conditions, outside the lab. (As Areta told Escape, measuring total energy expenditure in the lab “entails keeping someone inside a tiny room, alone, with specialised sensors for days – quite different from an all-out effort up the Tourmalet with the peloton!”)
In simple terms, DLW involves a test subject ingesting a certain volume of altered (or “labelled”) water in which the hydrogen and oxygen atoms in H2O are replaced with the stable isotopes 2H and 18O.
The decay of these isotopes can be monitored by taking regular urine samples, with the rate of decay providing an accurate estimate of the subject’s energy expenditure over the study period. (If you want to understand more about how this process works, including how isotopic decay is linked with energy expenditure via the production of carbon dioxide, follow the link to read a good primer).
The results
Using the doubly labelled water technique, the researchers arrived at a rather surprising finding. Howe’s total energy expenditure for the 2023 TDFF, averaged out across the entirety of the race, was 7,572 kilocalories/day (31,681 kJ/day). That’s the equivalent of 4.32 times her estimated resting metabolic rate of 1,745 kcal a day – right in line, you might recall, with estimates of energy expenditures at men’s Grand Tours. As we’ll soon see, that energy expenditure was considerably higher than the researchers had hypothesised.
Meanwhile, Howe’s daily average energy intake for stages 1 through 7 – i.e. not including the much-shorter time trial – was 5,246 kcal (21,949 kJ). While that’s more than double the recommended daily intake of 2,400 kcal (10,042 kJ) for an active female adult, it still left Howe with a significant daily average energy deficit of 2,326 kcal (9,731 kJ). That deficit isn’t far off an entire day’s recommended intake for an active adult female.
As a result of such a significant energy deficit, Howe’s weight dropped from 71.5 kg at the start of the race, down to 69 kg by the end. According to the researchers and their analysis of Howe’s urine samples: “[this] is unlikely to be explained solely by dehydration or loss of body water”. Howe just wasn’t fuelling enough.
Here are some other noteworthy observations from Howe’s daily food intake:
- The most energy she consumed in a single day was on stage 4 – the longest stage of the race at 177 km, taking just short of five hours. That day she piled in a total of 6,134 kcal (25,665 kJ) – around 2.5 times the recommended daily intake for an active adult female.
- Stage 4 was her biggest day of carbs too, with over a kilogram ingested: 1,129 g (15.9 g/kg).
- Stage 2 was the day she ate the most fat: a total of 137 g (1.9 g/kg).
- Stage 5 was her biggest protein day, taking in a total of 218 g (3.1 g/kg).
- Her highest fibre intake was on stage 3, with 54 g. Interestingly, as Howe told Escape recently via email, “on stage 3 I had a lot of gastro upset and that was due to too much fibre intake which the research team ascertained from looking at my food diary.”
- Howe’s average daily intake of 5,246 kcal came from roughly 72% carbohydrate, 15% fat, and 13% protein. It’s little surprise that carbohydrates make up the vast bulk here.
You might recall from previous coverage on Escape that there’s a growing focus on high-carbohydrate intakes among pro racers, with some riders taking in more than 100 g of carbohydrate per hour. Howe managed that that milestone on one stage of the race – stage 5 where she achieved 105 g/hour – and her average throughout the seven non-ITT stages was 84 g.
Here are some other observations from the data Howe collected during the race, these ones coming from her power meter:
- The stage in which she had the biggest workload (i.e. power meter-estimated energy expenditure) was stage 4 – a total of 3,442 kJ worth of work (essentially a measure of power output multiplied by time). As noted above, this was the longest stage of the race.
- Howe’s average power during the final-stage ITT was her highest for any day of the race – an average of 297 watts for the 31 minutes (4.30 W/kg) of her time trial. As Areta notes, this effort was “very close to her FTP” – the highest average power she could sustain for an hour – “showing that she can push nearly a maximum effort, even after seven days of hard racing.”
- Her day of highest average power that wasn’t the TT was stage 7, which finished atop the mighty Col du Tourmalet. On that day she averaged 261 W (3.73 W/kg) for the 3 hours 27 minutes of the stage.
- Her highest five-minute power of the race was 388 W on the Tourmalet stage. You might note that this is considerably higher (10.5%) than her previous five-minute PB of 351 W. And it wasn’t just on the Tourmalet stage that she managed a new PB either – Howe also put out 363 W (5.1 W/kg) for five minutes on stage 2.
- Her highest 30-minute power was 317 W (4.53 W/kg) on the Tourmalet stage. While it’s awkward that her best 30-minute power was listed from the race, but her best 20-minute power was listed in the paper’s introduction, it’s worth noting that Howe’s 30 minutes at 317 W was higher than her previous 20-minute PB of 303 W.
- Howe’s best 60-minute effort also came on stage 7, when she put out 293 W (4.19 W/kg) – very nearly as high as her best 20-minute power pre-race.
To summarise the above: the Tour pushed Howe to new limits that she’d hadn’t been capable of reaching before the race. And that’s from a rider who finished well behind the winners on almost every road stage of the race.
Breaking it down
In summing up their most important findings, Areta and co point to Howe’s estimated energy expenditure of 7,572 kcal/day. In their words this “may be the highest individual value to date in a female athlete reported in the scientific literature using the doubly labelled water method, surpassing absolute and relative values reported for female swimmers, runners, and cross-country skiers.”
They expressed some concern at the magnitude of Howe’s energy deficit throughout the race, saying it “appears to be more severe [than among “male athletes of this calibre”] and highlights the need for further systematic research on the energetic demands of female athletes in training and competition.”
That prompts a few questions. How did Howe decide how much she would eat each day? And how did she end up underfuelling by so much? Was that the goal?
“I was guided by the [Liv AlUla] Jayco team nutritionist,” Howe told Escape via email. “They would calculate what I consumed on a given day during and post-race, then prescribe the amounts required for dinner, snacks, and breakfast the following day based on the predicted demands of the stage.”
As Howe explained, the research team hypothesised that her daily energy expenditure would be considerably lower – around 2,000 kcal (8,368 kJ) lower – than what was ultimately reported with the doubly labelled water technique.
“The hypothesis was drawn upon data from my power meter as well as existing research in this space around basal metabolic rate, etc. and any (albeit, small) amount of data existing on female elite endurance athletes,” Howe continued. “This method of measuring energy expenditure has never been used on a female; thus, we were in uncharted territory.
“The nutrition advice I was given from the team was based on the same research and assumptions the hypothesis was drawn from. I was indeed surprised around the energy deficit, but I would not put it down to mal-advice or attempts to intentionally drop body mass during a Grand Tour.”
In their paper, Areta and co suggest that Howe might have been up against a limit of what was possible for her to digest throughout the race; that she wasn’t able to eat enough to keep up with her energy expenditure.
“There was not a moment I wasn’t shovelling food down my throat!” Howe told Escape. “I don’t think I hit a ‘ceiling’ per se, but perhaps changing the types of foods I was consuming could have helped. I was eating a plant-based diet at that stage in my life, so maybe incorporating animal meat would have lifted my raw calorie intake.”
And yet, despite underfuelling by a significant margin each day, Howe still managed to hit several power PBs throughout the race. In Areta’s words: “this is puzzling because models associate chronic energy deficit to negative health consequences but also to negative performance outcomes. It is perhaps the fact that the athlete had a high-carbohydrate diet through the race that, despite such high energy deficiency, [she] did not have a clear negative performance outcome.
“This study highlights how little we know about how energy deficit may affect performance, as it is not clear if her performance would have been better had she fuelled the race as to match the total energy expenditure. We need to understand the energetics of many individuals (not just one) before we can draw strong conclusions.”
Learning from it
Like her co-authors, Howe was surprised just how much she’d been underfuelling by.
“The results were so, so, so far outside what we hypothesised at the beginning that it’s just so stark we need more research in this space,” she explained. “We need more women to be the test subjects and gather more data using this method. Female representation in sport science research is chronically low. I hope this study and the shocking findings spark a ‘call to arms’ for more research in this area of elite female endurance athlete energy availability.
“Selfishly, I felt very fortunate to get this data on myself. It has informed how I go about fuelling and recovery since, for sure. [I’ve learnt] There is no playing catch up when you are already behind in the carb game! I have become more intentional with ensuring I have enough fuel on board before any race or efforts in training. For example, I will start fuelling as soon as I roll out of my house if I have an intense session full of efforts. Those sessions will be around 80 g/hour for the period of the efforts, to practice and train my gut on race nutrition.”
In analysing a study like this, it’s always important to bear in mind the sample size. The findings from Howe’s TDFF are stark, but we can’t extrapolate from one rider’s data to a sweeping statement about the women’s peloton as a whole. The researchers acknowledge as much themselves. “We call for caution in the interpretation of our results and highlight our findings are limited to a single individual, in the context in which data for this case study were collected and subject to the limitations of error of measurement of the methods used,” they write.
And yet, there’s certainly a lesson to be learned here. For female pro cyclists, perhaps this is a good reminder of the need to regularly revisit any assumptions being made about fuelling requirements, particularly if those assumptions are made based on the limited research data that currently exists.
And again, these findings are a reminder of the need for further research in this space, “which will allow [researchers] to tease out the complex interplay between energy balance, health, and physical performance,” Areta and co write. “Such assessments would provide female athletes the opportunity to achieve their best performance, optimise recovery, and maintain normal physiological functions.”
That last point is an important one. Every athlete wants to perform at their best, whenever they can, but sport is only part of the equation. Given what we know about the links between low energy availability and various health concerns, there’s more to be gained from studies like this than racing well at the Tour de France Femmes.
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