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August 15, 2016
Photography by Cor Vos
When you’re both a fan of professional racing and a keen cyclist yourself, it’s only natural to wonder how you stack up against the pros. While tools like Strava have made it easier than ever to see how we compare, it’s very rare that we get a detailed look at the physiology of one of the best riders in the world.
But last week, in the journal Medicine & Science in Sports and Exercise, that’s exactly what we got, with researchers publishing the results from lab tests done last year by Chris Froome.
So just how good is Froome? What does it take to win the Tour de France three times? And how does Froome compare to the average well-trained cyclist? Sports physiologist Dr Stephen Lane investigates.
After a dominant solo win on Stage 10 of the 2015 Tour de France, Chris Froome found himself accused of diplaying ‘supra-physiological’ abilities. Team Sky were left defending their rider’s performance and did so by releasing Froome’s power data from the stage.
This move only sparked further controversy with suggestions the numbers provided by Sky didn’t correlate with Froome’s dominating performance and that, based on the numbers provided, Froome should have been beaten by those who finished well behind him.
The debate continued throughout the 2015 Tour and eventually led to Froome agreeing to undergo laboratory testing, the results of which would be made publicly accessible. A summary of those results was published in Esquire in December 2015 and just last week, the full results of the independent physiological testing, performed at the renowned GSK Human Performance Laboratory, were published in the peer-reviewed journal Medicine & Science in Sports and Exercise.
So what does the paper say? Just how good is Chris Froome?
Controversy aside, the data provided by Chris Froome’s controlled laboratory testing provide some interesting insight into the physical attributes of the now-three-time Tour de France champion.
Froome underwent a range of endurance performance tests at the GSK lab. To begin with, his body composition — fat and muscle mass percentage — was measured using DEXA, a known gold standard for accuracy. Two sub-maximal tests were then undertaken — — one in ambient conditions, another in hot conditions — to measure Froome’s cycling efficiency, lactate threshold, sweat rate and electrolyte loss.
Froome also undertook a maximal graded cycling test to exhaustion to determine his Peak Power Output and corresponding VO2max.
The above is a summary of Froome’s test results. The table uses his laboratory based data and makes comparisons to his reported body mass during competition to represent the values that may have been possible during his optimal physical condition.
On the day of testing Froome weighed in at 70kg. This was 3kg heavier than his self-reported ‘race weight’ of 67kg during the Tour de France. His weight was reported as low as 66kg during the 2015 Criterium du Dauphine, just weeks before the Tour.
At 70kg Froome had 9.5% body fat which is by no means at the extreme of body fat percentages. Male elite endurance athletes typically fall somewhere between 4% and 15%. Long term sustainable ‘healthy’ body fat percentages of a comparable male may range from 5 to 20% but there is large individual variance as to what is sustainable.
When Froome’s body fat percentage is calculated on his optimal reported race weight of 67kg, his percentage is as low as 4.1%. This calculation assumes his hydration status was similar and there were no changes in muscle mass in the weeks after the Tour.
The DEXA scan was done approximately three weeks after the Tour de France and it is assumed that Froome had greatly reduced his training volume since then and turned his focus to recovery. For Froome, 9.5% body fat is most probably a level he can sustain without putting his body under undue stress. This would assist with recovery while still allowing him to maintain his form leading into the 2015 Vuelta a Espana.
The sub-maximal testing undertaken by Chris Froome required him to ride on his own bike connected to an ergometer that controlled the power independent of cadence. The test started at 250 watts and increased at a rate of 25W every four minutes. This test was done twice — once under ambient conditions, and once under hot and humid environmental conditions.
During the sub-maximal testing, blood lactate samples were taken at the end of each stage and each test continued until blood lactate concentrations were greater than 4 mmol/L — typically representative of an athlete’s threshold (the point beyond which the body can’t clear lactate as quickly as it’s being produced).
The data from the sub-maximal testing revealed that Froome reached threshold at approximately 420W under ambient conditions and, even higher, at 430W under hot and humid conditions. This represents a predicted threshold value of 6.1 W/kg (at 70kg during hot and humid conditions) and as high as 6.5 W/kg at his reported optimal race weight. To the everyday athlete, these values appear somewhat ‘superhuman’.
For comparison, a good A grade or Elite athlete may have a respectable VO2max power of approximately 5.8 to 6.2 W/kg which they can maintain for approximately five to eight minutes during maximal effort. Froome is theoretically capable of sustaining this same relative intensity for up to an hour.
A now-famous chart of power-to-weight ratios at different levels of the sport, created by Andy Coggan. At 6.5 W/kg, Froome’s threshold power is off the chart.
Chris Froome’s VO2max and Peak Power Output (PPO) were measured using an incremental ramp test which started at 150W and increased at a rate equivalent to 30W each minute. Froome reached his limit at 525W (7.5 W/kg), yielding a VO2max of 5.91 L/min (84.4 ml/kg/min). This certainly rates Froome as a world class athlete and when his absolute VO2max values are compared to his optimal race weight, he attains an even more impressive value of 89.5 ml/kg/min.
As high as these values appear it is not unheard of to see values as high as 90 ml/kg/min reported for elite endurance athletes. By way of comparison, the below table outlines values that are typically seen across a range of fitness levels.
It is obvious that highly trained athletes train and race more often and also possess far superior physiological values. Less obvious, and more interesting, is the fact there is often a large overlap in physiological capacity between groups.
For example, A ‘well trained’ athlete may possess a very high VO2max but might not be competitive due to the fact that overall performance is a product of more than just one single physiological measure.
Criteria for the classification of trained, well-trained, elite and world class road cyclists. From Jeukendrup, A. E., Craig, N. P., Hawley, J. A. 2000. The bioenergetics of World Class Cycling. J Sci Med Sport.
Another factor that appears to contribute to Froome’s success is his efficiency on the bike. The ‘Gross Efficiency’ (GE) measured during the testing is simply the amount of energy used to produce a given power output.
In general an elite athlete will be more efficient than a lesser-trained athlete. This difference in economy may be attributed to biomechanics (e.g. a more efficient pedalling technique) and also to biochemical processes that are involved in the conversion of carbohydrates and fats into the energy required for muscle contraction and movement.
Froome’s mean GE was 23.3%, relatively high in comparison to other elite athletes. Typical values have been reported to be approximately 22%.
Throughout a Grand Tour, where athletes are riding for between four to six hours a day, energy conservation is a huge contributor to performance. As the Tour progresses, 1% differences in efficiency can result in huge performance benefits. As the authors of the study write, the combination of a high VO2max and high efficiency is a potential factor in Froome’s success:
“The characteristics of a high VO2peak and high gross efficiency are critical to sustaining high power outputs,” they write. “Such traits are a requirement to excel in time trials and uphill stage finishes, two areas where time is usually gained over other stage race competitors.”
With the Tour de France held at the height of the French summer, it’s clear that handling the heat is an important factor if you’re looking to win the race overall. Froome has said previously that he performs well in the heat and the testing supports this.
The authors of the study acknowledge that the setup of the trial was not optimal — with both the ambient and hot tests performed on the same day — but Froome clearly displayed greater efficiency and higher power outputs at threshold during the warmer conditions that at room temperature.
Froome’s body type is also conducive to efficient thermoregulatory control — a high surface area to body mass ratio means he is able to dissipate heat well. Further support of Froome’s capacity to tolerate the heat is his high rate of sweat loss accompanied by moderate concentrations of sodium in his sweat.
In line with Team Sky’s “marginal gains” philosophy, Froome undoubtedly has an individually prescribed fluid and electrolyte intake target during racing, specific to the environmental conditions and his needs.
The results from this recent publication hopefully provide somewhat more reliable insights into the actual physiology of a Tour de France champion, instead of the usual accusations based upon predicted values. Clearly, Chris Froome possesses a variety of physiological attributes that allow him to excel under specific conditions. Or as the study’s authors write:
“Relative values using the reported competition body mass, peak power output and submaximal power at 4 mmol/L blood lactate concentration are the highest values published to date.”
Uniqueness typically attracts controversy and as such his performances will always be scrutinised. And given the sport’s history with doping, it will be a long time before we are ever certain that such performances are achievable without assistance.
However, from a purely sports science perspective, the data provided from Froome’s testing does seem completely plausible and offers unique insight as to how, when an athlete possesses unique physiological attributes, such ‘supra-physiological’ performances may be achieved.
Dr Stephen Lane holds a PhD in Biomedical Sciences (Exercise Science) and is the founder of HPTek which specialises in cycle coaching and sports science consultation. As part of his PhD studies Dr Lane published numerous peer-reviewed journal articles investigating aspects of cycling performance. Dr Lane works with a range of athletes from recreational to professional and was an integral part of Bridie O’Donnell’s successful UCI Hour Record attempt.