When Bradley Wiggins made his breakthrough in the 2009 Tour, his 10 kilo weight loss and diet were major topics of conversation. Some estimates had his body fat at 4 per cent which helped him finish fourth overall. He would win the race three years later. Exercise physiologist Stephen Barrett explains what the findings of Chris Froome's physiological data revealed.
The eagerly-awaited physiological testing data from Chris Froome was released in recent days and it makes for some interesting reading.
The common consensus, however, is that even though it answers many of the questions people had about the physical make-up of Froome; many questions are still to be answered.
To take a step back let's quickly look at the three main factors that influence cycling performance.
Former Irish international turned exercise physiologist Stephen Barrett makes sense of Froome's physiological data. The Corkman said the data revealed a lot - but also left some questions unanswered.
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VO2max
In simple terms this is the size of your ‘engine’; or more specifically, the volume of oxygen you can consume while exercising at your maximum capacity.
Froome’s VO2max of 84 ml/kg/min would be what is expected of an elite endurance athlete.
To put that into context, I’m sure many of the top riders around Ireland would have VO2max scores north of 65 ml/kg/min with ‘normal’ peoples VO2max closer to 30 ml/kg/min.
The more oxygen you can consume the more red blood cells you can get to your working muscles.
VO2max, however, is only a piece of the jigsaw. VO2max alone isn’t a very good predictor of performance.
Another key determinant is how efficient you are at putting that oxygen to good use.
Efficiency
The most successful endurance athletes are always the most efficient athletes.
Efficiency is a measure of how much oxygen you need to use over a specified distance or at a given power output.
Two cyclists with the same VO2max but one with better efficiency will travel faster all day long.
I’m sure there are other top cyclists with VO2max figures similar to Froome’s but it is conceivable he is a more efficient rider, as evidenced by the cadence he rides at.
Froome’s efficiency data was not released but with an upcoming scientific paper to be published in the near future, it will likely be outlined in that research.
Threshold Power
Most people will be familiar with their threshold power as the maximum power they can sustain for 1 hour.
This power is normally reported as a percentage of VO2max.
A key trait of all successful endurance athletes is their ability to stay at a very high percentage of VO2max for a sustained period of time.
Froome’s sustainable power of 419w, again, would be well within the norm for top riders.
But probably the most important factor is that this power did not change following his 8kg weight loss.
Think of an F1 car with the same horsepower shedding over 10 per cent of its weight; it is going to go a lot faster!
Getting a Vo2 max test is something many riders get done in the off-season. The test determines how big one's engine is. In the case of Chris Froome, his Vo2 max one of his biggest attributes.
Much of the original speculation was aimed around Froome’s VO2max and his sustainable power numbers.
However, once the data was released and those numbers were recognized as within the ‘norms’ for Tour contenders, much discussion has been centred around Froome’s dramatic weight loss of 8 kilo between tests in 2007 and those carried out earlier this year.
To the normal person, an 8 kilo weight loss over this period of time might not sound like a lot.
But for a pro cyclist where 1 kilo body weight over a 30 minute climb can equal a minute in time; this could be a huge performance gain.
Froome’s weight, along with most cyclists, is always a hot topic of conversation around social media when the Grand Tours are taking place.
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Cast your mind back to 2009 when Bradley Wiggins made his breakthrough in the Tour - his 10 kilo weight loss and diet were major topics of conversation.
Froome’s 2015 Tour weight of 67 kilos wouldn’t have been out of the norm amongst his fellow competitors.
However, because he maintained his threshold power, his power-to-weight ratio was going to be much higher.
Power-to-weight ratio is the formula used to determine your power compared to your weight and is an excellent way of comparing riders of different weights and sizes.
The higher your power-to-weight ratio the faster you should go.
To calculate it all you need to do is divide your power at a given intensity by your bodyweight (kg). The most commonly referenced power-to-weight is at your threshold power.
Increase your power-to-weight ratio three ways
- Increase power output while maintaining your weight.
- Maintain power output while decreasing your weight.
- Increase your power output while decreasing your weight.
Froome took the second option above and did it very effectively.
Froome looked gaunt at the Tour this year and last but it was a key reason for his swashbuckling performances in the mountains.
His power-to-weight at threshold in 2007 was approximately 5.6 w/kg while at the Tour this year it is estimated at 6.3 w/kg.
That is a little over a 12 per cent improvement in his power-to-weight ratio.
Not to draw comparison, but a paper published in the Journal of Applied Physiology in 2005 by Ed Coyle entitled ‘Improved muscular efficiency displayed as Tour de France champion matures’ was quoted as saying about Lance Armstrong;
‘During the months leading up to each of his Tour de France victories, he reduced body weight and body fat by 4-7 kg (i.e., approximately 7 per cent). Therefore, over the 7-yr period, an improvement in muscular efficiency and reduced body fat contributed equally to a remarkable 18 per cent improvement in his steady-state power per kilogram body weight when cycling at a given VO2’
In 2007 Froome’s body fat percentage was reported as 16.9 per cent, which is exceptionally high for a professional cyclist.
I would have body fat measurements from a number of GAA teams using the gold standard DEXA method and would rarely see figures over 15 per cent in the competition phase of the season.
Froome’s 2007 measurements were also taken in July right in the middle of racing season, which is further surprising.
In Grand Tour-ready cyclists you expect to see body fat percentage closer to single digit figures with Bradley Wiggins reportedly having 4 per cent body fat during the 2009 Tour de France.
Bradley Wiggins went from track powerhouse to bag of bones to win the Tour, and was already very lean before he joined Team Sky.
Dropping body fat too low can, however, be detrimental to performance and health.
It can have a negative impact on immune function, ability to recover effectively and can disrupt your sleep.
Finding that ideal body fat range where you can still maintain maximum power output should be a key goal for every competitive cyclist.
To conclude, a lot of the talk is centred on the dramatic weight loss of Froome as the overriding reason for his transformation from an average rider (albeit with a big engine) to almost untouchable in the mountains in 2013 and 2015.
As has been said in the media, this is not a donkey into a racehorse story. But the data released only gives a snapshot of Froome’s physiology in 2007 and in 2015.
The meat of the story is what happened in the interim years to make him what he is today; a much more efficient rider.
The line often thrown out by Team Sky is the aggregation of marginal gains.
I have no doubt this has played a part in Froome’s rise to the top with the optimization of his aerodynamics, nutrition, recovery, pedalling technique, equipment and so on.
This, however, does not answer all the questions we had about Froome’s physiology but it is a start at least.
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