Can weight loss explain Chris Froome’s rise through the ranks?

Chris Froome

Exercise physiologist Dr Jeroen Swart, the man responsible for administering Chris Froome’s much-talked-about physiological testing, suggests that Froome’s weight-loss is one of the most likely reasons for the rider’s rise to the top level of the sport.

Now, in a piece on his Veloclinic website, sports physician Mike Puchowicz has examined the contribution Froome’s weight loss likely played in his improvement.

Here’s an excerpt:

”Jeroen Swart has put forward a hypothesis that weight loss is the most likely dominant mechanism explaining Chris Froome’s transformation in grand tours. Supporting this theory Froome had a high documented VO2 of 6.07 L/min in 2007 and a relatively high weight of 75.6 kg. Additionally, Froome showed only a modest loss of VO2 to 5.9 L/min with a concurrent weight loss of 4.8 kg down to 70.8 kg (pre-dehydration weight) at the GSK testing lab in 2015. The weight loss mechanism is appealing for its simplicity and that the weight loss is outwardly apparent in photographs of Froome over time.

In order to test this hypothesis, one can check for a dose response curve consistent with the proposed weight loss mechanism. This approach is necessary in the absence of a good cross over control condition (ie having Froome gain weight and race subsequent grand tours to see if performance drops back to the previous levels). Causation is supported if the correlation shows a dose response consistent with the mechanism. From his interview with Kimage, Froome puts his weight at 70-71 kg with Barloworld, 69 kg during his first year with Sky, and 67 kg in 2011 on. What we see in the grand tour performance is 83rd and 34th place finishes at the 70-71 kg weight, a disqualification at 69 kg for holding on to a vehicle during a climb, and then a series of podium finishes at 67 kg. I would argue that this limited data suggests a level change rather than dose response predicted by Swart’s hypothesis as well as an effect greater than would be expected from a weight change mechanism alone.

Another way to assess for causation of the weight loss mechanism is to the test it across a different condition where there should be little to no effect. Since weight has a relatively small effect on CdA [drag area], and Froome’s VO2 dropped with weight, Swart’s hypothesis predicts that Froome’s TT performance should have not improved or worsened with the weight loss if it was the dominant factor. Instead, just like climbing results, Froome’s TT results in grand tours also increased by a large level change 33, 16, 34, 32, 138, and 39th prior to 2011 Vuelta and 2, 11, 2, 2, 3, 2, 1st etc from 2011 Vuelta on.

Since, the improvement in grand tour climbing performance is far greater than the mathematically modeled effect of the weight loss, and the large level change in climbing performance trends with the large level change in grand tour TT performance which should be relatively independent of the weight change mechanism, it is fairly safe to reject the weight loss mechanism as the dominant factor in Chris Froome’s performance change.”


  1. Dr. Michael Puchowicz has a medical doctorate from Vanderbilt, is a noted specialist in Sports medicine, and is, according to Outside, “one of the foremost antidoping experts”. He is eminently qualified to give forth on whether sporting data fits a weight-loss mechanism model (cited as the sole conclusion by the original researcher) or in fact, much better fits a dose-response curve. His acknowledged credentials give him the authority and the scientific rigor to know how to apply such a curve and to do so, credibly.

    You, presumably, have no such credentials, and therefore no credibility at all in the matter.

    Therefore, no-one will be listening to you trying to shout him down; no-one will trust your amateur obfuscation over his professional, accredited, and expert opinion.
    See how that works?

  2. I really don’t see the point in this endless speculation. This article offers zero in the way of hard facts whilst purporting to be science. It’s junk with big words, period. Mike Puchowicz has absolutely nothing concrete to offer but makes his point in a way that seems like he has. He’s doing nothing more than making assumptions on top of assumptions. Still, I suppose all web sites need click bait, and he’s obliged. But please don’t confuse this with a contribution to the debate. It does no more than metaphorically kick dust into the air,

  3. Interesting that Armstrong’s physiologist had the same explanation (weight loss=improved performance)in a peer reviewed, published article.

  4. Stupid bastards, it’s obvious. For years he had his saddle miles too low, anyone could see that. SKY simply made him put it up a little bit every 6 months. It’s still too low but when he finally gets it to where it always should have been, he’ll win another three TdF’s


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