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.
To illustrate, consider what might be expected from a weight loss mechanism if performance change is modeled from an observed baseline climb. For example, using the finishing climb on stage 10 of the 2015 Tour de France, a Froome like rider (67 kg, CdA .35, Crr .004, drivetrain loss 2.4%) would need an average 419 watts according to the Martin model on cyclingpowerlab.com to finish the 14.89 km, 7.22% climb in the 40 min 54 sec as Froome did in the race. Maintaining the same power but increasing his weight, Froome would have finished this climb in 41 min 42 sec at 69 kg, and 42 min 30 sec at 71 kg according to the model. So the weight would have put him back by 48 sec and 1 min 36 sec respectively. Those times would still have been good enough for 1st and 4th on the stage that day if we substitute in the simulation for Froome’s actual time. The caveat here is that the simulation does not account for accumulated fatigue over multiple climbs.
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, 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.
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