I’m not sure I agree entirely with the BBC summary, given the assumptions made in the study. No barriers have been found, in fact no barriers have even been tested in the study. This is a statistical trend only, surely?
Nordic skiers and TdF cyclists buck that trend at 3-5x BMR
I’m also not sure that cyclists are on a break in between major tours.
Also, regarding the TdF analysis:
“While neither group exceeded the apparent SusMS ceiling (Fig. 1A), it is unclear whether their above-average energy intake reflects special nutritional strategies (e.g., infusing glucose intravenously) or individual biological variation. Second, the signaling mechanisms linking energy imbalance to the body’s central regulation of activity, and that ultimately prevent humans from exceeding the observed SusMS versus duration curve, remain unknown.”
The chart in the study shows that it trends towards (and under) 3 the longer the event goes on. I think even the TdF is too short and so 3-5 seems about right.
Again the study itself talks through some theories as to what physiologically may be causing this limit. The gut/bloody systems ability to transport is either limited or decreases in capacity during prolonged periods of stress. This is all my relatively limited understanding.