Originally Posted by
asgelle
Interesting, but I'm not sure what I'm looking at. Was this a direct measurement of substrate utilization? I don't see data points on the graph so I wouldn't think so. It could be they measured gas exchange and then applied a model to correlate gas exchange to fat/CHO, but again no data points. Finally, did they simply apply a model to an assumed or measured threshold? That would be consistent with the smooth curve with no data points. If a model was involved, it raises the question of how accurate and accepted it is. The fact that whoever created this plot was sloppy with their axis labels doesn't help with their credibility. A reference would help.
Good points. Or as it were, I couldn't find a graph of what I wanted with good points on it. I found that one in a old forum, couldn't find the original. If you can find a better, I'd bookmark it. Someone on here used to post a B&W graph like this every time this subject come up, but I never could find their original. I can't remember who the poster was, not you I guess. It had smooth curves on it, too.
What the graph originators seem to have been ignoring is the calorie burn which is just a part of metabolism. Neither curve on the graph should start from zero, but why did they cut that off?. So yeah, the graph is indicative but maybe not accurate. Our normal 2000 calorie/day person burns mostly fat, but also some carbs in normal activity, so say 100 calories total per hour daytime. Fat burn then goes up to a max at 120w for this individual. For me, adding in carbs, 120w comes to around 425 calories/hr or so says TP for one of my roller rides, me not bothering with the calculation. The graph however shows ~525 calories total at 120w, and thus seems to include the BMR. So one data point doesn't seem to be too far off.