Originally Posted by SabreMan
Wait! Different engines -- bodies in this case -- burn fuel at different efficiencies. Assuming you are in better condition then she is, she has to burn more calories to accomplish the same amount work/power.
Glenn in Omaha
Not really, humans all have roughly the same 18-20% conversion efficiency. You may be thinking of maximum power-output at LT or VO2-max which
does vary between people. This is power-produced-per-oxygen consumed. But the conversion efficiency is still the same as in calories-glucose-per-Watt-produced.
So differences in fitness may result in different maximum power-output, but for any given amount of power-produced, it should be similar calories-burnt. Sure for one person it may be at 100% of their LT/TT pace, while for another it may be only 80%.