Originally Posted by
mkadam68
A couple thoughts:
- Ratio of FTP doesn't have anything to do with ratio of kcals when comparing two individuals.
Who are riding in the same group and taking the same length pulls.
Riding solo it's the most significant thing because the intensity you pick is some fraction of FTP - maybe 105% for hard 10 minute intervals, 85-95% for an hour sweet spot ride, 60% for a century.
At the same perceived intensity a big fit guy with a 300W FTP can do 100% better than some one out of shape at 150W.
- If speed is the same, moving a larger mass requires more energy production than a smaller mass, therefore more kcals expended.
Disregarding the solo ride scenario where speed can be whatever it needs to be -
That's only appreciable at low speeds (where rolling resistance dominates power demands) and on hills (where most of your power is going into hauling your carcass to the top).
On dead flat ground a 145 pound climber might take 158W to cruise at 20 MPH and 174W after he grows to 250 pounds in middle age. That's 10%.
OTOH a 2 MPH speed increase may demand 204W from the lighter rider burning 30% more calories over the same time or 20% more over the same distance.
- The more efficient an engine is (human body), the less energy is required for the same power output, i.e.: fewer kcals for the same wattage.
Cycling metabolic efficiency varies from about 20-25% or .95 - 1.19 C / kilojoule. The 25% variation from efficiency pales compared to the 100%+ variation in FTP or the same fraction of it.