For an interesting look at the factors involved in energy consumption, speed, weight, headwind, grade, etc. this bicycle calculator is pretty interesting:

Bike Calculator

For a given rider and bike going 20 miles with no elevation, what is your guess as which requires more calories: pedaling 20 mph; pedaling 12 mph; pedaling 12 mph against an 8 mph headwind; or, pedaling 15 mph against an 8 mph headwind?

Answer:

1. 12 mph requires the fewest calories... ~359

2. 12 mph against an 8 mph headwind requires about double the calories as 12 mph with no wind, over the same 100 minutes... ~739

3. pedaling 12 mph against an 8 mph is about the same number of calories as pedaling 20 mph with no wind but takes 40 minutes longer.

4. And what about 15 mph with an 8 mph headwind? The ride is 20 minutes quicker than 8 mph with a headwind and 20 minutes slower that 20 mph without a headwind and requires about 200 more calories than either. ~ 931

And, for BONUS points, how does pedaling at 8 mph on a windless day but up a 5% grade compare with the above?


Same 20 miles but 150 minutes. ~1677 calories.


But-- what 20 mile ride requires the most power?


That would be... 20 mph with no head wind (215 watts); going 15 mph against a 8 mph headwind comes in second (203 watts); and, going only 8 mph but up a 5% grade comes in at 3rd (195 watts). 12 mph against a headwind requires more power (129 watts) than 12 mph with no wind (63 watts).


So, what activity uses the most energy per unit of time?


Going up a 5% grade at 8 mph consumes 1677 calories in 150 minutes. However, pedaling 20 mph with no headwind for the same 150 minutes would consume 1,847.5 calories.