[alistairSH]

seems easier to burn energy on a bike than other forms of exercise

I'm not sure this is true. Cycling isn't weight-bearing (you're sitting down) and only engages the large leg muscles. Running and rowing likely provide more calorie burn for a given RPE (rate of perceived exertion) over a fixed time period. Running because it's weight-bearing; rowing because it engages more muscle groups. That said, you can probably cycle for more hours total, if you have nothing else to do.

[naasking]

Running doesn't burn as much as you think because your muscles store energy elastically on the eccentric phase of each step. This removes a lot of energy needed for the subsequent concentric part.

Contrast this with cycling which is pretty much all concentric contractions.

[alistairSH]

Interesting, hadn't considered that aspect. Just goes to show how complicated and counter-intuitive this can be.

[naasking]

Evolution is great at optimizing! Running is so efficient for humans that some human tribes use it to hunt (persistence hunting). They literally run their prey to exhaustion then just walk up and kill them.