[hgomersall]

Yeah, I thought this. There's clearly an amount of exercise that will cause you to lose weight. An interesting question is whether your body prevents you from achieving that.

Cycling was always interesting to me in this context because it seems easier to burn energy on a bike than other forms of exercise.

[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.

[ajuc]

When cycling there's this "wall" you hit after a few hours. At least I do. After that it's much harder to keep pace or go uphill.

[nradov]

There's nothing special about cycling. You can deplete your glycogen stores and hit the wall with any aerobic activity. If you have a healthy metabolism and stay in heart rate zones 1-2 then you'll mostly burn fat stores and can cycle for many hours without hitting the wall. At higher zone 3+ efforts you'll need periodic carbohydrate supplements to keep going.

[hgomersall]

Indeed, but you can keep going just about. I've properly hit the wall once, and that was an unpleasant experience - nearly fainting and seriously in danger of falling off my bike, but I think that was largely a hard removal of all accessible glycogen, and it was years ago when I was relatively green. Now I just tend to eventually find it hard and unpleasant.