system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is riding a bike uphill harder than walking

Riding a bike generally uses less energy than walking, because there is more efficient energy transfer. Why is this no longer true when you're riding uphill?
gpt
Because bikes can roll backwards. Your feet can’t glide backwards (unless your on ice).

When you walk uphill, the friction between your feet and the ground is enough to keep you from sliding backwards and losing progress.

But a bike, a bike can roll backwards. Yknow how easy it is to bike downhill? And how much speed you can build up due to gravity pulling you down? Well when biking uphill, you have to fight against that, and if at any point you stop the bike is going to start rolling backwards.

When you’re walking, if you stop you can just stand there and rest, biking you have to keep yourself from losing progress.