system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 How does bulking make it easier to gain muscle?
gpt
Building muscle costs a lot of energy. Putting on a single kilo of muscle mass costs about 2 days worth of food. So the body is reluctanct to build up extra muscle except in times of plenty.

By bulking (a diet that's rich in calories in general and protein in particular) and exercising (using those muscles!) you're signalling to the body that it's the right time to get that extra musclemass.