Activity is something based on posts so it's kind of related but at the same time it doesn't mean that if you post more you gain more activity.However,if you don't post for let's say 6 weeks you will not gain any activity.If you have posted in just 1 of those 6 weeks,no matter how many posts you made in that 1 week you will still gain a limited activity based on a certain period which will not be for the whole 6 weeks.I hope I explained it at least somewhat understandable