Chest wall recoils outwards.
Lungs recoil inwards.
During inspiration, as you're filling your lungs with air, your lungs are being stretched (against its recoil force) while chest wall expands (in favor of its recoil force i.e. outwards).
During expiration, the lungs have to collapse (in favor of its recoil force i.e. inwards) while chest wall moves in (against its recoil force).
So imagine you're expiring, the lungs are trying recoil inwards whereas the chest wall is trying to recoil outwards. But due to the pressure gradient (won't go into the detail of this cuz it's a whole story in itself), the lungs win because it has a stronger inward force.
Now if something increases the recoil force of the chest wall (which is outwards) it'll have more chances of winning so you'll have to put in extra effort to make the lung recoil (inward force) win for the sake of expiration.
Just like a tug of war. Team A is lungs, team B is chest wall. For expiration to take place you need team A to win. But if the force of team B is way too strong and pulling it outwards, then you'll need team A to work EXTRA hard to overcome that force and pull towards its side (inward) so that expiration can occur.
I hope I was able to put the idea into words correctly.
