It never ever feels easier!
I think to really be good at fitness-ing you have to get to a point where you like/need your heart to get to explodey-levels. I'm certainly not there... and am just hanging on until I can stop... but I'm at the point where I recognize it's a good place to be and the stopping will be oh so good the more I push.
Ugh... why are knees always the first things to go? Don't they know how useful they are? They are so useful... knees, be more invincible... please!