POLE PRUNING !!
The overhead pole saw work for several hours straight, is hardest for me.
All else, can be dealt with. If a pile is too big - cut it in half. If a chunk is too big, slice it in half. Too much brush, hire an extra temp.
The pole saw work never quite seems to ease-up the same way.
It probably differs for each of us, depending on how they are built. I saw a wrestler-build guy move mountains of limbs in a single arm-load - no problem.
There was a body-builder temp that helped drag limbs one day. I handed him my handsaw and told him to cut 6" off a 3" DBH branch end that was stacked on the trailer.
He started, and I said "STOP !! - you are using two hands. Try it with one to see what it's really like".
Using one hand, he chugged away for about 15 seconds and stopped to huff and puff after one cut. He had muscle mass, but not endurance with the handsawing muscle group.
I remember how hard handsawing was for me, the first 3 weeks of business.