Here’s what I have done in the past–mind you, this was for shoulder, forearm, and GPP purposes, so you may want to modify this to suit your needs.
I would take 80lbs.DB’s and run as fast as possible up a steep hill–sorry, I can’t tell you the exact grade, maybe 30 degrees–for about 40 yards, then immediately turn around and do a controlled run back down.
When I hit the bottom of the hill I would stop just long enough to adjust my grip and run back up, and then back down the hill. That’s one set. Next set was a single lap up and back down. Final set another single lap. I allowed about 30 seconds rest between sets.
This is a killer for shoulders, back, traps,legs, forearms and especially GPP–your heart feels like it’s going to explode, especially in the summer heat; at least it did for me, but maybe that’s because I’m 46 y.o.