I won a sore elbow from beating a 17 year old at an arm-wrestling contest, in camp once, back in the Hoods in the Woods days. I wore him down. He was a 300 pound Samoan named Vai.
As a kid, I somehow wore my brother down. He is 5 years older than me, and I was wiry. He wasn't 300 pounds, yet, but considerably bigger.
Endurance!
My new groundman is 36 and is training as a body builder. IDK that its the ideal fit for tree-work. Seems like Crossfit would get people ready for tree-work. IDK, haven't gone to the 'gym' in, IDK, 20 years.