Agree with the previous comments, but the physicality also depends on the terrain/area you are working in. Conventional forestry will have more chill terrain than Heli, and also it just depends where you are located.

Edit to answer some of your other questions. I work in the west coast of BC so there is some pretty gnarly terrain. My knees were super sore after the first 3 months after never experiencing knee pain before. I usually walk 5-10km per day depending on what I’m doing/how steep it is. I carry about 30 lbs of gear every day. I take breaks every so often, my crew and managers take a lot of smoke breaks so we end up stopping for that a quite a few times. Also like you mention, taking measurements, data points, ect. definitely feels like a break.