Why when hikers are tired is it easier to hold the straps of our backpacks?

Question

When I start a hike, my hands and arms are free and easy. Towards the end I always find them clutching the straps of my backpack. Why?

Edit, for clarity: I always use a waist strap. I’m not talking about using my arms to lift weight off my shoulders. I seem to end up holding my shoulder straps, elbows pointed downwards, almost pulling the backpack downwards onto my shoulders and tighter against my back.

In: 310

Answer 1

Because when you pull the backpack into you, you increase the amount of weight being held up by friction (like gripping a lid harder to try to twist it off).

So there’s some relief from physics in the form of the frictional assist from the increasing normal force. Which reduces the weight held by your shoulders/back.