Arms....so sore!

I went to the gym yesterday with my friend V to do an upper body workout. We did our usual weights but I wanted to add in an exercise to help me improve my pull-ups (because I can do 0 at the moment). Someone suggested I try standing on a chair, then jumping up and slowly lowering myself down. Dear god! It's waaaaayyy harder than it sounds and I'm paying for it today. It hurts even to straighten my arms! I guess that's a good sign!