Yeah I heard that using not heavy weights but lot of reps makes you gain strength and give you "cuts" but not massive muscles... I KNOW i have little to none upper body strength beceause I can't even do a push up, alhtough I'm surprised I can practice handstand and Invert with not much problem, so I decided to gain some strength on my upper body and arms.
Currently I'm doing at least 100 sit ups(=[ im getting lazy with those... I used to do at least 500 but not anymore) with 3 lbs dumbells on each hand... Hold that close to your chest like you are holding exercise ball. And other workout that involves those 2 Three pound dumbells... They are not heavy to give you bulky manly muscle yet they seem to help me with gaining bit strength
