Which Size of FlexBands Is Best for Assisted Pull-Ups?. Part of the series: LS - Workout Advice. It's important to get the right size FlexBands so that you don't take away from the movement and you hurt yourself. Find out which size of FlexBands is best for assisted pull-ups with help from a former University of Texas Longhorns football player, ACE-CPT, NSCA-CSCS, CEO and Founder of Nedufitness in this free video clip.