Marvin is working on improving his upper body strength. Presently he does 6 upper body exercises. His favorite is the shoulder press which he does 2 times per week using 10 pound bells and completes 2 sets of 8–12 repetitions. A change Marvin should make to increase his muscular strength in this area using the intensity principle is to increase the: amount of weight to 15 pound bells number of repetitions to 15–20 number of sets from 2 to 3 number of times per week to 3