These can be done with a Kettlebell (KB) or a dumbbell, even a resistance band! I call them 21’s because you do 3 different exercises with 7 reps of each.
First – start with the weight (KB/dumbbell) upright, only lower your arm to 90 degrees before raising back up. Do 7 reps.
Second – start with the weight down, with arm extended, only raise your arm to a 90 degree angle before lowering back down. Do 7 reps.
Third – Do a full bicep curl with your arm extended all of the way, curling all of the way up towards your shoulders. Do 7 reps for a total of 21 reps.