Generally, this situation is easy to see when doing bench press and barbell bending. The reason is that the biceps brachii muscle density of the left arm and the right arm is different, which leads to normal people. Generally the weak arm is the left arm. (Left-handed people are all right-handed) Because of the usual physiological habits, it is suggested to bend with a double-headed hammer with a single-arm dumbbell or kettle bell to train the muscle endurance of the weak arm. For example, I take two 10KG left hands as weak arms, and my left hand is 4x65438.