When pullups are done using correct form, each arm should be supporting 50 percent of the body weight throughout the entire movement, including hanging at rest, according to Physical Living. However, most people have a stronger arm and a weaker arm.
Right-handed individuals tend to favor the right arm. A Workout Routine reports that it is very difficult for individuals to use their right and left arms equally when performing bilateral exercises such as the pullup, because the dominant arm naturally takes over the exercise. Performing unilateral exercises such as dumbbell curls to strengthen the weak arm can correct the imbalance so the body can perform bilateral exercises using both arms equally.