Starting Position: Stand holding dumbbells in your hands with a closed, neutral grip (thumbs around the handles with your palms facing your body). Position the dumbbells alongside your thighs with your elbows fully extended. Assume a split-stance position to stabilize your body, stiffen your torso by contracting your abdominal/core muscles ("bracing"), and depress and retract your scapulae (pull your shoulders down and back), maintaining these positions throughout the exercise. Your head and neck should be aligned with your spine.
Upward Phase: Exhale and slowly flex (bend) one or both elbows in unison until the dumbbell(s) near(s) the front of your shoulder. It performing alternating arm curls, the opposite arm should remain in the starting position. Perform the curl while keeping your torso erect (no arching your low back) or without moving your elbows forward. Maintain a neutral wrist position (wrist straight without any bend with your palms facing your body) and avoid shrugging your shoulders throughout the movement.
Downward Phase: Inhale and gently lower the dumbbells back towards your starting position until the elbow(s) is/are fully extended, keeping the dumbbell in the neutral position. Maintain your split-stance, torso and shoulder position and if performing alternating arm curls, repeat to the opposite side.