Set-up: Find a spotter and a stability ball. Lie down on the stability ball with your shoulder blades retracted, your stomach and abs tight and your feet flat on the floor. Grip the dumbbell with a fully closed and tight grip, and lift it while bracing as hard as possible through the core. Start with a light weight to be sure you can handle the instability.
Lift: Forming a tight brace in your core to resist both the unilateral weight and the instability of your surface, lower the dumbbell in a straight line to your chest. Reverse the movement quickly while making sure the dumbbell travels in a straight line back up. Keep your feet firmly planted at all times, and your elbow close to your body.
Emphasis: Keep your shoulder blades together at all times and do not allow your shoulders to roll forward during the movement. Press to your chest, NOT your face. Do not bend your wrists, there should be a straight line through your forearm up to your knuckles.
Repetitions: Perform all prescribed reps on one side, then on the other. This counts as one set.
Muscle Roles in stability ball one-arm dumbbell bench press
Movement in Frontal, Transverse and Sagittal Planes