You are in a supine position when you are lying on your back with your face upwards. A supine dumbbell press is a regular dumbbell press, usually done on a weight bench, but it can also be done on the floor or on a stability ball. This is a compound exercise that works several muscles in your upper body.
The Exercise
Lie back on a weight bench with your feet on the bench or flat on the floor. Extend your arms straight above your chest with a dumbbell in each hand and your palms facing forward. The dumbbells should almost touch. Pull your shoulder blades together and down. Maintain this position throughout the exercise. Inhale, bend your elbows and lower your arms. Stop when your upper arms are parallel, or slightly below parallel, to the floor and your elbows are at a 90 degree angle. Exhale and press the dumbbells back overhead.
Primary Mover
The primary mover is the muscle that performs most of the work during an exercise, the target muscle. For the supine dumbbell press, the primary mover is the pectoralis major. This is your largest chest muscle that originates at the sternum and ribs on the interior side and attaches to the humerus, the upper arm bone, on the exterior side. One of the functions of the pectoralis major muscle is transverse flexion, moving the upper arm towards the chest with the elbows facing out to the sides.
Synergists
Synergists are muscles that assist the primary mover in completing a movement. For the supine dumbbell press, the triceps and shoulder muscles help the chest. The triceps muscles extend the elbow joint, which is what occurs as you press the dumbbells overhead. The shoulder muscle, specifically the anterior, or front, deltoid assists in transverse flexion, pulling the upper arm towards the chest.
Stabilizers
Stabilizer muscles stabilize a joint or support the trunk so the primary mover and synergists can accomplish a movement. The rhomboids, small muscles in your upper back, and the biceps, the muscles on the front of your upper arm, act as stabilizers during the supine dumbbell press. Your rhomboids keep your shoulder blades pulled together and down. The biceps muscles contract at the shoulder and lengthen at the elbow, stabilizing these two joints as you press the dumbbells overhead.
