Depending on what type of weight you use, the pullover exercise can focus on developing your chest or your back. When you use a dumbbell for the straight arm pullover, you target your chest muscle. When your hands come together and hold a dumbbell over your chest as they do during the pullover, your shoulders have to internally rotate. When your shoulders are internally rotated position, it's your chest muscle that does the work to extend your shoulders during the pullover.
To perform the straight-arm dumbbell pullover, lie on your back on a flat bench and hold a single dumbbell with both hands. Hold the dumbbell over your chest with your arms fully extended. Keeping your elbows straight, lower the dumbbell back behind your head until your arms are about parallel with the floor, and then extend your shoulder joints to raise the dumbbell back to starting your position.
The major muscle in the chest is the pectoralis major which features two separate heads, the larger sternal section and the smaller clavicular section. The clavicular head is up near your clavicle and is not active during the straight-arm pullover. However, the sternal head, which originates at your sternum and then runs out towards your shoulders and inserts at the top of your arm bones, is involved during the straight-arm pullover. You probably know how the chest squeezes your arms together during the chest press, but the sternal head of the chest muscle also extends your shoulders, pulling your arms down.
Other Contributing Muscles
A couple of other muscles are recruited during the straight-arm pullover to assist in completing the movement. The latissimus dorsi, which is the largest muscle in the back, and your posterior deltoid, which is located at the back of your shoulders, contract to help extend the shoulders. In addition, the triceps at the back of the upper arms contract to hold your elbows straight as your arms swing back and forth.
When you perform the pullover exercise with a barbell, your hands are positioned about shoulder-width on the bar. With your hands separated wider than they would be when you're holding a single dumbbell, your latissimus dorsi muscle in the back handles most of the work, while the pectoralis major becomes an assisting muscle. During dumbbell pullover, with your hands together, your shoulders are slightly adducted, or rotated inwards, and because of this, your pectoralis major is more dominant. To target your chest while using a barbell, hold the bar with your hands positioned side-by-side instead of shoulder-width apart.
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