Curls target the muscles in the upper arm.
Curls provide an excellent workout for your upper arms, and the many variations of this basic exercise work your arm muscles in slightly different ways. One variation is the supinated dumbbell curl that can be performed seated on a workout bench or standing. Although this curl targets the upper arm, several other muscles are used to execute this move.
In the supinated curl, you hold your arms so your palms face up. This concentrates the focus of the exercise more intensely on your biceps than holding the weights in a neutral position as in the hammer curl. Sit on a workout bench with your feet flat on the floor or stand with your feet about hip-width apart. Hold a dumbbell in each hand. Begin with the weights at your thighs. Your arms should be extended without locking your elbows. Keeping your elbows close to your waist, flex to slowly raise the dumbbells toward your shoulders. Pause and then slowly lower the weights back to the start position. Repeat 10 to 12 times.
Target and Assister Muscles
Your biceps are comprised of two muscles that extend from your scapula to your forearm and run along the front of your upper arm. They are responsible for arm flexion; that is, when you bend your elbow to bring your hand to your shoulder during a dumbbell curl. Additional muscles, known as synergists,or assisters, help the biceps perform the supinated curl movement. The two main synergists in this exercise are the brachialis that lies under the biceps and the brachioradialis, located in the forearm near your elbow.
The Stabilizing Muscles
Although they aren't being actively worked, several muscles help stabilize your body during any exercise. In the supinated curl, the deltoids and trapezius, wrist flexors and abs all work together to control your body movements. In any curl, you want to keep your shoulders square, not hunched, and this control is aided by the deltoids and trapezius. The wrist flexors come into play to stabilize the weights in your hands, while your abs help stabilize your torso.
A variation on the supinated curl is the preacher curl. In this exercise, your upper arm is supported by an angled bench. This keeps the upper body stabilized to hone in on the biceps. Rest your upper arm on the back of a workout bench that is set to an angle. The top of the bench should hit your arm pit. Hold a weight with your palm facing up and perform a curl slowly and smoothly. During the exercise, do not arch your back, twist or swing the arm to lift the weight.