Try This Arm Workout For Beginners, Designed by a Personal Trainer

This dumbbell arm exercise strengthens your chest while also recruiting your core.

• Grab a set of dumbbells, and lie face up on the floor with your legs in tabletop position and shins parallel to the floor. Press your lower back into the mat to engage your core. Raise your arms toward the ceiling, palms facing each other, keeping the elbow joint slightly bent. This is the starting position.
• Keeping your torso stable, open your arms out to the side until your elbows are about two inches from the floor. Continue to press your lower back into the mat, and avoid letting your ribs flare open.
• Raise your arms back to the ceiling, bringing the weights together over your chest. That's one rep.
• Do 10 reps.