You can do this exercise either at the gym or at home. If you prefer to do them at home, you can either purchase free weights or use item like water bottles or soup cans.

This exercise works your trapezius, which are the muscles in your upper back, and your deltoids, which are your shoulder/upper-back muscles.

1. Stand up straight with your feet shoulder-width apart and knees slightly bent. With a weight in each hand, bend your arms at the elbow so that your hands are near your chest.
2. Punch your right arm across your body in line with your shoulder, keeping your core tight. Return that arm to the starting position.
3. Punch your left arm across your body in line with your shoulder, remembering to keep your core tight. Return that arm to the starting position.
4. Alternate punch the the right and left arms for 30 seconds to one minute to complete one set.
5. Perform three to four sets.