The bent-over rows with dumbbells are very effective for training your trapezoids, lats, rear shoulders and biceps.
1. Stand with your feet slightly less than shoulder width apart
2. Position your hands directly below your shoulders
3. Tip your upper body forward
4. Completely extend your arms and shoulder blades
5. Move your arms upwards, with your elbows close to the body
6. Actively pull your shoulder blades together
