Try to lift the dumbbells mostly through your shoulders, not your lower back.
Outer portion of your shoulder.
Front portion of your shoulder.
Center region of your back, spanning from the pelvis to just below the neck. However, parts of it are hidden beneath other muscles. The lower portion is the most visible.
Dumbbells
When gripping dumbbells, make sure you position your hands in the middle of the bar and not at the end next to the plates.
Flat Bench Without Rack
If you can't find this bench, consider using a flat bench with rack instead. If your exercise requires you to use a barbell or bar, you cannot substitute. If you do not need to use either, you probably can substitute.
Exercises that target the same primary muscle groups and require the same equipment.
Exercises that target the same primary muscle groups with different equipment