One Arm Dumbbell Shoulder Press

The one arm dumbbell shoulder press drives a single dumbbell from shoulder height to full extension while you sit with the back supported. Working one side at a time does two things a two-arm press cannot. It exposes the strength difference between shoulders, which a pair of dumbbells averages out without either of you noticing, and it creates an asymmetric load that the trunk has to resist, so the obliques on the opposite side work throughout the set even though you are sitting down. The deltoids and triceps handle the pressing itself, with the upper back stabilising the shoulder blade. Keep the ribs down rather than arching the lower back to gain range as the weight gets heavy, and finish with the arm stacked over the ear rather than out in front of it.