Vertical pushing movements can be seen in shoulder presses and in many of the Olympic lifts. Similar to chest press machines, seated shoulder press machines fail to recruit the glutes and abdominals, both important postural muscles.
Furthermore, stabilizer muscles such as the triceps, biceps, forearms, and upper back lose the opportunity to assist in the press. This creates once again, weak links in the human movement chain.
A great alternative is the dumbbell standing shoulder press. Each arm works independently, thus enhancing muscle balance and stability. Working muscles not only push the load upward, but also keep the dumbbells moving smoothly in the proper plane of motion. And all the while, the postural muscles maintain balance and stability in the body.
I guarantee that free weight standing shoulder presses will dramatically increase the challenge over the seated shoulder press machine. If you need to decrease the load, so be it. At the end of the day, your strength gains will be complete.
Make it a great day!