Overextending the lumbar. This creates compression on the spine under load.
Pressing from 90 degrees. This causes a shoulder impingement with every rep.
Extending the wrists. This compresses and stresses the wrist joints.
Starting the press from the delts and clavicle. This one isn't necessarily bad, but it's not optimal. It puts excessive shearing force on the front of the shoulder and creates a leak in time under tension, causing you to miss out on some growth opportunity.
Good Press
Here's how to get more out of it and prevent injuries:
Take a split stance to make your pelvis neutral and put your low back in a safer position.
Engage the core to create a solid foundation to press from.
Press from 45 degrees or closer to create more space for the upper arm bone to articulate with the shoulder bone with no impingement.
Flex the wrists. Think about keeping your knuckles straight up. This will give you optimal joint stacking.
For more time under tension and more hypertrophy, press from around nose or eye level. This will make it easier to maintain a braced torso and it'll intensify the movement.
2. Lateral Flye
Bad Flye
It's the basic chicken wing. When you lead with the hands instead of the elbows, it creates a lack of engagement of the delts.
Good Flye
Lead with the elbows and don't bring the dumbbells higher than your elbows. You'll feel it SO much better.
3. Upright Rows
Bad Upright Rows
This one has two main problems:
Hands too close together. This shortens the range of motion of the traps and decreases the effectiveness of the exercise.
Standing up straight. This decreases trap engagement and puts unnecessary stress on the low back.
Good Upright Rows
If using a barbell, put a couple feet between your hands to increase range of motion and stimulate the traps more. If using dumbbells, don't pull them up straight – pull them away from each other and up, creating a J-like lifting path.
Lean over slightly, engage your abs, and spread the floor. This will engage your glutes and create more stability in the pelvis and low back.