2. Back extension
The back extension bench is a time-tested core builder, but its mechanical twin is the black sheep of back exercises. Repeatedly flexing your lower back under a load can cause injury to the lumbar discs, and the rigid position the machine holds you in doesn’t allow your core, glutes, and hamstrings to contract as they should to protect you.
Instead, strengthen your lower back with exercises that force you to maintain the natural arch of your lumbar spine.
Use these instead:
Body-weight Back Extension
Bent-over row (shown in the picture above)