You have to lean farther forward during a deficit deadlift than you do during the standard exercise, says Bryant Thomas, Tier 3+ trainer at Hudson Yards in New York City.
That’s all well and good if you have flexible hamstrings and hip flexors—but in most people, these muscles are tight. In turn, your pelvis is pulled out of neutral and into an anterior or posterior tilt, Thomas explains. When that happens, your lower back is more likely to round during the deadlift, which puts added force on your lumbar spine and increases your risk of injury.
To test your hip flexor and hamstring flexibility, try this: Lie on the ground with legs extended, toes pointing up. Keeping both legs completely straight, raise your left leg as high as you can without lifting your right leg off the ground. If you can raise your left ankle past your right knee (and vice versa), you’re cleared to perform deficit deadlifts.
The bottom line:
During this lift, never stand on a platform that’s taller than three inches, Thomas says. (That’s about the height of one step sans risers.) Your shoulders should always remain above your hips at the bottom of the movement.
If you fail the above test, target your posterior chain instead with good mornings, Romanian deadlifts, and hyperextensions on the machine.