The Jefferson Curl is a highly debated exercise in the world of strength training, mobility, and injury prevention. The exercise is a slow, weighted spinal flexion mobility exercise that emphasizes segmental control through the entire posterior chain. Despite its perceived benefits, the Jefferson Curl is not for everyone.
The Jefferson Curl involves standing on an elevated surface holding a barbell, dumbbell, or kettlebell in your hands, feet shoulder-width apart. From this standing position, you slowly roll down one vertebra at a time, allowing the spine to flex as you lower the weight toward your feet. After reaching your end range (often below the toes), you reverse the movement and slowly roll back up.
One of the biggest misunderstandings with the Jefferson Curl is why it’s being performed.
However, loading the spine in full flexion changes the risk profile significantly. So the purpose of the exercise matters, a lot.
Forward flexion can increase pressure on the intervertebral discs by 50-100%. Adding weight multiplies that stress.
| Posture | Estimated Disc Pressure |
|---|---|
| Standing (neutral) | ~100–120% body weight |
| Sitting (upright) | ~140% |
| Forward Flexion (no load) | ~150–200% |
| Forward Flexion (with ~20 kg load) | ~275–340% |
When bent forward with weight you experience an anterior shear force on the spine. With the spine in neutral alignment the erector spinae muscle group (small muscles along the back) provide strength and protection for the back. However, when the back is flexed forward in an arched position, these muscles are lengthened and lose some of their mechanical leverage. This results in more stress being placed on the ligaments and discs of the spine as the capacity of the spine to counteract shear is reduced by ~23–43%, depending on various tissue properties.
| Spinal Position | Erector Spinae Role | Shear Resistance |
|---|---|---|
| Neutral Spine | High engagement; good mechanical leverage | Strong |
| Slight Flexion | Moderate engagement; reduced leverage | Reduced |
| Full Flexion | Low engagement; line of pull ineffective | Significantly weakened |
Dr. Stuart McGill, a renowned expert on low-back injuries, compares the spine to tree branches. A flexible bendy spine is like a young, thin tree branch. The young tree branch is very flexible and allows a lot of movement in all ranges of motion, but with continuous bending under load, damage starts to occur. A strong/stiff and well supported spine is like a thick solid tree branch. The thick branch will have greater load bearing ability, but if forced to bend it and hold a load it could result in catastrophic injury.
In a forward flexed position with the back slighty arched, the muscles aligning the spine are at a mechanical disadvantage and additional stress occurs to passive structures of the spine (discs and ligaments). This is why repeated loaded flexion is associated with increased risk of disc herniation in some individuals.
When attempting to build strength it is important to consider the longevity and health of your spine. Look to maintain a neutral, strong, and stable spinal positioning by implementing the ‘Big 3’ movement habits. When working on maintaining or improving mobility you may want to consider unweighted exercises in a controlled environment, such as the cat cow exercise.
