The Jefferson curl is a slow, weighted forward roll of the spine. Standing on a box with a light weight hanging from your hands, you tuck the chin and round the back one vertebra at a time until you hang at the bottom, pause, then unroll back to standing. It is a loaded stretch for the hamstrings and back, not a lift to load heavily.
Nobody is credited with inventing or naming it. The name is usually assumed to borrow from the Jefferson lift, a straddle deadlift named after the circus strongman Charles Jefferson, but the USAWA’s history of that lift never mentions the curl. GymnasticBodies, Christopher Sommer’s gymnastics strength programme, calls it a mainstay of its courses. Brolic lists it as Jefferson Curl (Dumbbell) and Jefferson Curl (Barbell), with “Dumbbell Jefferson Curl” and “Barbell Jefferson Curl” as aliases, and logs both as two-sided exercises in reps.
Muscles worked
Brolic tags the lower back and hamstrings as primary, with the glutes as secondary, on both entries. Tom Merrick calls it a loaded hamstring stretch and one of the best there is. Emmet Louis, of Modern Methods of Mobility, treats it as a mobility drill: peel each vertebra off the one below, then restack them in order.
No study measures it. A PubMed search on October 7, 2026 for “Jefferson curl” in titles and abstracts returned nothing, so nothing establishes what it does compared with an unloaded forward fold or a Romanian deadlift.
Set up on a box
Stand on a box or bench with the toes at its edge. Louis sets the feet with the toes at the edge so the weight can hang clear of the box.
Hold something light. Kettlebells, a barbell, a dumbbell or a plate all work, says Merrick; Louis uses a pair of kettlebells. Louis starts people at 10 kg and says not to go excessive: the weight is there to work the motion. Merrick’s rule is the least weight that gets a response, perhaps 5 or 10 kg at first and 15 or 20 kg later; too much weight too soon is the third of his three mistakes.
Lock the legs by contracting the quads. Merrick’s second mistake is bending the knees. Both the calf and the hamstring cross the knee, so a straight, actively locked leg is what stretches the hamstring, and the working quad supports the knee.
Roll down and back up
Tuck the pelvis, hollow out and tuck the chin. Louis has the lifter tuck the pelvis and hollow the trunk, then let the head relax down from the top. Merrick stands tall, tucks the chin and keeps it tucked all the way down.
Flex the spine one vertebra at a time, from the neck down. This is a spinal articulation, not a hip hinge. Merrick’s first mistake is the hips travelling back, or the movement starting from the lower back; the roll begins at the top of the neck and works down segment by segment to the base of the spine.
Let the weight hang. Louis has the shoulders spread and the weight pulling down rather than held, and lets it roll forward once it reaches the feet.
At the bottom, reach for the floor with the quads still on, and hold. Merrick’s bottom position is your maximum forward fold with the weight hanging and the legs locked, held for a few seconds.
Come back up from the bottom of the spine. Merrick reverses the roll vertebra by vertebra from the base; Louis resets the spine from the bottom and squeezes the glutes to stand.
Reps and holds. Merrick does about five repetitions with a slight pause on the last. Louis prefers reps with a hold on the last one; his video description suggests three to four sets of five with a 10 to 15 second hold.
How it differs from a Romanian deadlift
| Jefferson curl | Romanian deadlift | |
|---|---|---|
| Spine | Rounds, one vertebra at a time | Held flat |
| Hips | Stay over the feet | Travel back |
| First movement | Chin tuck | Hips back |
| Load | Light; the stretch is the point | Heavy; the lift is the point |
Merrick’s test is the first movement: if the hips go back first, you are hip hinging, not Jefferson curling. His straddle variation, feet wide on the box, is done the same way.
Logging
Brolic logs both entries in reps. Enter one dumbbell or kettlebell for the dumbbell entry (note a pair), or the total on the bar for the barbell entry (the barbell calculator adds it up). Note the box height, the hold on the last rep and whether the feet were together or straddled: the load barely changes, and range and control are what progress. The free workout log has room for that, and the weekly set tally shows these sets beside your other hamstring work.
Common questions
Knees bent or straight? Straight and locked by the quads, says Merrick: bent-leg and straight-leg hamstring flexibility are trained differently and transfer differently.
It hurts. Shorten the range, lighten the load or stop. Pain is not a cue to work through, and nothing here is advice for an existing back problem.
Sources and method
- Tom Merrick: Jefferson curl, Do It Right — the three mistakes, locked legs, load figures, reps and the straddle; automatic captions.
- Emmet Louis: How to do a Jefferson curl — toes at the edge, the 10 kg start, the pelvis tuck and the glute squeeze; automatic captions and description.
- GymnasticBodies: The Jefferson curl — the 5 lb start; no credit given for the exercise.
- USAWA: Jefferson lift origin — Charles Jefferson and the straddle deadlift; no mention of the curl.
- Brolic catalog — names, aliases, logging mode and muscle tags.
Load figures are the coaches’ starting points, not optima from a trial.
