Jefferson curl EMG needs its load context
In short
In 21 trained adults, the Jefferson curl produced higher EMG in selected back and hamstring muscles than the RDL at the same load. Five repetitions do not establish better growth or safety. Record the exercise and loading context.
The same barbell weight does not make the Jefferson curl and Romanian deadlift equally demanding. An International Journal of Sports Physical Therapy study measured surface EMG while 21 resistance-trained adults performed five repetitions of each movement on a 30-cm platform. The load selected during the Jefferson curl was reused for the Romanian deadlift (RDL). The comparison answers a same-weight question, which is narrower than asking which exercise deserves a place in every training plan.
Where did activation differ?
| Muscle | Jefferson curl | RDL |
|---|---|---|
| Upper erector spinae | 62.84% MVIC | 44.52% MVIC |
| Lower erector spinae | 60.07% MVIC | 47.85% MVIC |
| Biceps femoris | 54.18% MVIC | 41.54% MVIC |
These are mean surface-EMG values normalized to maximal voluntary isometric contraction, or MVIC. Adjusted p values for the three comparisons were 0.003, 0.035, and 0.035. The middle erector spinae and gluteus maximus did not differ significantly. Load selection used a Borg perceived-exertion target of 16 during the Jefferson curl. Borg here uses a 6–20 scale; the number is not a score on a ten-point lifting RPE scale and does not specify repetitions in reserve.
What belongs in a comparable training entry?
- Keep Jefferson curls and RDLs as separate exercise records.
- Log load and repetitions, then note the platform, movement range, and exertion scale used.
- Compare the next session with the same movement and conditions; do not turn an EMG percentage into a load target.
The practical implication for fairlift is about preserving context. Copying an RDL load into a Jefferson-curl target assumes a relationship the experiment did not establish. Matching kilograms is different from matching a percentage of the maximum available in each movement. This single-session comparison also did not measure later muscle growth. Keep either accessory exercise separate from the deadlift 1RM used in the Muscle Index calculator. More activity in a measured muscle during five repetitions is not evidence that a competition-style deadlift maximum increased. This record-keeping recommendation is an interpretation of the study design, rather than a program tested by the researchers.
Surface EMG does not rank injury risk or prove that one movement is safer. This study is not a basis for prescribing heavy loaded spinal flexion to a new lifter or to someone with pain.
Frequently asked questions
Does the Jefferson curl build more muscle than the RDL?
The study measured activation during five repetitions, not long-term muscle growth. Greater EMG under these conditions does not establish superior hypertrophy.
What is Borg 16 on a ten-point RPE scale?
The study used the Borg 6–20 scale. It did not provide a conversion to ten-point lifting RPE or repetitions in reserve.
Does using the same weight mean equal intensity?
The external load was the same, but relative intensity was not matched to each movement’s maximum. Interpret this as an absolute-load comparison.
Source: International Journal of Sports Physical Therapy (via PubMed) (published )