Hamstring exercises grow different muscles: curls vs hinges
In short
Nordics concentrated growth in semitendinosus (+24.4% volume), while stiff-leg deadlifts favored semimembranosus (+11.2%). Pair a hinge with knee flexion; the seated leg curl was tested for acute damage, not long-term growth.
Nordic training concentrated muscle growth in semitendinosus (ST), with a +24.4% volume change. Stiff-leg deadlift training (SLD) favored semimembranosus (SM), at +11.2%. Choosing a hamstring exercise also changed where growth was concentrated. The comparison included biceps femoris long head (BFlh), so treating the hamstrings as a single growth target misses the result.
Did seated leg curls demonstrate the same growth pattern?
The seated isokinetic leg curl appeared only in the acute experiment. Researchers used changes in shear modulus, a measure of stiffness, to assess damage, and muscle volume to assess hypertrophy in the chronic experiment. These outcomes answer different questions. The table separates them rather than presenting an acute stiffness increase as new muscle tissue.
| Exercise | Acute shear modulus change | Chronic muscle volume change |
|---|---|---|
| Seated isokinetic leg curl | ST +62.2%, largest increase | Not measured |
| Nordic hamstring exercise | ST +33.0%, largest increase | ST +24.4% |
| SLD | SM +16.0%, ST −9.0%, BFlh +11.4% | SM +11.2% |
After SLD, the between-muscle differences in shear modulus were not significant. The ST value of −9.0% is not evidence of lost muscle volume. Leg curls showed a strong acute ST response, but the experiment does not supply a leg-curl growth percentage or establish the same response for every commercial curl machine.
Why did knee flexion and the hinge favor different muscles?
EMG-informed modelling estimated activation, operating length and force for the muscles. For knee-flexion exercises, the adaptations were linked mainly to the longer modeled operating length of ST and, to a lesser extent, its force. The SLD result did not fit that explanation: force differences between muscles did not explain the SM adaptation. Predictive models identified the most damaged muscle in 82% of cases and the most hypertrophied in 75%. Those figures describe model performance, not a lifter's probability of growth.
What belongs beside a deadlift in a Big 3 routine?
- Include a hinge and a knee-flexion movement such as a Nordic or leg curl. This is a programming application, not a tested combined protocol.
- Record each exercise's load, sets and reps in fairlift, then check whether knee-flexion work disappears from the routine.
- Read Big 3 performance and the Muscle Index as strength records; neither measures the distribution of hamstring growth.
An RDL is a practical hinge option, but it cannot inherit the SLD growth percentage. A strong deadlift does not establish that knee flexion has been trained. The findings do not define an optimal dose for a combined routine.
Frequently asked questions
Which muscles grew most with Nordics and stiff-leg deadlifts?
In the chronic experiment, Nordic growth was concentrated in semitendinosus (+24.4% volume) and stiff-leg deadlift growth in semimembranosus (+11.2%). That does not mean every other hamstring muscle failed to grow.
Is the +62.2% after leg curls a hypertrophy figure?
No. It is the increase in semitendinosus shear modulus after seated isokinetic leg curls, used to assess acute damage. Leg curls were not included in the chronic hypertrophy experiment.
Can a strong deadlifter skip knee-flexion exercises?
Big 3 strength alone does not establish knee-flexion training exposure or evenly distributed hamstring growth. Pairing a hinge with a Nordic or leg curl and logging each movement's work is a practical application of these findings.
Can Romanian deadlifts be assigned the same growth percentage?
No. The +11.2% semimembranosus volume change was reported for stiff-leg deadlifts. RDLs are a programming example of a hinge, not an exercise tested for that result here.
Source: PubMed (published )