Nordic Hamstring Curls: The Evidence for Injury Prevention

A hamstring strain is one of the most common injuries in sprint and change-of-direction sport, and it is also one of the most preventable. A 2019 meta-analysis of 8,459 athletes found that adding a single exercise, the Nordic hamstring curl, to a training program cut hamstring injury rates roughly in half¹. That is a rare result in sports medicine: a large, replicated effect from one movement.

The evidence base behind that number is unusually deep for a strength exercise. Randomised controlled trials, cohort studies tracking eccentric strength as an injury predictor, and EMG work comparing the Nordic curl against other hamstring exercises all point the same direction. What is less well understood, even among coaches who program the exercise weekly, is why it works, and why so many teams still get a smaller effect than the trials suggest.

The number that keeps replicating

The headline meta-analysis pooled 15 studies and found a risk ratio of 0.49 for hamstring injury in groups performing Nordic curls as part of their program, a reduction of roughly 51 percent¹. A separate meta-analysis focused specifically on soccer players found the same effect size almost exactly: a risk ratio of 0.490 across five studies², despite differences in playing level, season length, and program design. Two foundational randomised controlled trials sit underneath these pooled results. In Danish men's soccer, 942 players were cluster-randomised to eccentric training or a control group for a season. The intervention group recorded 15 hamstring injuries against 52 in the control group, an adjusted rate ratio of 0.293³. A Dutch trial in amateur soccer, 579 players, found an odds ratio of 0.282 for the intervention group⁴. These are not small, underpowered studies. They are among the larger RCTs in sports injury prevention, and they converge on the same magnitude of effect that the pooled analyses report.

Why the hamstring fails in the first place

The mechanistic case for the Nordic curl starts with what actually predicts a hamstring strain. Two prospective cohort studies in elite footballers isolated the same two risk factors: low eccentric knee flexor strength and short biceps femoris fascicles. In 210 Australian footballers, players with preseason eccentric strength below 256 N were 2.7 times more likely to sustain an injury, and by the end of preseason that risk rose to 4.3-fold for players who remained weak⁵. A separate cohort of 152 elite soccer players found the same pattern from a different angle: eccentric strength below 337 N carried a 4.4-fold injury risk, and fascicles shorter than 10.56 cm carried a 4.1-fold risk, independently of each other⁶. Put together, these findings describe a muscle that fails not from being generally undertrained, but from a specific structural and force-generating deficit at long muscle lengths, precisely the position where a sprinting hamstring is loaded during late swing phase.

What the Nordic curl actually changes

This is where the Nordic curl's specificity matters. It is not simply a hamstring strengthening exercise among many. A controlled trial comparing the Nordic curl against a hip extension exercise over ten weeks found that both exercises increased eccentric strength, but only architectural adaptation in the Nordic group showed the large fascicle-lengthening effect associated with reduced injury risk, with effect sizes between d=1.77 and d=2.17⁷. A systematic review pooling 13 intervention studies confirmed this is not dose-dependent in the way many assume: both higher and lower weekly volumes of Nordic curls produced very large effect sizes for eccentric strength (g=2.12 to g=2.28) and fascicle length (g≥2.58) once the intervention ran six weeks or longer⁸. The most recent umbrella review, pooling 108 randomised trials, puts numbers on the physiological shift directly: eccentric strength increased by an average of 26.9 N·m and fascicle length by 0.90 cm, alongside a 56.8 to 70.0 percent reduction in injury incidence across the trial pool⁹. The exercise is doing two things at once, adding force capacity and adding usable length, and the injury-prevention literature suggests both matter.

Where EMG adds a layer trials cannot show

Randomised trials establish that the Nordic curl works. They do not establish which exercises come closest to replicating its specific neuromuscular demand, which matters for programming when the full Nordic curl is not tolerable early in a rehab timeline or a pre-season block. A systematic review of 29 studies covering 507 participants and 114 different hamstring exercises used surface EMG to rank biceps femoris activation across the exercise pool. The Nordic curl and isokinetic eccentric contractions produced the highest activation, above 60 percent of maximal voluntary contraction, with the ankle-dorsiflexed variant of the Nordic curl reaching 128.1 percent¹⁰. That is the kind of resolution a randomised trial cannot offer: not just whether an exercise category reduces injuries at a population level, but which specific variation is driving the highest recruitment in the muscle that actually tears. It reframes exercise selection from "add eccentric hamstring work" to a more precise question about which movement, and which joint position, is loading biceps femoris the hardest.

The gap between the trials and the training ground

The one variable that consistently separates strong trial results from disappointing real-world outcomes is compliance, and the literature is candid about this. A meta-analysis of four compliance-stratified studies found that intention-to-treat analysis produced a non-significant effect (RR=0.59), but restricting the analysis to athletes who actually completed the prescribed sessions dropped the risk ratio to 0.35¹¹. A separate review pooling 13 studies quantified the compliance threshold more precisely: athletes with greater than 75.1 percent session compliance saw a significant injury reduction, and consistency, defined as no more than three weeks between sessions, strengthened the effect further¹². The Nordic curl is unusual among injury-prevention exercises in that its efficacy has been directly shown to degrade with inconsistent dosing, not just diminish gradually. A team programming it twice a week and actually completing those sessions is working with a materially different intervention than a team that intends to but skips it during a busy fixture block.

What this means in practice: the injury-prevention case for eccentric hamstring work is about as strong as sports science evidence gets, but the exercise only delivers that evidence-backed effect when strength and architecture actually change, and that requires enough consistent, adequately loaded sessions to show up as a training effect rather than just time on the mat. This is the layer a muscle-worn wearable can add to a program built around Nordic curls: showing whether a given session actually produced high biceps femoris output, rather than assuming that performing the movement automatically delivered the eccentric loading the trials relied on. Surface EMG interpretation has real limits, amplitude reflects a mix of recruitment and length-tension effects and should not be read as a direct measure of tissue adaptation, but as one input into whether a session looks like the sessions that produced the outcomes above, it is a more direct signal than simply logging that the exercise was performed.

Key takeaways

• Adding Nordic hamstring curls to a training program is associated with roughly a 50 percent reduction in hamstring injury rates, replicated across meta-analyses and two large randomised controlled trials.

• The injury risk the exercise addresses is specific: eccentric knee flexor weakness and short biceps femoris fascicles, both independently linked to 4-fold or greater injury risk in prospective cohorts.

• The Nordic curl changes both eccentric strength and fascicle length, and EMG data show it drives higher biceps femoris activation than most alternative hamstring exercises.

• Volume is forgiving (both higher and lower weekly doses work), but compliance is not. Effects reported in the RCTs are compliance-dependent and degrade sharply with inconsistent dosing.

• Confirming a movement was performed is not the same as confirming it produced the loading associated with injury reduction.

References

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10. Goode AP, Reiman MP, Harris L, et al. Eccentric training for prevention of hamstring injuries may depend on intervention compliance: a systematic review and meta-analysis. Br J Sports Med. 2015;49(6):349-356.

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