REF-1794 · Ema et al., 2026 · Journal of Sports Sciences, · Paper · PubMed

Nordic hamstring training twice a week raised Nordic-specific eccentric strength more than once a week (d 0.50-0.77) over 6 weeks in 21 healthy men, while several general measures improved similarly in both with no group difference (isotonic power d −0.06); total impulse tracked adaptation better than total repetitions

Nordic strength measures, not injuries, in one small three-arm trial

Main caveat: Small: 21 men in three arms, about 7 per arm; legs analysed as units (42), which can overstate precision if the two legs of one person are treated as…
limited, mixed evidenceMeasured on non-athletes to trained athletesRead from the abstract only

Ema and colleagues asked how the amount of Nordic hamstring training relates to what it builds, and whether counting repetitions or total impulse (force summed over time across all sessions) describes the dose better. Twenty-one healthy men were randomised to bilateral Nordics twice a week, once a week, or no training for 6 weeks, with each leg analysed separately (42 legs).

Exercise-specific outcomes (Nordic peak torque, break-point angle, eccentric torque) and general outcomes (isometric torque, isotonic power, work in a fatigue task, jump height, muscle architecture and stiffness) were measured before and after. Both training groups improved every Nordic-specific measure, and twice weekly improved them more (d 0.50-0.77).

Several general measures improved by a similar amount in both training groups, isotonic power for example (d −0.06). Total impulse interacted with time for both specific and general outcomes, and biceps femoris stiffness fell more in the once-weekly group, which the authors read as a non-linear dose relationship for stiffness.

They conclude that total impulse quantifies the Nordic dose better than repetitions.

Participants

21 healthy men (42 legs), split across three arms; per-arm numbers, age, training background and sport are not in the abstract.

Protocol

TRA2: bilateral Nordics twice a week; TRA1: once a week; control: no Nordics; 6 weeks.
Sets, repetitions, progression and total repetitions per arm: not in the abstract.
Outcomes before and after: Nordic peak torque, break-point angle, eccentric torque; isometric torque, isotonic power, total work in a fatigue task, jump height, muscle architecture, muscle stiffness (biceps femoris among the muscles).
Analysis: group comparisons and linear mixed models with total impulse as a continuous covariate; legs as the unit.

Key Results

OutcomeResult
Nordic-specific measures (peak torque, break-point angle, eccentric torque)improved in both training groups; greater in TRA2 than TRA1, d = 0.50-0.77
General measures (e.g. isotonic power)several improved similarly in both training groups, no group difference; isotonic power d = −0.06
Time × total impulsesignificant interactions for both Nordic-specific and general outcomes
Biceps femoris stiffnesslarger reduction in TRA1 than TRA2
The abstract gives no values for the control group, no confidence intervals, and does not name which general measures did or did not improve beyond isotonic power.

Practical Application

Twice-weekly Nordics built more Nordic-specific eccentric strength than once weekly over 6 weeks (d 0.50-0.77), but several general measures, isotonic power among them, rose about as much on either frequency. Eccentric strength in healthy men in a small trial; it says nothing directly about hamstring injuries.
For the Nordic itself, two sessions a week did more than one; for several general measures, one did as well as two. Inference, not tested here: once a week may be enough where the aim is general hamstring and jump qualities; whether either frequency changes hamstring injury risk was not measured.
Count the work, not only the reps. Total impulse described the dose-response better than repetitions. Inference, not tested here: a slower, longer-held Nordic rep is more dose than a quick drop, so rep counts alone undercount it.
Partial tension with [SYNTH-59]. The guide keeps the Nordic in a sprinter's week and says a low volume kept up, on REF-887 (low and high volumes gave similar eccentric-strength gains across 13 studies).Here, on Nordic-specific eccentric strength, the outcome closest to REF-887's, doubling the weekly frequency gave larger gains (d 0.50-0.77), although once a week also improved it; REF-887 did not measure this trial's general outcomes, so nothing is confirmed there.One small trial in healthy men weighs less than a 13-study meta-analysis read in full; the guide's line stands with this tension stated. Injury protection rests on REF-766, not on this paper.
This is not injury treatment advice; a hamstring strain is assessed and rehabilitated with a physiotherapist or sports physician.

Limitations

Small: 21 men in three arms, about 7 per arm; legs analysed as units (42), which can overstate precision if the two legs of one person are treated as independent.
Healthy men of unstated training status; no women, no in-season athletes, no injury or sprint outcome.
Repetitions, sets and progression per arm are not in the abstract, so the dose cannot be copied.
Muscle architecture and stiffness are markers; the non-linear stiffness reading rests on one group difference.
Written from the abstract and the PubMed record; full text not read.
How this entry was checked and changed
Why this level

a parallel RCT with about 7 per arm (21 in three arms) read from the abstract, with key methods missing (per-arm numbers, sets and repetitions, effect intervals) and legs rather than people as the unit