Previous Hamstring Injury Does Not Impact Biceps Femoris Long Head Fascicle Length and Eccentric Knee Flexion Strength Changes Following a Low-Volume Resistance Training Intervention in Elite Under-20-Year-Old Male Gaelic Footballers
European journal of sport science · 2026
A small, uncontrolled 9-week Nordic/RDL study in youth Gaelic footballers found modest fascicle-length gains but no strength gains, and was too underpowered to say whether prior hamstring injury blunts adaptation.
The paper
Prospective cohort/intervention study, n=26 elite U20 male Gaelic footballers (10 with prior hamstring injury in past 12 months, 16 without), single-arm 9-week NHE+RDL programme.
What they found
BFlh fascicle length increased significantly over 9 weeks (β = 0.31 cm, SE = 0.15 cm, p = 0.04) with no significant time*limb-type interaction; eccentric knee flexion strength did not significantly change (β = 9.53 N, SE = 12.97 N, p = 0.47), again with no significant interaction by prior-injury status.
The appraisal
This is a small, uncontrolled single-arm design (no non-training comparison group), so the fascicle length change cannot be cleanly attributed to the intervention versus normal in-season adaptation or measurement variability. The fascicle length effect is barely significant (p = 0.04) with a wide SE relative to the estimate, and 0.31 cm is a modest absolute change against typical measurement error (~0.2-0.4 cm) for ultrasound fascicle length, its clinical meaningfulness is doubtful. The strength outcome was clearly null. With only 10 previously-injured limbs, the study is underpowered to detect anything but a large interaction effect, so 'no difference between limb types' is an absence-of-evidence finding, not evidence of equivalence.
The gap
No control/comparison arm and a very small previously-injured subgroup (n=10) mean this can't distinguish a true intervention effect from natural adaptation, and it can't rule out a clinically important between-limb difference that the study was simply too small to detect.
Landmark context
This sits downstream of the archetypal NHE/BFlh fascicle-lengthening literature (e.g. work by Bourne, Timmins, and Opar establishing NHE-induced fascicle lengthening as a hamstring-injury risk-reduction mechanism) and the broader eccentric-strength-asymmetry literature following prior hamstring injury; this paper's contribution is narrowly testing whether previous injury blunts the expected adaptation, and finds no signal for that, a null/negative extension rather than a contradiction of the foundational work.
What to do Monday
Does not change practice: it does not challenge continuing standard NHE-based hamstring programming for previously injured athletes, but clinicians should not read this as reassurance that previously injured hamstrings adapt identically to training, the study is too small and uncontrolled to support that conclusion either way.
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