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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