Effects of Strength Training on Cognitive Function, Brain-Derived Neurotrophic Factor and Insulin-Like Growth Factor 1 in Highly-Trained Young Female Soccer Players
Sports medicine - open · 2026
Adding strength training helped teen female players get stronger, pass better and score higher on a Stroop test, but their BDNF and IGF-1 levels didn't move, so skip the 'rewires the brain' pitch.
The paper
RCT, n=22 highly-trained adolescent female soccer players (mean age 14.9), 11 per group, comparing 12 weeks of added strength training to an active soccer-only control.
What they found
Strength training produced large group-by-time effects on 1-RM bench press, lat pulldown and leg press (all p<0.001, ηp2=0.36-0.43), soccer passing performance on the LSPT (p=0.007, ηp2=0.22) and Stroop test performance (p<0.001, ηp2=0.56), but no change in serum BDNF or IGF-1 (p>0.05, ηp2=0.00-0.04).
Study design
Parallel-group RCT with an active control (not a no-treatment or placebo arm), n=22 total (11 vs 11), in youth (14-15yo) Tier 3 female soccer players over a single 12-week in-season block.
Methodology
Randomisation is stated but allocation concealment and assessor blinding are not described, and blinding of players to group assignment is impossible given the nature of the intervention, which leaves performance testing and the Stroop test open to expectation/performance bias. With only 11 per arm the study is underpowered for the biomarker outcomes (the null BDNF/IGF-1 result could be a true null or just noise), and five outcome domains were tested without a stated correction for multiple comparisons, inflating the chance that at least one 'significant' interaction is a false positive. Training volumes are described as matched but total loading was not equated (ST group did 2 ST + 3 soccer sessions vs 5 soccer sessions in controls), so the ST group is really being compared to a different overall training stimulus, not a pure add-on effect isolated from confounds like novelty or extra individualised coaching contact.
The appraisal
The strength and passing-performance gains are both statistically and plausibly clinically meaningful given the large effect sizes, and are consistent with well-established literature on resistance training dose-response in youth athletes. The LSPT result is actually strengthened by the fact the control group did more soccer-specific training volume yet showed no improvement, which argues against a simple retest or practice explanation for that finding. The Stroop improvement is more fragile: only the strength group improved, but since both arms repeated the same Stroop test, a pure test-familiarity effect should have shown in both, so 'practice effects' alone don't fully explain the result either. What's missing is the proposed mechanism, BDNF and IGF-1 were flat, so the 'training rewires the brain' story this paper is built around isn't supported by its own data. With only 11 players per arm, no stated assessor blinding, and roughly a dozen outcome comparisons run at p<0.05 without a correction, some findings, especially the Stroop result, could reflect chance, differential coach attention (Hawthorne effect) in the strength group, or motivation rather than a genuine training-cognition effect. Treat the strength and passing gains as reasonably solid; treat the cognitive result as an interesting signal, not a demonstrated effect.
The gap
Whether the Stroop improvement reflects a genuine training-induced cognitive adaptation or bias (differential coaching attention, motivation, or chance from multiple untested comparisons), since the biomarkers meant to explain the mechanism showed nothing. A larger, assessor-blinded trial with correction for multiple comparisons and follow-up beyond 12 weeks is needed before the cognitive claim, or any neuroplasticity mechanism, can be trusted.
Landmark context
This sits within the existing evidence base showing resistance training improves strength and soccer-specific performance in youth players (well established in prior S&C literature on adolescent female footballers), and extends the largely adult, mostly aerobic-exercise literature on exercise-induced neurotrophin change (e.g. BDNF response to endurance training) into a strength-training, youth, female-soccer context where the neurotrophin link has not been consistently replicated.
What to do Monday
Keep recommending 2x/week concurrent strength training (upper and lower body, 3x12 reps at 60-80% 1RM) layered onto in-season soccer training for highly-trained adolescent female players, provided total weekly training volume stays matched, the strength and LSPT passing gains here are reasonably solid and that part is actionable Monday. Do not market or justify the program to players or parents as boosting brain neurotrophic markers or 'rewiring the brain': this trial found no biomarker change, and the Stroop finding should be treated as hypothesis-generating, not proven. These results are specific to Tier 3/elite-caliber 14-15 year olds; don't extrapolate the passing or cognitive findings to recreational-level or younger players without direct evidence.
In practice
For the physio clinic: this is reassurance, not new information, that a modest 2x/week strength block during the competitive season is well tolerated and effective in adolescent female footballers, so if you're advising on athletic development or in-season loading for this population, matched-volume ST doesn't need to come at the expense of soccer-specific work. For the S&C floor: programme the structure used here (2 sessions/week, upper + lower, 3x12 reps @ 60-80% 1RM) with confidence for strength and likely passing-performance transfer, but leave the Stroop/BDNF result out of your athlete-facing pitch, it's not proven, and the biomarker data actively argue against a neuroplasticity mechanism. Caveat for both: this is one small trial (n=11/arm) in elite-caliber 14-15 year olds, so don't generalise the passing-transfer or cognitive claims to lower-tier, male, or younger athletes, and re-test strength with the same 1RM protocol rather than assuming gains persist beyond the 12-week window studied.
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