In stiff-leg deadlifts, the size of the biceps femoris muscle (back of the thigh) seems to matter more for getting stronger at other exercises—unlike the other hamstring muscles.
Scientific Claim
The biceps femoris muscle shows a moderate positive correlation (r=0.6) with strength transfer in the stiff-leg deadlift group, suggesting it may play a unique role in hip-extension-oriented strength gains compared to other hamstring muscles.
Original Statement
“Finally, non-significant correlations were found between strength transfer and both whole and selective hamstring hypertrophy (r≤0.3), except for the BF in SDL (r=0.6).”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
probability
Can suggest probability/likelihood
Assessment Explanation
The authors correctly report this as an exception without overgeneralizing. The correlation is noted but not framed as causal, and the small sample size limits interpretation.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.
Randomized Controlled TrialLevel 1bWhether selectively increasing biceps femoris volume enhances strength transfer in hip-extension tasks.
Whether selectively increasing biceps femoris volume enhances strength transfer in hip-extension tasks.
What This Would Prove
Whether selectively increasing biceps femoris volume enhances strength transfer in hip-extension tasks.
Ideal Study Design
A double-blind RCT with 60 participants randomized to SDL training with or without targeted BF-focused overload (e.g., eccentric emphasis, specific loading), measuring BF volume via MRI and SDL/NHE 1RM transfer over 12 weeks.
Limitation: Cannot isolate whether the effect is due to hypertrophy or neural adaptation.
Prospective Cohort StudyLevel 2bWhether BF hypertrophy consistently predicts strength transfer in hip-dominant athletes over time.
Whether BF hypertrophy consistently predicts strength transfer in hip-dominant athletes over time.
What This Would Prove
Whether BF hypertrophy consistently predicts strength transfer in hip-dominant athletes over time.
Ideal Study Design
A 12-month prospective cohort of 100 powerlifters or sprinters performing SDL, with monthly BF volume measurements via MRI and biweekly strength transfer assessments to NHE.
Limitation: Cannot control for other training variables or recovery factors.
Cross-Sectional StudyLevel 3Whether elite athletes with high SDL performance show disproportionately large BF muscles.
Whether elite athletes with high SDL performance show disproportionately large BF muscles.
What This Would Prove
Whether elite athletes with high SDL performance show disproportionately large BF muscles.
Ideal Study Design
A cross-sectional analysis of 150 elite powerlifters and sprinters with documented SDL performance, comparing BF volume (MRI) to NHE strength transfer, controlling for total training volume and years of experience.
Limitation: Cannot determine if BF size causes performance or vice versa.
Evidence from Studies
Supporting (1)
The study found that when people did stiff-leg deadlifts, the biceps femoris muscle (a hamstring muscle) getting bigger was the only one linked to getting stronger in other exercises — which is exactly what the claim says.