Doing leg extensions makes the front thigh muscle bigger along its whole length more than doing squats, especially near the knee.
Scientific Claim
Leg extension exercises lead to greater hypertrophy of the rectus femoris muscle at proximal, middle, and distal sites in untrained young women after 8 weeks of training, with increases of 11.4%, 12.3%, and 17.5% respectively, compared to 2.0%, 5.7%, and 7.9% with back squats.
Original Statement
“The LE experienced greater increases in the 3 RF sites (proximal: +11.4% vs. +2.0%; middle: +12.3% vs. +5.7%; distal: 17.5% vs. +7.9%; all p < 0.001).”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
probability
Can suggest probability/likelihood
Assessment Explanation
The study is an RCT with randomization, permitting causal language, but blinding is unknown, so confidence is reduced. 'Lead to' is appropriately qualified as probabilistic given potential performance bias.
More Accurate Statement
“Leg extension exercises likely lead to greater hypertrophy of the rectus femoris muscle at proximal, middle, and distal sites in untrained young women after 8 weeks of training, with increases of 11.4%, 12.3%, and 17.5% respectively, compared to 2.0%, 5.7%, and 7.9% with back squats.”
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.
Systematic Review & Meta-AnalysisLevel 1aWhether leg extensions consistently produce greater rectus femoris hypertrophy than squats across diverse populations and training protocols.
Whether leg extensions consistently produce greater rectus femoris hypertrophy than squats across diverse populations and training protocols.
What This Would Prove
Whether leg extensions consistently produce greater rectus femoris hypertrophy than squats across diverse populations and training protocols.
Ideal Study Design
A meta-analysis of 15+ RCTs comparing leg extensions vs. back squats in untrained adults aged 18–35, using standardized ultrasound measurements of rectus femoris thickness at proximal, middle, and distal sites after 8–12 weeks of 2–3 sessions/week at 8–12 RM, with blinding of assessors and control for volume and intensity.
Limitation: Cannot establish causation in individual studies, only summarize existing evidence.
Randomized Controlled TrialLevel 1bIn EvidenceCausal effect of leg extensions vs. squats on rectus femoris hypertrophy with blinded outcome assessment.
Causal effect of leg extensions vs. squats on rectus femoris hypertrophy with blinded outcome assessment.
What This Would Prove
Causal effect of leg extensions vs. squats on rectus femoris hypertrophy with blinded outcome assessment.
Ideal Study Design
A double-blind RCT of 100 untrained young women (18–30 years), randomized to 8 weeks of leg extensions or back squats (3 sets × 8–12 RM, 2×/week), with ultrasound measurements of rectus femoris thickness at three sites by blinded technicians, controlling for diet and activity.
Limitation: Cannot prove long-term effects beyond 8 weeks or generalizability to other populations.
Prospective Cohort StudyLevel 2bLong-term association between leg extension training and rectus femoris growth in real-world settings.
Long-term association between leg extension training and rectus femoris growth in real-world settings.
What This Would Prove
Long-term association between leg extension training and rectus femoris growth in real-world settings.
Ideal Study Design
A 1-year prospective cohort of 200 untrained women tracking voluntary leg extension vs. squat use in gyms, with quarterly ultrasound measurements of rectus femoris thickness, adjusting for total training volume and nutrition.
Limitation: Cannot control for confounding variables like adherence or diet.
Evidence from Studies
Supporting (1)
Comparison of Muscle Hypertrophy and Strength Adaptations Induced by Back Squat and Leg Extension Resistance Exercises.
The study found that doing leg extensions made the front thigh muscle grow more than doing squats, exactly as the claim says — with the same numbers and in the same group of women.