If you want to get stronger at squats, doing squats makes you way stronger than doing leg extensions.
Scientific Claim
Back squat training results in greater improvements in back squat 3RM strength (+46.7%) compared to leg extension training (+21.3%) in untrained young women after 8 weeks.
Original Statement
“Smith machine back squat induced greater increases in 3RM-SQ (+46.7 vs. 21.3%; 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
RCT design supports causal inference, but lack of blinding may inflate strength gains due to motivation or technique bias. 'Results in' is appropriately qualified as probabilistic.
More Accurate Statement
“Back squat training likely results in greater improvements in back squat 3RM strength (+46.7%) compared to leg extension training (+21.3%) in untrained young women after 8 weeks.”
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 back squats consistently produce greater squat strength gains than leg extensions across populations and training volumes.
Whether back squats consistently produce greater squat strength gains than leg extensions across populations and training volumes.
What This Would Prove
Whether back squats consistently produce greater squat strength gains than leg extensions across populations and training volumes.
Ideal Study Design
A meta-analysis of 20+ RCTs comparing squat vs. leg extension training in untrained adults, measuring 3RM squat strength after 6–12 weeks of matched volume and intensity, with blinded assessors.
Limitation: Cannot isolate whether gains are due to neural adaptation, muscle growth, or technique improvement.
Randomized Controlled TrialLevel 1bIn EvidenceCausal effect of back squats on squat-specific strength gains.
Causal effect of back squats on squat-specific strength gains.
What This Would Prove
Causal effect of back squats on squat-specific strength gains.
Ideal Study Design
A double-blind RCT of 150 untrained women aged 18–30, randomized to 8 weeks of back squats or leg extensions (3×8–12 RM, 2×/week), with 3RM squat tested by blinded strength coaches using standardized protocols.
Limitation: Does not assess transfer to other movements or long-term strength retention.
Prospective Cohort StudyLevel 2bAssociation between squat training frequency and squat strength gains in natural settings.
Association between squat training frequency and squat strength gains in natural settings.
What This Would Prove
Association between squat training frequency and squat strength gains in natural settings.
Ideal Study Design
A 1-year cohort of 400 untrained women tracking voluntary squat training frequency and 3RM squat performance, adjusting for total leg training volume, nutrition, and sleep.
Limitation: Cannot control for self-selection, technique quality, or motivation differences.
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 people who did back squats got much stronger at back squats, while people who did leg extensions didn’t get nearly as strong at back squats — exactly what the claim says.