Squats make the outer thigh muscle bigger near the knee more than leg extensions do, but both exercises build it similarly higher up on the thigh.
Scientific Claim
In untrained young women, 8 weeks of Smith machine back squat training results in greater hypertrophy of the vastus lateralis at the distal site (+18.2%) compared to leg extension training (+11.2%), while no significant differences occur at proximal or middle sites.
Original Statement
“Conversely, the SQ showed greater increases in VL at the distal site (+18.2% vs. +11.2%; 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 RCT design supports causal inference, but lack of blinding and abstract-only access warrant cautious language. 'Results in' is appropriately softened to 'likely results in'.
More Accurate Statement
“In untrained young women, 8 weeks of Smith machine back squat training likely results in greater hypertrophy of the vastus lateralis at the distal site (+18.2%) compared to leg extension training (+11.2%), while no significant differences occur at proximal or middle sites.”
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 distal vastus lateralis hypertrophy than leg extensions across populations.
Whether back squats consistently produce greater distal vastus lateralis hypertrophy than leg extensions across populations.
What This Would Prove
Whether back squats consistently produce greater distal vastus lateralis hypertrophy than leg extensions across populations.
Ideal Study Design
A meta-analysis of 12+ RCTs comparing back squats and leg extensions in untrained young women, using standardized ultrasound to measure vastus lateralis thickness at proximal, middle, and distal sites, with identical training volume and intensity.
Limitation: Cannot control for individual biomechanical differences across studies.
Randomized Controlled TrialLevel 1bIn EvidenceCausal effect of back squat vs. leg extension on distal vastus lateralis growth.
Causal effect of back squat vs. leg extension on distal vastus lateralis growth.
What This Would Prove
Causal effect of back squat vs. leg extension on distal vastus lateralis growth.
Ideal Study Design
A double-blind, parallel-group RCT of 100 untrained women aged 18–30, randomized to 8 weeks of Smith machine back squat or leg extension training (3×8–12 RM, 2×/week), with blinded ultrasound measurements of vastus lateralis thickness at three sites.
Limitation: Limited to young, untrained women; results may not generalize to other demographics.
Prospective Cohort StudyLevel 2bLong-term association between squatting and distal vastus lateralis development in real-world training.
Long-term association between squatting and distal vastus lateralis development in real-world training.
What This Would Prove
Long-term association between squatting and distal vastus lateralis development in real-world training.
Ideal Study Design
A 1-year prospective cohort of 200 untrained women who choose either squats or leg extensions as their primary quad exercise, with monthly ultrasound measurements of vastus lateralis thickness and controlled for total weekly volume and nutrition.
Limitation: Self-selection bias may confound results due to preference or access to equipment.
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 Smith machine squats made the lower part of the thigh muscle grow more than leg extensions did, just like the claim said — and nowhere else on the muscle did it make a difference.