Different leg exercises make different parts of your thigh muscles bigger — leg extensions grow the front part, squats grow the lower outer part.
Scientific Claim
Leg extension exercises produce greater hypertrophy in the rectus femoris, while back squats produce greater hypertrophy in the distal vastus lateralis, indicating that exercise selection can target specific regions of the quadriceps muscle group in untrained young women.
Original Statement
“Based on our results, the leg extension induce greater rectus femoris hypertrophy, while the back squat promotes greater vastus lateralis hypertrophy, particularly at the distal site.”
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, and the conclusion synthesizes multiple significant findings. 'Can target' is appropriately probabilistic given blinding limitations.
More Accurate Statement
“Leg extension exercises likely produce greater hypertrophy in the rectus femoris, while back squats likely produce greater hypertrophy in the distal vastus lateralis, indicating that exercise selection can target specific regions of the quadriceps muscle group in untrained young women.”
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 exercise selection consistently produces regional quadriceps hypertrophy differences across populations.
Whether exercise selection consistently produces regional quadriceps hypertrophy differences across populations.
What This Would Prove
Whether exercise selection consistently produces regional quadriceps hypertrophy differences across populations.
Ideal Study Design
A meta-analysis of 20+ RCTs comparing compound vs. isolation leg exercises, using standardized ultrasound to measure rectus femoris and vastus lateralis hypertrophy at proximal, middle, and distal sites after 8–12 weeks of training.
Limitation: Cannot determine mechanisms (e.g., mechanical tension vs. metabolic stress) driving regional differences.
Randomized Controlled TrialLevel 1bIn EvidenceCausal effect of exercise selection on regional quadriceps hypertrophy.
Causal effect of exercise selection on regional quadriceps hypertrophy.
What This Would Prove
Causal effect of exercise selection on regional quadriceps hypertrophy.
Ideal Study Design
A double-blind RCT of 150 untrained women aged 18–30, randomized to leg extensions, back squats, or control, with ultrasound measurements of all three quadriceps sites at baseline and post-intervention, controlling for volume and intensity.
Limitation: Does not assess whether these differences persist beyond 8 weeks or translate to functional outcomes.
Prospective Cohort StudyLevel 2bAssociation between preferred leg exercise and regional quadriceps growth in real-world settings.
Association between preferred leg exercise and regional quadriceps growth in real-world settings.
What This Would Prove
Association between preferred leg exercise and regional quadriceps growth in real-world settings.
Ideal Study Design
A 1-year cohort of 500 untrained women tracking their primary leg exercise (squats, leg extensions, leg press) and quarterly ultrasound measurements of quadriceps regional thickness, adjusting for training volume and nutrition.
Limitation: Cannot control for self-selection bias or technique quality.
Evidence from Studies
Supporting (1)
Comparison of Muscle Hypertrophy and Strength Adaptations Induced by Back Squat and Leg Extension Resistance Exercises.
This study found that leg extensions make the front thigh muscle (rectus femoris) grow more, while squats make the lower outer part of the thigh muscle (distal vastus lateralis) grow more — so yes, different exercises can target different parts of the same muscle group.