If you want to get stronger at leg extensions, doing squats works just as well as doing leg extensions.
Scientific Claim
Back squat and leg extension training produce similar improvements in leg extension 3RM strength (+19.8% vs. +23.4%) in untrained young women after 8 weeks, with no statistically significant difference between groups.
Original Statement
“no between-group difference was observed in 3RM-LE increases (SQ = +19.8% vs. LE = +23.4%; p = 0.824).”
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 null result is clearly reported. 'Produce similar improvements' is appropriately stated as probabilistic due to potential measurement variability.
More Accurate Statement
“Back squat and leg extension training likely produce similar improvements in leg extension 3RM strength (+19.8% vs. +23.4%) in untrained young women after 8 weeks, with no statistically significant difference between groups.”
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 compound lower-body exercises consistently transfer to isolated leg extension strength gains.
Whether compound lower-body exercises consistently transfer to isolated leg extension strength gains.
What This Would Prove
Whether compound lower-body exercises consistently transfer to isolated leg extension strength gains.
Ideal Study Design
A meta-analysis of 15+ RCTs comparing compound (e.g., squats, leg press) vs. isolation (leg extension) training on 3RM leg extension strength, with standardized protocols and blinded assessors.
Limitation: Cannot determine if transfer is due to neural adaptation or muscle growth.
Randomized Controlled TrialLevel 1bIn EvidenceCausal equivalence of back squats and leg extensions for improving leg extension strength.
Causal equivalence of back squats and leg extensions for improving leg extension strength.
What This Would Prove
Causal equivalence of back squats and leg extensions for improving leg extension strength.
Ideal Study Design
A double-blind RCT of 120 untrained women aged 18–30, randomized to 8 weeks of back squats or leg extensions (3×8–12 RM, 2×/week), with 3RM leg extension tested by blinded assessors using standardized equipment.
Limitation: Does not assess whether this equivalence holds at higher intensities or longer durations.
Prospective Cohort StudyLevel 2bReal-world association between squat training and leg extension strength gains.
Real-world association between squat training and leg extension strength gains.
What This Would Prove
Real-world association between squat training and leg extension strength gains.
Ideal Study Design
A 1-year cohort of 300 untrained women tracking voluntary squat or leg extension training frequency and 3RM leg extension performance, adjusting for total leg volume and training experience.
Limitation: Cannot control for technique changes or motivation differences.
Evidence from Studies
Supporting (1)
Comparison of Muscle Hypertrophy and Strength Adaptations Induced by Back Squat and Leg Extension Resistance Exercises.
Both exercises—squats and leg extensions—made the women stronger at leg extensions by about the same amount, and the study proves there’s no real difference between them for that specific move.