If you want to get stronger at squats, doing squats is way better than doing leg extensions—but if you want to get stronger at leg extensions, both exercises work about the same.
Scientific Claim
Back squat training leads to greater improvements in back squat 3RM strength (+46.7%) compared to leg extension training (+21.3%) in untrained young women after 8 weeks, while both exercises produce similar gains in leg extension 3RM strength (+19.8% vs. +23.4%), suggesting strength gains are more specific to the trained movement pattern.
Original Statement
“Smith machine back squat induced greater increases in 3RM-SQ (+46.7 vs. 21.3%; p < 0.001), but 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
The RCT design supports causal claims, but the abstract does not confirm blinding or control of confounders. 'Leads to' should be softened to 'likely leads to' to reflect conservative interpretation.
More Accurate Statement
“Back squat training likely leads to greater improvements in back squat 3RM strength (+46.7%) compared to leg extension training (+21.3%) in untrained young women after 8 weeks, while both exercises likely produce similar gains in leg extension 3RM strength (+19.8% vs. +23.4%), suggesting strength gains are more specific to the trained movement pattern.”
Evidence from Studies
Supporting (1)
Comparison of Muscle Hypertrophy and Strength Adaptations Induced by Back Squat and Leg Extension Resistance Exercises.
People who did squats got much stronger at squats, but not necessarily at leg extensions, and people who did leg extensions got just as strong at leg extensions as the squatters did—so your body gets stronger at the exact exercise you practice.