Leg presses make your butt and inner thigh muscles bigger, but leg extensions don’t — if you want to grow those muscles, leg presses are the better choice.
Scientific Claim
In untrained adults, leg press training is associated with significant hypertrophy of the gluteus maximus (+15.4%) and adductor magnus (+6.2%) after 12 weeks of training at 70% one-repetition maximum, twice weekly, while knee extension does not produce similar changes in these muscles.
Original Statement
“LP, but not KE, increased volumes of the gluteus maximus (+15.4%) and the adductor magnus (+6.2%) (P ≤ 0.001).”
Evidence Quality Assessment
Claim Status
overstated
Study Design Support
Design cannot support claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The abstract does not confirm randomization or control for confounders. The verb 'increases' implies causation, but only association can be claimed. The effect is specific to untrained adults under this protocol.
More Accurate Statement
“In untrained adults, leg press training is associated with significant hypertrophy of the gluteus maximus (+15.4%) and adductor magnus (+6.2%) after 12 weeks of training at 70% one-repetition maximum, twice weekly, while knee extension is not associated with similar changes in these muscles.”
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 leg press consistently induces greater gluteus maximus and adductor magnus hypertrophy than single-joint exercises across populations and protocols.
Whether leg press consistently induces greater gluteus maximus and adductor magnus hypertrophy than single-joint exercises across populations and protocols.
What This Would Prove
Whether leg press consistently induces greater gluteus maximus and adductor magnus hypertrophy than single-joint exercises across populations and protocols.
Ideal Study Design
A meta-analysis of all RCTs comparing gluteus maximus and adductor magnus hypertrophy via MRI after leg press vs. single-joint exercises (e.g., hip thrust, adductor machine) in untrained adults, using standardized protocols (70% 1RM, 5×10, 2x/week, 10–16 weeks), with controlled nutrition and activity.
Limitation: Cannot determine if the effect is due to mechanical load or joint angle specificity.
Randomized Controlled TrialLevel 1bWhether leg press causally induces greater hypertrophy in gluteus maximus and adductor magnus than knee extension.
Whether leg press causally induces greater hypertrophy in gluteus maximus and adductor magnus than knee extension.
What This Would Prove
Whether leg press causally induces greater hypertrophy in gluteus maximus and adductor magnus than knee extension.
Ideal Study Design
A double-blind, randomized crossover RCT with 40+ untrained adults, each performing 12 weeks of leg press and knee extension (70% 1RM, 5×10, 2x/week) in random order, with MRI-measured gluteus maximus and adductor magnus volume as primary outcomes, and EMG to confirm activation patterns.
Limitation: Cannot determine if the effect is maintained after training cessation or in trained individuals.
Prospective Cohort StudyLevel 2bWhether individuals who regularly use leg press in real-world settings develop larger gluteus maximus and adductor magnus over time compared to those who use only single-joint exercises.
Whether individuals who regularly use leg press in real-world settings develop larger gluteus maximus and adductor magnus over time compared to those who use only single-joint exercises.
What This Would Prove
Whether individuals who regularly use leg press in real-world settings develop larger gluteus maximus and adductor magnus over time compared to those who use only single-joint exercises.
Ideal Study Design
A 2-year prospective cohort study of 150+ gym-goers who self-select leg press or knee extension as their primary lower-body exercise, with annual MRI scans of gluteus maximus and adductor magnus volume, controlling for total training volume, nutrition, and other exercises.
Limitation: Cannot rule out selection bias or confounding from other compound movements.
Evidence from Studies
Supporting (1)
Hypertrophic Effects of Single- versus Multi-Joint Exercise: A Direct Comparison Between Knee Extension and Leg Press.
This study found that doing leg presses made the butt and inner thigh muscles grow bigger, but doing knee extensions didn’t — just like the claim said.