If you want to grow the outer part of your thigh (vastus lateralis), leg presses might be more effective than leg extensions.
Scientific Claim
In resistance-trained individuals, multi-joint exercises like leg press are more likely to promote greater hypertrophy of the vastus lateralis region of the quadriceps compared to single-joint exercises like leg extensions, based on 8 weeks of training with posterior probabilities of 0.875–0.994.
Original Statement
“In contrast, point estimates for the vastus lateralis outcomes favored the multi-joint exercise intervention with posterior probabilities ranging from 0.875 ≤ P ≤ 0.994.”
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 Bayesian probabilities reflect likelihood, not certainty. 'More likely' appropriately reflects the probabilistic nature of the evidence.
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 produces greater vastus lateralis hypertrophy than leg extension across populations and protocols.
Whether leg press consistently produces greater vastus lateralis hypertrophy than leg extension across populations and protocols.
What This Would Prove
Whether leg press consistently produces greater vastus lateralis hypertrophy than leg extension across populations and protocols.
Ideal Study Design
A meta-analysis of 15+ RCTs (n≥50 per trial) comparing leg press vs. leg extension in resistance-trained adults (age 18–40), using MRI-measured vastus lateralis thickness as primary outcome, with standardized volume, intensity, and duration (8–12 weeks).
Limitation: Cannot determine if differences are due to joint angle, muscle activation, or mechanical tension.
Randomized Controlled TrialLevel 1bIn EvidenceCausal effect of leg press vs. leg extension on vastus lateralis growth under controlled conditions.
Causal effect of leg press vs. leg extension on vastus lateralis growth under controlled conditions.
What This Would Prove
Causal effect of leg press vs. leg extension on vastus lateralis growth under controlled conditions.
Ideal Study Design
A double-blind, crossover RCT with 40 resistance-trained adults (age 20–35), randomized to 8 weeks of leg press or leg extension (3x/week, 3–4 sets, 8–12 reps, 70–80% 1RM), with MRI-measured vastus lateralis thickness as primary outcome and contralateral leg as within-subject control.
Limitation: Cannot eliminate all performance bias without blinding of exercise type.
Prospective Cohort StudyLevel 2bLong-term association between habitual leg press use and vastus lateralis size in real-world training environments.
Long-term association between habitual leg press use and vastus lateralis size in real-world training environments.
What This Would Prove
Long-term association between habitual leg press use and vastus lateralis size in real-world training environments.
Ideal Study Design
A 2-year prospective cohort tracking 200 resistance-trained individuals who self-select leg press or leg extension as primary quad exercise, measuring vastus lateralis thickness via ultrasound every 6 months while controlling for total volume and diet.
Limitation: Cannot control for confounding variables like training history or nutrition.
Evidence from Studies
Supporting (1)
Exercise Selection Differentially Influences Lower Body Regional Muscle Development
This study found that doing leg presses (which use multiple joints) made the outer part of the thigh muscle grow more than doing leg extensions (which only bend the knee), just like the claim said.