If you want to grow the front part of your thigh muscle (rectus femoris), doing leg extensions might work better than doing leg presses.
Scientific Claim
In resistance-trained individuals, single-joint exercises like leg extensions are more likely to promote greater hypertrophy of the rectus femoris region of the quadriceps compared to multi-joint exercises like leg press, based on 8 weeks of training with posterior probabilities of 0.910–0.990.
Original Statement
“Point estimates for the rectus femoris outcomes favored the single-joint exercise intervention with posterior probabilities ranging from 0.910 ≤ P ≤ 0.990.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
probability
Can suggest probability/likelihood
Assessment Explanation
The study is an RCT with randomization and control, supporting causal inference, but Bayesian probabilities are probabilistic, not definitive. The use of 'more likely' aligns with recommended verb strength.
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 extensions consistently produce greater rectus femoris hypertrophy than leg press across diverse populations and protocols.
Whether leg extensions consistently produce greater rectus femoris hypertrophy than leg press across diverse populations and protocols.
What This Would Prove
Whether leg extensions consistently produce greater rectus femoris hypertrophy than leg press across diverse populations and protocols.
Ideal Study Design
A meta-analysis of 15+ high-quality RCTs (n≥50 per trial) comparing leg extensions vs. leg press in resistance-trained adults (age 18–40), using MRI-measured rectus femoris muscle thickness as primary outcome, with standardized volume, intensity, and duration (8–12 weeks).
Limitation: Cannot establish mechanisms or account for individual variability in muscle fiber composition.
Randomized Controlled TrialLevel 1bIn EvidenceCausal effect of leg extension vs. leg press on rectus femoris growth under controlled conditions.
Causal effect of leg extension vs. leg press on rectus femoris growth under controlled conditions.
What This Would Prove
Causal effect of leg extension vs. leg press on rectus femoris 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 extensions or leg press (3x/week, 3–4 sets, 8–12 reps, 70–80% 1RM), with MRI-measured rectus femoris 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 extension use and rectus femoris size in real-world training environments.
Long-term association between habitual leg extension use and rectus femoris size in real-world training environments.
What This Would Prove
Long-term association between habitual leg extension use and rectus femoris size in real-world training environments.
Ideal Study Design
A 2-year prospective cohort tracking 200 resistance-trained individuals who self-select leg extensions or leg press as primary quad exercise, measuring rectus femoris 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 when people who already lift weights do leg extensions (a single-knee movement), their front thigh muscle (rectus femoris) grows more than when they do leg presses (a multi-joint movement), just like the claim said.