The way your muscles fire when you do leg presses vs. leg extensions matches up with which muscles end up growing bigger after training.
Scientific Claim
Muscle excitation patterns during leg press and knee extension, as measured by surface electromyography, are associated with the observed differences in muscle hypertrophy after 12 weeks of training.
Original Statement
“A follow-up experiment using surface electromyography showed that muscle excitation patterns during KE and LP generally mirrored the between-condition hypertrophic differences and similarities observed after the training intervention.”
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 states that EMG patterns 'mirrored' hypertrophic outcomes, but does not establish causation or control for confounders. The verb 'mirrored' implies correspondence, not causation, but the claim is still overstated as a mechanistic link without direct causal testing.
More Accurate Statement
“Muscle excitation patterns during leg press and knee extension are associated with the observed differences in muscle hypertrophy after 12 weeks of training.”
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.
Randomized Controlled TrialLevel 1bWhether manipulating muscle activation during leg press and knee extension directly causes differential hypertrophy.
Whether manipulating muscle activation during leg press and knee extension directly causes differential hypertrophy.
What This Would Prove
Whether manipulating muscle activation during leg press and knee extension directly causes differential hypertrophy.
Ideal Study Design
A crossover RCT with 25+ untrained adults performing 12 weeks of leg press and knee extension under conditions that artificially alter EMG activation (e.g., biofeedback, neuromuscular electrical stimulation), with MRI-measured muscle volume changes in rectus femoris, vasti, gluteus maximus, and adductor magnus as primary outcomes.
Limitation: Cannot replicate natural movement patterns under altered activation.
Prospective Cohort StudyLevel 2bWhether individuals with higher EMG activation during leg press consistently show greater gluteus maximus hypertrophy over time.
Whether individuals with higher EMG activation during leg press consistently show greater gluteus maximus hypertrophy over time.
What This Would Prove
Whether individuals with higher EMG activation during leg press consistently show greater gluteus maximus hypertrophy over time.
Ideal Study Design
A 6-month prospective cohort study of 100+ adults performing leg press or knee extension, with baseline and monthly EMG and MRI measurements to correlate activation amplitude and duration with muscle volume changes.
Limitation: Cannot determine if activation drives growth or if growth alters activation.
Case-Control StudyLevel 2bWhether individuals with high vs. low rectus femoris EMG activation during KE show different hypertrophy responses.
Whether individuals with high vs. low rectus femoris EMG activation during KE show different hypertrophy responses.
What This Would Prove
Whether individuals with high vs. low rectus femoris EMG activation during KE show different hypertrophy responses.
Ideal Study Design
A case-control study comparing 20 adults with high vs. 20 with low rectus femoris EMG activation during KE training (matched for volume, intensity, duration), measuring 12-week hypertrophy via MRI.
Limitation: Cannot establish temporal sequence or rule out pre-existing differences.
Evidence from Studies
Supporting (1)
Hypertrophic Effects of Single- versus Multi-Joint Exercise: A Direct Comparison Between Knee Extension and Leg Press.
The study found that how much your muscles 'light up' during leg press vs. knee extension matches how much they grow afterward—so yes, the way your muscles fire during exercise is linked to how much they get bigger.