The way your muscles fire when you do leg presses vs. leg extensions matches up with which muscles end up getting bigger after training.
Scientific Claim
Muscle excitation patterns during leg press and knee extension, as measured by surface electromyography, mirror the observed differences in muscle hypertrophy after 12 weeks of training in untrained adults.
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' hypertrophy, but does not confirm statistical testing or control for confounders. Without full methodological details, this is an observed association, not a proven mechanism.
More Accurate Statement
“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 in untrained adults.”
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 altered muscle activation during exercise causally drives differential hypertrophy in specific muscles.
Whether altered muscle activation during exercise causally drives differential hypertrophy in specific muscles.
What This Would Prove
Whether altered muscle activation during exercise causally drives differential hypertrophy in specific muscles.
Ideal Study Design
A double-blind RCT with 40+ untrained adults, randomized to either standard KE/LP or modified versions designed to selectively increase/decrease EMG activity in rectus femoris or gluteus maximus (e.g., via foot placement or resistance bands), with pre/post MRI and EMG to test if activation changes predict hypertrophy changes.
Limitation: Cannot isolate EMG from mechanical tension or metabolic stress as the primary driver.
Prospective Cohort StudyLevel 2bWhether individuals with higher EMG activation in a muscle during training consistently show greater hypertrophy over time.
Whether individuals with higher EMG activation in a muscle during training consistently show greater hypertrophy over time.
What This Would Prove
Whether individuals with higher EMG activation in a muscle during training consistently show greater hypertrophy over time.
Ideal Study Design
A 16-week prospective cohort of 100+ resistance-trained adults performing standardized leg press and KE, with continuous EMG monitoring during each session and weekly MRI scans to correlate average EMG amplitude with muscle volume change.
Limitation: Cannot control for individual variability in recovery, nutrition, or technique.
Case-Control StudyLevel 2bWhether individuals with high vs. low rectus femoris EMG activation during KE show different hypertrophy outcomes.
Whether individuals with high vs. low rectus femoris EMG activation during KE show different hypertrophy outcomes.
What This Would Prove
Whether individuals with high vs. low rectus femoris EMG activation during KE show different hypertrophy outcomes.
Ideal Study Design
A case-control study comparing 20 'high-activators' and 20 'low-activators' of rectus femoris during KE (based on EMG), matched for training history, volume, and diet, with pre/post MRI of quadriceps muscle volumes.
Limitation: Cannot establish direction of causality — does activation drive growth, or does growth alter activation?
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 each muscle 'lights up' during leg press and knee extension matches how much each muscle grows after 12 weeks of training — so yes, the muscle activity patterns predict the growth patterns.