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, correspond to 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' hypertrophic outcomes, but does not establish statistical correlation or control for confounders. Without explicit statistical analysis of EMG-hypertrophy relationships, this is an observational association.
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 manipulating muscle activation during leg press or knee extension directly alters hypertrophic outcomes.
Whether manipulating muscle activation during leg press or knee extension directly alters hypertrophic outcomes.
What This Would Prove
Whether manipulating muscle activation during leg press or knee extension directly alters hypertrophic outcomes.
Ideal Study Design
A crossover RCT with 40+ untrained adults performing leg press and knee extension under conditions that artificially enhance or suppress activation of rectus femoris (e.g., via biofeedback or neuromuscular electrical stimulation), with MRI-measured muscle volume changes as primary outcome, controlling for load and volume.
Limitation: Cannot isolate activation from mechanical tension or metabolic stress as the primary driver of hypertrophy.
Prospective Cohort StudyLevel 2bWhether baseline or training-induced changes in EMG amplitude predict future hypertrophy in specific quadriceps heads.
Whether baseline or training-induced changes in EMG amplitude predict future hypertrophy in specific quadriceps heads.
What This Would Prove
Whether baseline or training-induced changes in EMG amplitude predict future hypertrophy in specific quadriceps heads.
Ideal Study Design
A 12-week prospective cohort study measuring EMG amplitude during KE and LP in 100+ untrained adults, correlating average activation levels with MRI-measured muscle volume changes in each quadriceps head, controlling for training volume, diet, and baseline muscle size.
Limitation: Cannot determine if EMG differences cause hypertrophy or are merely correlated with other factors like movement technique.
Case-Control StudyLevel 2bWhether individuals with high vs. low rectus femoris activation during KE show different hypertrophic responses.
Whether individuals with high vs. low rectus femoris activation during KE show different hypertrophic responses.
What This Would Prove
Whether individuals with high vs. low rectus femoris activation during KE show different hypertrophic responses.
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 volume and baseline muscle size, measuring 12-week hypertrophy via MRI.
Limitation: Cannot establish causality; selection bias may influence group 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 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.