When untrained men get stronger during dynamic leg movements like standing up, the biggest factor is how much their thigh muscles fire, especially when combined with changes in the deep thigh muscle’s fiber angle and overall muscle size.
Scientific Claim
In previously untrained men, changes in concentric and eccentric knee extension strength after 10 weeks of heavy resistance training are most strongly associated with increases in average quadriceps muscle activation (EMG:M) combined with changes in vastus intermedius fascicle angle and proximal quadriceps cross-sectional area, explaining 40–41% of variability in strength gains.
Original Statement
“The models best predicting the change in concentric and eccentric torque both included the combination of the change in quadriceps (i.e., mean of all muscles) EMG:M and the change in vastus intermedius fascicle angle combined with either a change in proximal-region VL (R2 = 0.40, p < 0.001) or whole quadriceps (R2 = 0.41, p < 0.001) CSA”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The study design is observational and lacks intervention manipulation, so causation cannot be claimed. The use of 'associated with' and reporting of R² and AICc values correctly reflects correlational 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.
Randomized Controlled TrialLevel 1bThat enhancing quadriceps activation and VI fascicle angle specifically causes greater concentric/eccentric strength gains than training without targeting these factors.
That enhancing quadriceps activation and VI fascicle angle specifically causes greater concentric/eccentric strength gains than training without targeting these factors.
What This Would Prove
That enhancing quadriceps activation and VI fascicle angle specifically causes greater concentric/eccentric strength gains than training without targeting these factors.
Ideal Study Design
A double-blind RCT of 120+ untrained men aged 18–40, randomized to standard heavy resistance training vs. training with biofeedback to maximize quadriceps EMG:M and exercises targeting VI pennation (e.g., seated knee extensions with isometric holds), measuring EMG:M, VI fascicle angle via ultrasound, and isokinetic torque at 60°/s over 10 weeks.
Limitation: Cannot isolate whether VI fascicle angle changes are a result of training or a pre-existing trait.
Longitudinal Cohort StudyLevel 2bIn EvidenceWhether increases in quadriceps EMG:M and VI fascicle angle consistently predict dynamic strength gains across individuals during training.
Whether increases in quadriceps EMG:M and VI fascicle angle consistently predict dynamic strength gains across individuals during training.
What This Would Prove
Whether increases in quadriceps EMG:M and VI fascicle angle consistently predict dynamic strength gains across individuals during training.
Ideal Study Design
A prospective cohort of 250+ untrained adults (18–45) undergoing 10 weeks of standardized heavy resistance training, with weekly EMG:M (M-wave normalized), VI fascicle angle, and proximal CSA measurements, and biweekly concentric/eccentric torque assessments.
Limitation: Cannot determine if activation changes are due to neural adaptation or reduced inhibition.
Cross-Sectional StudyLevel 3Whether individuals with higher baseline quadriceps EMG:M and VI fascicle angle demonstrate greater dynamic strength capacity.
Whether individuals with higher baseline quadriceps EMG:M and VI fascicle angle demonstrate greater dynamic strength capacity.
What This Would Prove
Whether individuals with higher baseline quadriceps EMG:M and VI fascicle angle demonstrate greater dynamic strength capacity.
Ideal Study Design
A cross-sectional analysis of 300+ healthy adults aged 20–50 with varying training histories, measuring quadriceps EMG:M, VI fascicle angle, proximal CSA, and isokinetic torque at 60°/s, controlling for age, sex, and body composition.
Limitation: Cannot determine if observed associations are causal or due to selection bias.
Evidence from Studies
Supporting (1)
The study found that when untrained men did heavy leg workouts for 10 weeks, the main reasons their knee strength improved were because their thigh muscles fired more strongly and their muscle fibers changed angle and size — just like the claim said.