Does building bigger muscles really translate to getting stronger? This new 15-week training study indicates muscle growth is very strongly tied to strength gains—more than previously thought.
Overview
- What did they test? Researchers investigated how changes in muscle size and neuromuscular activation relate to strength gains after 15 weeks of lower-body resistance training. Using MRI for quadriceps volume, EMG for neural activation, and strength tests (isometric torque and 1RM), they applied within-participant correlations to track how changes in each individual’s muscle size related to their own strength gains over time.
- What did they find? Muscle growth was very strongly correlated with strength gains (r = 0.89–0.92), while neuromuscular activation showed only a moderate correlation (r = 0.56–0.58). Statistical models revealed that muscle growth was more than five times as influential as neuromuscular activation in explaining strength increases.
- What does it mean for you? This study highlights that tracking your own progress over time is more meaningful than comparing yourself to others. Your strength improvements appear highly tied to your own hypertrophy, even if others progress differently.
What’s The Problem?
Despite decades of research showing that bigger muscles tend to be stronger across individuals (e.g., muscle volume explaining ~60% of isometric strength variance) 1, studies tracking training-induced changes have reported only weak-to-moderate links between hypertrophy and strength 2 3. This has fueled debate about whether size gains meaningfully drive strength gains after resistance training 4 5. In my opinion, a lot of the confusion from past research comes down to methods of measurement and design.
Many studies used lower-resolution tools to measure muscle size instead of MRI, ran for only 8–12 weeks when neural adaptations often dominate, or relied on raw surface electromyography (EMG) signals that can be skewed by muscle growth itself (e.g., sEMG amplitude vs. M-wave–normalized EMG). Additionally, studies typically complete measurements before and after a training period once, which leaves more room for error as compared to collecting multiple measurements of the variable of interest. Crucially, most studies compare people against each other, reducing everyone’s progress to a single “percent change.” When studies compare people against each other, they take each person’s results and boil them down to a single “before vs. after” number (e.g., “Cody’s strength went up 15% and his muscle grew 8%”). Then they line up everyone’s percent changes and look for a correlation across the group. While this approach can be useful in certain contexts, it ignores the fact that Cody’s progress is tied to Cody’s own muscle growth, not to how he stacks up against James or Layne. Everyone’s baseline size, limb length, tendon leverage, and other fixed traits are different, so comparing percent changes between people can mask the true link between muscle growth and strength.
This new study from Marques and colleagues tracked each person’s own changes over time using repeated measures. By looking within individuals, the analysis is more sensitive and captures a more accurate relationship between muscle size and strength. With a longer training program, high-resolution MRI scans, repeated strength testing, and more precise EMG methods, the researchers could rigorously test how much muscle growth versus neural activation explained each person’s strength gains during lower-body resistance training. Let's see what they found.
Purpose
This study aimed to assess the intra-individual relationship between the changes in muscle volume and neuromuscular activation with the changes in strength (isometric and one repetition maximum lifting strength [1RM]) in male adults after a relatively prolonged 15 weeks (45 sessions) of resistance training (RT).
