Ever wonder if your latest PR is thanks to bigger muscles or just your brain getting better at lifting? It’s the classic 'neural vs. muscular' debate, and for good reason—both play a huge role. But which one is driving the bus?
A massive new 2025 meta-analysis published in Scientific Reports just gave us some of the clearest answers yet. Researchers pooled the data from 24 different randomized controlled trials to get a high-level view of how strength training really works. They looked at everything from raw strength increases to muscle growth, fiber type changes, and neural drive.
Let's break down what they found and what it means for your training.
The Big Picture: Yes, Lifting Makes You Stronger
No surprises here. The first major finding was that resistance training flat-out works. The analysis confirmed that structured lifting leads to significant, moderate-to-large increases in maximal strength (Standardized Mean Difference or SMD = 0.77).
When broken down by lift, the effects were even clearer:
- Squat Strength: Showed a large increase (SMD = 1.14).
- Bench Press Strength: Showed a moderate increase (SMD = 0.6).
This confirms what we know from experience, but it's the how that gets interesting.
The Neural Drive: Your Brain's Software Upgrade
A huge piece of the strength puzzle is neural adaptation. Think of it as your brain getting better at using the muscle you already have. The researchers found that strength training significantly boosts muscle activation, measured by electromyography (EMG), with a moderate effect size (SMD = 0.54).
In simple terms, your nervous system gets much more efficient at:
- Recruiting more motor units.
- Increasing the firing rate of those motor units.
- Improving coordination between muscles.
This neural upgrade was significant for both the upper and lower body. It's a powerful reminder that strength isn't just a physical trait; it's a skill. Your brain is learning to produce more force.
The Hypertrophy Factor: Size Does Matter (Mostly)
Of course, getting bigger helps you get stronger. The study confirmed that resistance training leads to a small but statistically significant increase in muscle thickness (SMD = 0.28).
But when they looked at specific muscles, the results were fascinating:
- Pectoralis Major (Chest): Showed the largest growth by far (SMD = 1.39).
- Triceps and Biceps: Also grew significantly (SMD = 0.65 and 0.61, respectively).
- Quadriceps: Here's where it gets weird. The rectus femoris (a central quad muscle) showed a moderate increase in thickness (SMD = 0.61). In contrast, the vastus lateralis (the outer quad sweep) did not show a statistically significant increase in thickness across the studies analyzed.
This highlights that hypertrophy responses can be muscle-specific, even within the same muscle group. Your exercise selection really matters for balanced development.
The Muscle Fiber Mystery
We often hear that heavy training shifts fast-twitch fibers from Type IIx (very powerful, but fatigue quickly) to Type IIa (still powerful, but more fatigue-resistant). This is thought to be a key adaptation for strength.
This meta-analysis looked for that exact shift. While they saw a trend in that direction—a slight decrease in Type IIx fibers and slight increases in Type I and Type IIa fibers—none of these changes were statistically significant.
This doesn't mean fiber type shifts don't happen, but it does suggest they weren't a primary, consistent driver of strength gains across these 24 studies. The neural and overall hypertrophy changes appear to be more impactful.
Do "Newbie Gains" Win? Not So Fast.
This is one of the most encouraging findings for long-term lifters. The study compared lifters with previous training experience to those without.
While the novices made great progress (SMD = 0.64), the experienced lifters actually saw a larger overall strength increase (SMD = 0.89 after researchers removed one outlier study).
This is fantastic news for anyone past the beginner stage. Even if you've been training for years, your body can still make powerful adaptations. You are not tapped out.
What This Means For Your Training
This research provides some clear, actionable takeaways for lifters and coaches:
- Strength is a Skill: The significant improvements in EMG show that getting stronger is about teaching your nervous system. Practice your main lifts with excellent form to maximize this neural learning.
- Lower Body May Adapt Faster: The analysis consistently found that the lower body got stronger and produced more torque than the upper body. It's normal for your squat to progress faster than your bench.
- Don't Assume Uniform Growth: Just because you're squatting doesn't mean all heads of the quad are growing equally. Use a variety of exercises to ensure you're developing muscles completely.
- Focus on the Big Rocks: Worry less about chasing specific muscle fiber changes and more about the proven drivers of strength: consistent progressive overload, getting bigger, and practicing the skill of lifting heavy.
- Keep Going: Experienced lifters are far from their potential. The data shows that even seasoned athletes can make massive strength gains.
The Bottom Line
Getting brutally strong is a two-part story. Your nervous system learns to be more efficient, and your muscles get bigger. This massive review confirms both are at play, with neural adaptations being a particularly powerful driver.
For lifters and coaches, the message is clear: focus on consistent, progressive overload in your key lifts to drive both neural and muscular adaptations. The gains will follow, whether you're a rookie or a seasoned veteran.
Reference:
Rong, W., Geok, S.K., Samsudin, S. et al. (2025). Effects of strength training on neuromuscular adaptations in the development of maximal strength: a systematic review and meta-analysis. Scientific Reports. https://pubmed.ncbi.nlm.nih.gov/40456806/