Sarcoplasmic vs Myofibrillar Hypertrophy: What Science Actually Says
2026-02-16
You've probably heard it in every gym: "Bodybuilders are bigger but weaker because they train for sarcoplasmic hypertrophy, bro." It's one of fitness's most persistent myths—but what does the science actually say?
The Two Types of Muscle Growth (Theory)
Myofibrillar hypertrophy is the growth of the contractile apparatus—the actual muscle fibers (myofibrils) that generate force. Think of these as the motors inside your muscle cells. Sarcoplasmic hypertrophy theoretically refers to growth of the sarcoplasm (the fluid and non-contractile components surrounding the myofibrils)—glycogen stores, mitochondria, enzymes, and sarcoplasmic proteins.The claim: High-rep "pump" training increases sarcoplasm (making muscles bigger but not stronger), while heavy lifting builds myofibrils (making muscles stronger but not as big).
What 2025 Research Actually Shows
A November 2025 study published in Sport Sciences for Health directly compared heavy load (myofibrillar) vs. high repetition (sarcoplasmic) training protocols. The results? Both produced significant hypertrophy, but with nuanced differences in where the growth occurred.
The prevailing scientific consensus has shifted:
- Sarcoplasmic hypertrophy DOES happen — but probably not in the way the "bro scientists" describe it
- It's not just glycogen storage — research shows the sarcoplasm expands through increased sarcoplasmic protein content, not just fluid
- It may be a consequence, not a choice — you likely can't "target" sarcoplasmic hypertrophy specifically
The Real Picture
From PMC research (2020-2025):
"If an individual exhibits a 20% increase in mean fiber cross-sectional area, and assuming myofibrils constitute ~85% of intracellular space, a 17% addition of myofibrillar protein and a 3% increase in sarcoplasm volume would accompany fiber growth."
Translation: When muscles grow, both compartments expand. The sarcoplasm grows too—but at a slower rate than the myofibrils.
However, some evidence suggests that training history influences the ratio:
- High-rep training may favor relatively more sarcoplasmic expansion
- Heavy training may favor relatively more myofibrillar growth
- The difference is small (~10-15% of total growth), not a complete transformation
Why Bodybuilders Look Different
The strength difference between bodybuilders and powerlifters isn't because bodybuilders have "non-functional" sarcoplasmic hypertrophy. It's because:
- Neural adaptation — Heavy lifters practice specific movements
- Skill specificity — Strength is pattern-specific
- Muscle architecture — Bodybuilders may develop longer muscle bellies
Practical Takeaways
- Don't chase "sarcoplasmic hypertrophy" specifically — Just train for muscle growth; your body will figure out the optimal ratio
- Both heavy and light training build muscle — The key driver is proximity to failure, not load
- The pump feels real — Sarcoplasmic expansion does occur, just not in the dramatic "non-functional" way claimed
- Periodize both — Use heavy loads for strength, moderate loads for hypertrophy, and occasionally high-rep pump work for variety and metabolic stress
The Verdict
Sarcoplasmic hypertrophy is real—it just isn't the magical "bigger but weaker" phenomenon described in gym mythology. When your muscles grow, both the contractile machinery and the surrounding fluid/protein matrix expand. The ratio may be slightly influenced by training style, but you can't selectively train one type over the other.
Stop worrying about which "type" you're building. Focus on progressive overload, eating in a surplus, training close to failure, and letting your muscles adapt naturally.
References:
- Trappe et al. (2020). Sarcoplasmic Hypertrophy in Skeletal Muscle. PMC
- Sport Sciences for Health (2025). Myofibril vs Sarcoplasmic Training Effects. Springer Nature
- Stronger By Science (2020). Sarcoplasmic Hypertrophy: The Bros Were Probably Right