Maximal Eccentric Exercise Sparks Muscle Growth
by: Robbie Durand
Back in the early 90’s there was a book called Bigger Muscles in 42 Days by Dr. Elliot Darden. The book took a revolutionary approach to training by advocating that people needed to spend less time in the gym but more importantly to emphasize eccentric contractions. Lowering the weight under control brings gravity into play in another fashion. The lowering portion of an exercise is called negative work or eccentric muscle action. During positive work, your muscle fibers are shortening. During negative work the same fibers are lengthening. In the simplest terms, observing the weight stack move during an exercise reveals: up is positive, down is negative. Researchers have long been aware that maximal eccentric contractions result in more muscle damage and more muscle fiber growth, but researchers wanted to compare the differences between maximal concentric contractions and maximal eccentric contractions and how they affected satellite cells.
Satellite cells are absolutely essential for muscle growth and repair, without the activation of satellite cells, muscle won’t grow. Optimal repair and adaptation of skeletal muscle is facilitated by resident stem cells (satellite cells). To understand how different exercise modes influence satellite cell dynamics, researchers measured satellite cell activity in conjunction with markers of muscle damage and inflammation in human skeletal muscle following a single work- and intensity-matched bout of eccentric or concentric contractions. Participants completed a single bout of eccentric or concentric of the knee extensors. A muscle biopsy was obtained before and 24 h after exercise. At the end of the study, peak torque decreased following eccentric exercise but not concentric exercise. The researchers observed no significant changes in muscle soreness in the concentric group but they did observe significant increases in the eccentric group both immediately post-exercise and at 24-hours post- exercise. The researchers found that levels of the inflammatory cytokines interferon gamma-induced protein 10 (IP-10) and monocyte chemotactic protein 1 (MCP-1) were significantly increased in the eccentric condition but not in the concentric condition. The researchers found that in the eccentric group, satellite cell content per muscle fiber increased significantly (by 27%) but there was no significant increase in the concentric group. They observed no differences in satellite cell content changes between muscle fiber types. In conclusion, eccentric but not concentric results in functional and histological evidence of muscle damage that is accompanied by increased satellite cell activity 24 h post-exercise. The research study should be a real wake up call for those athletes that want to grow, to emphasize eccentric contractions during their weight training by lowering the weight slowly with the heaviest weight possible.