When you’re curling a dumbbell up toward your shoulder, your bicep muscle is shortening. That’s a concentric contraction. An eccentric contraction occurs when a muscle is actively lengthening. This typically happens when the muscle is approaching the maximum amount of force it can generate. A study published in the journal Medicine and Science in Sports and Exercise analyzes the effect of high-force eccentric exercise on muscle cell growth.

Researchers had 9 recreational athletes perform 300 eccentric leg extension actions to work their knee extensors. Muscle biopsies conducted 24 hours into recovery showed increased satellite cell formation in Type II fast twitch muscle fibers, the type of muscle used for short bursts of strength and speed.

True Strength Moment: Satellite cells play an important role in the growth, repair and regeneration of muscle. If you can work some eccentric contractions into your muscle development efforts, the end result might help you get a little closer to your goals. You probably won’t have to do quite the number of reps used in this study.