I was just reading an article about the damages in the muscle during an eccentric muscle contraction compared to concentric contraction. I’ve known for a long time that eccentric contractions cause a lot greater micro damages in the working muscle.
I also knew why that happens – because during the eccentric (negative) phase of the rep the weight is pulling in the opposite direction of the contraction or shortening of the muscle fiber. What I didn’t know is how to explain it more scientifically.
It sounds like this: during the concentric (the positive) phase of the rep the force decreases while the speed increases. In the case of the eccentric contraction (the negative part of the rep) the force increases while the speed increases. In other words the faster you move the weight during the eccentric (negative) part of the rep the more muscle damage you cause – that is more of the contracting filaments get micro damaged.
Later on when the body goes on to repair the damaged parts of the muscle fiber, a positive adaptation occurs – the body re-builds the damaged parts of the muscle cell, making them stronger by increasing the number of contracting filaments. That’s how we grow.