When we think about muscle contractions we usually picture the flexing portion. You know this one, it’s what happens when someone says “flex” so you hold up your arm, contract your bicep, and bend your elbow until you’ve got a nice bulging lump to show off. This is however, not the only kind of contraction your muscle can do. Eccentric contractions are different, and very important.
What An Eccentric Contraction Is
Sit in a chair. Now kick one leg straight out. As your knee straightens, you will notice your thigh musculature flexing. This is a concentric muscle contraction, meaning that as the muscle contracts it is also shortening, which is what pulls your lower leg straight. Now imagine someone is pushing your extended leg down towards the floor, but you are resisting. The pushing person is stronger than you, so you can’t stop them, but you can slow them down. In this case, your thigh muscles are contracting but they are also lengthening at the same time. That is an eccentric contraction—the muscle contracts but also lengthens.
What Eccentric Contractions Do
Your body uses eccentric contractions to help control movement. Sticking with the thigh muscles for a moment (quadriceps), squatting is a great example of a movement where eccentric contractions are pivotal. In the downward phase of a squat, your knee is bending. However, since you don’t want to fall into the squat, you need your quads to work just like they did in the pushing person analogy above. They need to contract while the knee bends in order to slow the bending down and keep you from crashing into the floor. They are, in essence, the brakes that keep you from losing control.
Related: How To Do Squats
How Eccentric Contractions Affect You
The thing about eccentric contractions is that most of us aren’t consciously aware of them. They are not as intuitive to understand as concentric contractions, where we can clearly see a muscle working as it flexes and bulges. But eccentric contractions are happening all the time and they affect us.
First and foremost they are hugely important for normal movement. Eccentric contractions slow down and stop movements, giving you control over speed and intensity. Without them, instead of having nice, smooth, controlled movement you’d be jerking around like Frankenstein.
A notable effect of eccentric contractions is the intense soreness they can create. Lengthening while contracting puts a very large strain on muscles so when your exercise involves a lot of intense eccentric work you can get very, very sore. Spin classes are an example of an exercise that is heavy on eccentric work—it happens as your legs slow and control the spinning wheel during the return phase of pedalling.