Concentric and eccentric contractions describe what happens to a muscle's length while it produces force. In a concentric contraction, the muscle shortens because the force it generates exceeds the resistance, as in the lifting phase of a biceps curl. In an eccentric contraction, the muscle lengthens while still producing force because the resistance exceeds that force, as in lowering the weight back down under control. A third type, isometric, produces force without a noticeable change in muscle length.
When to use each
- Concentric work is associated with producing movement: standing up, pushing, jumping, and lifting.
- Eccentric work is associated with controlling and decelerating movement: lowering, landing, slowing down, and changing direction.
- Eccentric contractions can produce more force than concentric contractions at a similar speed, and unaccustomed eccentric exercise is commonly linked with delayed-onset muscle soreness.
- Strength programs often adjust the tempo of each phase, for example a slow lowering phase followed by a faster lift.
How to see it on video
Muscles cannot be seen contracting on ordinary video, but the type of contraction can often be inferred from joint motion and the direction of the load. During a squat descent, the knees and hips flex under body weight, so the knee and hip extensors are working eccentrically. During the ascent, the same muscles work concentrically. Timing each phase frame by frame, or with a stopwatch such as the one in KineVision, shows whether lowering is controlled or rushed.
Common mix-ups
- Lowering is not passive. In a controlled descent, the working muscles are active even though they are lengthening.
- The muscle group depends on the direction of gravity, not just on which way the joint moves. In a push-up, the elbow extensors work eccentrically as the elbows flex on the way down.
- The word contraction suggests shortening, so some texts prefer the term muscle action, especially for eccentric work.
Recognizing which phase is concentric and which is eccentric helps when describing technique, setting tempo, and interpreting where a movement loses control.