A concentric contraction is a muscle action in which the muscle-tendon unit shortens while producing force. It occurs when the torque created by the muscle at a joint is greater than the opposing torque from gravity, a load, or another external force, so the joint moves in the direction the muscle pulls.
Concentric actions do positive mechanical work: they add energy to the body or to an implement. They are typically associated with accelerating, lifting, pushing, and propelling.
Common Examples
- The quadriceps and hip extensors during the upward phase of a squat
- The biceps during the lifting phase of a curl
- The calf muscles during push-off in running or jumping
- The chest and triceps while pressing a bar away from the body
At a given speed, muscles can generally produce less force concentrically than eccentrically, and concentric force capacity decreases as shortening velocity increases. This force-velocity relationship helps explain why very fast movements cannot also be maximally forceful.
Observing It in Video
Muscle actions cannot be seen directly, but they can be inferred from joint motion and the direction of the load. If a joint is extending while lifting a weight upward against gravity, the extensor muscles are most likely working concentrically. Frame-by-frame review and joint-angle measurement can show when a concentric phase begins, how long it lasts, and how joint angles change through it.
Limits and Pitfalls
- The same joint motion can involve different muscles depending on the direction of the load, so the external force must be considered
- Video shows movement, not muscle activation or force; electromyography or force measurement is needed for that
- Momentum from a previous phase can make a concentric phase look easier or faster than the muscles alone would produce
- In multi-joint movements, some muscles may be shortening while others are lengthening at the same time
Identifying concentric phases is useful for describing technique and timing, such as where a lift slows down or how quickly a jump transitions to push-off.