Muscles drive all human movement, powered by contractions that generate force within the body. Concentric exercises involve one of the three primary ways a muscle activates, overcoming resistance to produce visible motion. Understanding this action is key to grasping how we build strength and perform physical tasks.
Defining Concentric Muscle Action
A concentric contraction occurs when a muscle shortens while generating enough force to overcome an external resistance, such as gravity or a barbell. This is often called the “lifting” or “positive” phase of an exercise. During this phase, the muscle actively shortens to move a load. For example, the upward phase of a bicep curl, where the forearm moves toward the shoulder, is a concentric action of the biceps muscle.
The underlying mechanism involves the sliding filament theory within the muscle fibers. Inside the muscle’s sarcomeres—the basic contractile units—the thick (myosin) and thin (actin) protein filaments slide past one another. This interaction pulls the Z-lines closer together, causing the muscle structure to shorten and generate tension. The standing-up portion of a squat or pushing away from the floor during a push-up illustrate this shortening action.
Concentric vs. Eccentric and Isometric Actions
Concentric action is one of three distinct ways muscle tissue generates tension, alongside eccentric and isometric actions. The difference lies in what happens to the muscle’s length during the contraction. Concentric action involves muscle shortening, while eccentric and isometric actions involve lengthening or no change in length, respectively.
An eccentric contraction occurs when the muscle lengthens under tension, acting as a brake or decelerator against an opposing force. In a bicep curl, this is the controlled lowering of the weight back down to the starting position. Muscles are able to handle significantly more load during the eccentric phase than they can concentrically lift.
Conversely, an isometric action occurs when the muscle generates force but its length remains unchanged, resulting in a static hold. If you paused a bicep curl halfway through and held the weight motionless, that would be an isometric contraction. While these three actions are mechanically distinct, they rarely occur in isolation, instead happening sequentially in most exercises and functional activities.
The Role of Concentric Movement in Strength Training
In strength training, the concentric phase is the direct expression of force output and the primary mechanism for overcoming inertia. This action is responsible for the ability to accelerate a mass and is tied to the development of explosive power. Concentric training is effective for improving the rate of force production, which measures how quickly a muscle can generate maximal force.
The ability to successfully lift a heavy weight is determined by the strength generated during the concentric phase, since muscle tension must exceed the load to initiate movement. Training this phase enhances functional performance, as many daily activities, such as standing up from a chair or climbing stairs, rely on concentric muscle shortening. Furthermore, because concentric movements produce less mechanical and cellular muscle damage compared to eccentric movements, they result in less post-exercise soreness and allow for faster recovery, supporting higher training frequency.