Concentric phase
Also known as: Positive phase
The concentric phase is the part of a movement in which an active muscle produces force while shortening overall. It is often called the lifting or positive phase. Rising from a squat, lifting a dumbbell in a curl, and pulling a lat-pulldown handle toward the torso are common examples.
"Up" and "down" do not reliably identify the concentric phase. The lat-pulldown handle travels downward while the latissimus dorsi shortens, whereas lowering a dumbbell downward is eccentric for the elbow flexors. Identify the muscle being discussed, its joint action, and whether it is shortening under force. Different muscles can also perform different roles during the same movement.
In most dynamic repetitions, the concentric phase follows an eccentric phase, sometimes with an isometric pause between them. Changing the rep tempo alters the task: pausing can remove rebound, and moving slowly on purpose can reduce the load or repetitions completed. Neither a pause nor a deliberately slow lift is required for every goal.
Concentric intent and actual velocity are distinct. For muscular power, the athlete usually intends to accelerate as rapidly as the exercise permits. A heavy bar can still move slowly despite maximal intent, while a light load can move fast against a lower external force demand. Load, fatigue, technique, and the exercise’s resistance profile shape the observed speed.
A repetition often slows at a sticking region where leverage and available muscle force are least favorable. That slowdown is not automatically technical failure if the chosen form remains intact. End the set according to its purpose: a power set may stop at meaningful velocity loss, while a hypertrophy or strength set may include slower but controlled concentric phases.