NETA Personal Trainer Exam 2026 – 400 Free Practice Questions to Pass the Exam

The concentric phase is characterized by the shortening of the muscle as it generates enough force to overcome resistance, such as lifting a weight. During this phase, the muscle fibers contract, bringing the origin and insertion of the muscle closer together. This typically occurs during activities like lifting a dumbbell during a bicep curl, where the biceps brachii shortens to lift the weight against gravity.

In contrast, the eccentric phase involves the lengthening of the muscle as it gradually decreases tension while controlling the movement, such as lowering a weight. The isometric phase occurs when the muscle exerts force without changing its length, maintaining a static position. The resting phase refers to intervals between muscle contractions where no tension is being generated. Thus, the concentric phase clearly stands out as the phase in which the muscle actively shortens.