Elbow flexion during the concentric phase of a biceps curl is an example of a?

During the concentric phase of a biceps curl, elbow flexion is primarily identified as a joint action. The reason this is the correct choice is that joint actions refer specifically to the movements that occur at a joint as muscles contract. In the case of elbow flexion, the biceps brachii contracts to bring the forearm closer to the upper arm, effectively bending the elbow. This contraction is a fundamental movement that defines the exercise.

While the term "movement pattern" could loosely encompass the overall action of the biceps curl, it does not specifically focus on the mechanics of the joints involved. "Training variable" refers to aspects of a workout that can be manipulated to achieve different training outcomes, which do not directly describe the physiological action occurring during the curl. "Critical event" is often related to key moments in movement that may have a significant influence on performance but does not pinpoint the specific action of elbow flexion itself. Therefore, identifying elbow flexion as a joint action most accurately describes what is occurring in this phase of the exercise.