An example of flexion is the:

Flexion is a specific type of joint movement characterized by a decrease in the angle between body parts. In the context of a bicep curl, the action involves bringing the forearm towards the shoulder, effectively decreasing the angle at the elbow joint.

The concentric action of a bicep curl occurs when the bicep muscle shortens as it contracts to lift the weight, pulling the forearm upward. This contraction and the resulting movement are clear examples of flexion because the elbow angle is reduced during the lifting phase. Understanding this concept is crucial since it highlights how different types of muscle contractions can facilitate various movements and joint actions.

Other options do not demonstrate flexion. The eccentric action of a bicep curl would involve lengthening the muscle as it controls the weight's descent, which does not result in flexion. Lateral and medial movements associated with jumping jacks do not pertain to the elbow and do not involve flexion at that joint. Instead, they reflect lateral movements of the limbs rather than an angular decrease at a joint.