Final answer:
The exercise that is considered a closed kinetic chain (CKC) exercise is the squat, where the feet are fixed and both the hips, knees, and ankles move. A bicep curl causes the forearm to flex toward the shoulder in an isotonic contraction, while the triceps' contraction would extend the arm, opening the limb.
Step-by-step explanation:
Closed Kinetic Chain Exercises
Closed kinetic chain (CKC) exercises involve movements where the hand or foot is in a fixed position, and movement occurs around the fixed distal segment using multiple joints. Typically, these exercises are weight-bearing where the end of the extremity is stationary, and the force applied by the body is significant. The given options A, B, C, and D comprise different types of exercises, and the one that is considered a CKC exercise is the squat. In the squat, the feet are fixed on the ground, and movement occurs at the hips, knees, and ankles. This contrasts with an exercise like the bicep curl, which is an example of an open kinetic chain (OKC) exercise where the hand moves freely and there is an isolated movement at one joint.
During a bicep curl, the biceps contract and pull the forearm up towards the shoulder, which is a form of flexion. This action is more likely to be an isotonic contraction because the muscle changes length (shortens) and moves a load. Conversely, if the triceps were to contract, they would extend the arm, moving it in the opposite direction of the curl by opening the limb.