Which of the following exercises is classified as a single-joint exercise?

The triceps extension is classified as a single-joint exercise because it primarily involves movement at only one joint, which in this case is the elbow. This exercise specifically targets the triceps muscle at the back of the upper arm, allowing for isolation of that muscle during the movement. By focusing on one joint, the triceps extension emphasizes strength building in the triceps without significantly engaging other muscle groups or joints.

In contrast, squat, deadlift, and bench press exercises involve multiple joints and muscle groups. The squat engages the hips, knees, and ankles, focusing on the lower body muscles. The deadlift primarily targets the posterior chain, involving the hips and knees as well as the back. The bench press works on the shoulders and elbows together with the chest muscles, making them all compound exercises rather than single-joint movements.