Which of the following movements would MOST likely be performed isokinetically?

Isokinetic movement refers to the type of muscular contraction that occurs when a muscle shortens at a constant speed throughout the entire range of motion, often facilitated by specialized equipment such as an isokinetic dynamometer. The device allows for the measurement of peak torque and can provide resistance that matches the efforts of the user, ensuring that velocity remains constant.

In the case of knee extension on an isokinetic dynamometer, the dynamics of the equipment ensure that as the person extends their knee—whether they are applying maximal force or lesser force—the speed at which the knee moves remains constant throughout the exercise. This characteristic distinguishes it as an isokinetic activity.

In contrast, lifting a barbell involves varying speeds and resistances depending on the lift's prevalent forces; holding a plank involves isometric contraction with no change in joint angle at all; and walking upstairs is a dynamic activity that is not performed at a constant speed. Therefore, only knee extension on an isokinetic dynamometer satisfies the definition of isokinetic movement due to the specific controlled environment that allows for constant velocity muscle contractions.