National Academy of Sports Medicine (NASM) Group Fitness Instructor Practice Exam

What is the isolated function of the quadriceps muscle group?

1. Concentrically accelerates hip flexion

2. Concentrically accelerates knee flexion

3. Concentrically accelerates knee extension

4. Concentrically accelerates ankle plantar flexion

The correct answer is: Concentrically accelerates knee extension

The quadriceps muscle group is primarily responsible for extending the knee joint. This action is crucial during various movements such as standing up, walking, running, and jumping. The quadriceps, which consist of four muscles (rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius), work together to concentrically contract and produce knee extension. When considering the isolated function of the quadriceps, it is important to recognize that while they play a role in other movements, their main isolated action is indeed knee extension. Therefore, stating that they "concentrically accelerate knee extension" accurately reflects their primary function in human biomechanics. Understanding this function is critical for trainers and instructors looking to design effective workout programs targeting strength and flexibility in the legs. The other options involve muscle groups that are not the primary function of the quadriceps, such as hip flexion or ankle plantar flexion, which are primarily engaged by different muscle groups. This distinction highlights the specificity of muscle functions in athletic and fitness activities.