AFAA Personal Trainer Certification Practice Exam

Which muscle is considered to have no actual joint action?

1. Hamstrings

2. Transverse abdominals

3. Rectus abdominis

4. Deltoids

The correct answer is: Transverse abdominals

The transverse abdominis is often described as having no actual joint action because it primarily functions as a stabilizing muscle rather than a muscle that creates movement at a joint. This deep abdominal muscle plays a crucial role in core stability and contributes to maintaining intra-abdominal pressure. By providing support to the spine and pelvis, it helps to stabilize the body during various movements, particularly those that require the core to be engaged while the limbs are moving. In contrast, the other muscles listed do have joint actions. The hamstrings flex the knee and extend the hip, the rectus abdominis flexes the lumbar spine, and the deltoids abduct the arm. Thus, the classification of the transverse abdominis as a non-joint action muscle highlights its unique role in maintaining stability and supporting dynamic movement rather than directly facilitating specific joint movements.