Which of the following muscles is most involved in stabilizing the trunk?

The rectus abdominus is a key muscle involved in stabilizing the trunk due to its central position in the abdominal region. This muscle runs vertically along the front of the abdomen and plays a crucial role in flexing the lumbar spine, which is essential for maintaining proper posture and stability during various movements. Additionally, the rectus abdominus contributes to core strength and stability, allowing for better control of the pelvis and lower back.

While other muscles like the erector spinae do play a role in stabilizing the trunk, they primarily focus on extending and supporting the spine rather than providing the same level of anterior support as the rectus abdominus. The gastrocnemius and biceps brachii, on the other hand, are more focused on movements in the lower leg and arms, respectively, and are not primarily involved in trunk stabilization.