Which of the following muscles is primarily involved in supporting the lower back?

The transverse abdominis is primarily involved in supporting the lower back due to its role as a stabilizing muscle for the core. This deep abdominal muscle functions by providing support to the spine, helping to maintain intra-abdominal pressure, and stabilizing the pelvis and lumbar region. When activated, it acts like a natural corset, providing structural support to the lumbar spine and reducing strain on the lower back.

This support is crucial for maintaining proper posture and preventing injuries, particularly during activities that involve lifting or twisting. Strengthening the transverse abdominis can improve overall back health by ensuring that the spine is adequately supported during movement. In contrast, the other muscle groups listed, such as the deltoids, biceps, and hamstrings, have different primary functions and do not play a direct role in the stability of the lower back.