Final answer:
To maintain a healthy back, the quadratus lumborum should be strengthened, as it is part of the posterior abdominal wall that aids in stabilizing the body and posture.
Step-by-step explanation:
To maintain a healthy back, it is vital to strengthen the quadratus lumborum. This muscle is part of the posterior abdominal wall and plays a crucial role in stabilizing the body and aiding in proper posture. The quadratus lumborum is positioned in the lower back on either side of the lumbar spine, and it connects the pelvis to the spine.
When we consider the options provided in the question, the quadratus lumborum is the muscle group that must be strengthened for a healthy back (a) Quadratus lumborum). Strengthening this muscle can be done through exercises like side planks, bird dogs, and lunges, which all target the lower back and core muscles. Strong quadratus lumborum muscles support the spine and contribute to overall core stability, significantly reducing the risk of back pain and injuries.