Final answer:
To address muscle imbalances and sway-back posture, strengthening the abdominal muscles is recommended. This approach helps to support and align the trunk, minimizing strain on the back muscles and improving posture. The erector spinae also contribute to postural support and must be well-conditioned.
Step-by-step explanation:
When dealing with muscle imbalances and sway-back posture, the recommended approach is strengthening the abdominal muscles. This is because the muscles of the abdominals, which include the external obliques, the internal obliques, the transversus abdominis, and the rectus abdominis, work in concert to support and stabilize the trunk of the body. A good posture involves the upper body's center of gravity (cg) positioned over the hips with no need for excess muscle action to balance the body, as shown in Figure 9.26(a). However, with sway-back posture, as shown in Figure 9.26(b) and 9.29, there is an increased load on the lower back muscles due to a forward displacement of the upper body's cg, creating a torque that these muscles must counteract, often leading to back strain and muscle fatigue. By strengthening the abdominal muscles, an individual can better support and align their trunk, minimize the strain on the back muscles, and improve overall posture.
The deep muscles of the core of the body, including the erector spinae, also play a role in maintaining posture and balancing the body on two feet. The erector spinae, in particular, are responsible for postural support as they stabilize the vertebral column, indicated by the multiple-choice question covered in the reference materials. To maintain a balanced and healthy posture, it is vital that these core muscles are functioning properly and are neither too weak nor overly tight.