Final answer:
To counteract excessive postural thoracic kyphosis, strengthening the trunk extensors, particularly the erector spinae group, is recommended as this muscle group is responsible for extending the vertebral column and maintaining proper posture.
Step-by-step explanation:
Excessive postural thoracic kyphosis is a condition where there is an increased outward curvature of the thoracic vertebrae, often leading to a hunched back appearance. Strengthening exercises for this condition should focus on the muscles that oppose this posture by extending the spine. In particular, the erector spinae group is responsible for maintaining the lumbar curve and extending the vertebral column, making it one of the primary muscle groups to target for strengthening in individuals with thoracic kyphosis.
The erector spinae group is comprised of three major subgroups: the iliocostalis, longissimus, and spinalis, all of which work together to control flexion, lateral flexion, rotation, and most importantly in this case, extension of the vertebral column. Therefore, trunk extensors are the muscle group most likely to require strengthening to counteract the forward curvature associated with thoracic kyphosis.