Descending part of right trapezius

Upper fibers of left trapezius elevate and retract scapula for shrugs and pulls. Key for posture and overhead strength. Left-side focus corrects imbalances.

The descending part of the left trapezius fibers run downward from neck to scapula on the left side, aiding scapular depression and upward rotation. Key for pull-ups and lat work, preventing shoulder hike.

Iliocostalis thoracis, mid erector spinae, runs parallel to spine from low-mid back to upper ribs, aiding thoracic extension and breathing. Supports rows, pulls, and posture in upper body training.

Tiny interspinalis thoracis muscles between thoracic spinous processes fine-tune extension.

The longest erector spinae muscle, running parallel to the spine from sacrum to mid-back, it extends the spine and maintains upright posture. Essential for deadlifts, squats, and spinal stability in powerlifting. Weakness leads to back rounding under load.

The rhomboid major is a diamond-shaped muscle between your shoulder blades, retracting the scapula for better posture. It stabilizes during rows, pull-ups, and presses, countering slouched shoulders in gym-goers. Weak rhomboids lead to rounded posture and shoulder issues.

The rhomboid minor, above the major, connects upper thoracic spine to the shoulder blade's inner border. It retracts and stabilizes the scapula during upper body pulls. Essential for posture correction in lifters with desk jobs.

Semispinalis thoracis is a deep erector spinae muscle from thoracic spine, extending the vertebral column. Maintains thoracic posture during deadlifts and rows. Prevents slouching in prolonged sitting.