High-load dumbbell overhead press training to muscular failure acutely increases thoracic kyphosis angle, scapular dyskinesis, and forward head posture while reducing core endurance in recreational collegiate weightlifters aged 18–24, whereas training stopped 3–4 repetitions before failure does not produce these changes.

When muscles are pushed to complete exhaustion during heavy lifting, they become too tired to send accurate signals to the brain about body position. The brain responds by losing precise control over the muscles that hold the spine and shoulders in place, causing the upper back to curve more, the head to jut forward, the shoulder blades to move abnormally, and the core to lose its ability to stay stiff. This happens because the tired muscles can no longer generate enough force or respond quickly enough to keep the body aligned.