Final answer:
Excessive forward lean during an overhead squat assessment is most likely caused by lordosis, an excessive anterior curvature of the lumbar region.
Step-by-step explanation:
Excessive forward lean during an overhead squat assessment can be caused by disorders of the vertebral column, such as kyphosis or lordosis. Kyphosis is an excessive posterior curvature of the thoracic region, while lordosis is an excessive anterior curvature of the lumbar region. Both conditions can be caused by developmental anomalies, pathological changes, or obesity, and can result in abnormal or excessive curvatures of the spine. In the case of excessive forward lean during an overhead squat assessment, it is likely that lordosis is the cause due to the anterior tilt of the pelvis and enhancement of the lumbar curve.