Prone hip extensions are very commonly used in rehabilitation for musculoskeletal disorders, particularly for assessing lumbopelvic stability. (strengthandconditioningresearch.com)
They lack lumbopelvic rhythm and there is excessive flexion or extension somewhere in the spine as a compensation. (onnit.com)
There are plenty of people out there who have a «six - pack» but they can not functionally brace their spine or lumbopelvic region. (weckmethod.com)