29/12/2021
The spine moves in 4 directions: flexion, extension, lateral flexion and rotation. Dynamic abdominal exercises such as sit-ups places the lumbar spine into flexion. During spine and hip flexion, compressive forces of over 3000N have been observed in the lumbar spine, suggesting that these exercises should be avoided (McGill, 1995). Repeated lumbar flexion and extension have been shown to cause a stretching of the passive tissues which can lead to small micro tears that can build up over time to cause injury (Callaghan, 2001). An intervertebral disc injury most commonly occurs posteriorly due to a spinal flexion movement with the cause of this due to increased pressure on the posterior side of the disc as the spine goes into flexion.
Increases in core strength may assist in injury prevention, improved coordination, and help provide proper spine function and protection (Handzel, 2003). McGill (2010) suggests that most often during human movement the function of the core is to co-contract, stiffen and prevent motion, rather than produce it, indicating that sit-ups are far from ideal in achieving this.
The power generated by limb muscles must be transferred through a stiffened core in order for the whole body to move efficiently (Lynn, 2016). It is believed that if proper core stability is not maintained when power is developed from the hip and shoulder joints, the spine will bend and loose its natural alignment (Lynn, 2016). This movement of the spine is considered an ‘energy leak’ as power developed from the limbs is absorbed proximally in the soft tissues of the spine and not transferred distally with maximum efficiency (McGill, 2010). Therefore, to make core training possible for any population, the core muscles should be trained as stabilizers rather than prime movers.