Football, similar to many other intermittent team sports, requires multiple accelerations, decelerations and changes of direction. In this respect participants must be conditioned to withstand the high forces that these intense actions produce, in all planes of motion.
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). According to Behm (2010) the core is defined as ‘the axial skeleton (including the shoulder girdle and hip girdle) and all the soft tissues that attach to it proximally. Some of the major muscles of the core include; multifidus, erector spinae, quadratus lumborum, transverse abdominis, rectus abdominis, external oblique abdominis, internal oblique abdominis, psoas major, pelvic floor muscles and diaphragm. 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.
As previously mentioned, when there is flexion of the spine in addition to compression, the load that the spine can withstand decreases and the risk of injury dramatically increases (Gunning, 2001). Therefore, the safest way to train the core is to ensure that the spine remains in a neutral position when any load is introduced to the body. While flexion movement is defined as bending the spine forward, a flexion moment is a kinematic term used to describe creating a moment or torque. Moments can be created independently regardless of any movement. Pushing an immoveable object requires the spine to stiffen with anterior muscle activation to avoid energy leaks and prevent spinal flexion. Therefore, these muscle create a flexion moment rather than movement. Enhancing stiffness with flexion moment while avoiding flexion movement is essential to eliminate the micro trauma that lead to pain (McGill, 2010).
Abdominal co-activation increases the stiffness of the spine, promoting stability in the vertebral segments (Vera-Garcia, 2007). Research shows that exercises that co-activate TVA, QL and multifidus and minimize rectus abdominis activity are critical for spine stabilization programs. Therefore, these muscles must work harmoniously to achieve this goal. Using an approach that isolates 1 or 2 muscles should not be specific targets when strengthening the spine, instead stabilization exercises should be used to produce a more global co-activation such as that produced during abdominal bracing.
A systematic review found that multi joint free weight exercises such as squat and deadlift, were best for optimizing the recruitment of these muscles compared with isolated exercises exclusively targeting the core (Martuscello, 2013). Free weight multi joint exercises typically involve external loading and when performed in addition to a progressive overload have multiple health benefits including increasing muscle mass, improved mobility and stability, bone density, improved body composition and cardiovascular health. None of these benefits are associated with isolated core or stability exercises alone. As compound movements simultaneously activate multiple major muscle groups and act upon multi joint systems there is more of a functional carry over into sport performance.
Training the whole core musculature in order to strengthen the spine should therefore, consist of ensuring the spine remains in a neutral position and progressing core exercises with moments rather than movements. This will reduce the risk of injury while also increasing dynamic stability of the spine.