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So, what is the core and why does it have to be stable?

5 Apr 2017
The concept that a strong and stable ‘core’ is needed to prevent injuries and improve performance in sports continues to be popular in the sports medicine and fitness industries. However, defining the concept of core stability can be difficult without first describing the anatomical structures that contribute to stabilising the body, and the functional needs of athletes. I often ask athletes if they can tell me where their core is. Most point to their abdominal muscles, but are unable to clarify beyond that. When I ask them what they would specifically like to improve about their core, beyond strengthening it, their answers become even more vague.

Stability is an intuitive concept. Athletes want to be stable when they run, kick, or land from a jump. Through training, athletes learn to produce powerful and accurate movements using the muscles of their trunk and limbs. Elite athletes maximise the power, strength and speed of their movements without compromising the fluidity of their performance. To the observer, an elite athlete looks almost relaxed as they outperform their peers. The word ‘stability’ is rarely used, unless the athlete enters a rehabilitation facility or gym.

The spine and the pelvis are inherently stable structures. The spine is S shaped and flexes with the hips, knees and ankles to dissipate forces. The tailbone or sacrum is wedged shaped and sits snugly in the pelvis like a keystone in an old Roman bridge. However, the spine and pelvis are dynamic structures that transfer forces in many directions. To do this, they rely on muscles.

The muscles that support the spine can be described as a global unit and an inner unit. The outermost global unit of muscles are responsible for movement. The inner or core unit are a group of muscles that lie deeper and are capable of less movement and stiffening or stabilisation of the spine. These muscles include:

  • The transversus abdominis (TA), the deepest layer of the abdominal muscles. The TA is the only abdominal muscle with a direct relationship with the spine through its connection via the thoracolumbar fascia. Much like a weight lifters belt or a lady’s corset, when the TA contracts it slides and helps stabilise the trunk. During chronic low back pain, TA function has been shown to be impaired (1, 2). In Australian Rules footballers presenting with groin pain, the TA muscle has shown to be delayed in its function which may explain the often chronic nature of groin pain in athletes (3) 
  • The small deep muscles within the back, particularly Multifidus is a set of muscles that spans from one spinal vertebra to another. Due to its small cross-sectional area and short span Multifidus is not able to produce significant movement of the spine. Instead, Multifidus stiffens the spine so that the larger global muscles have a more stable base from which to produce movement.
  • The diaphragm is one of the most important core muscles. Breath control is an important part of many exercises and is commonly taught during the initial stages of skill acquisition in sport. Try holding your breath and performing a plank. You quickly realise why controlled breathing is important during exercise and the role that the diaphragm plays in stabilising the spine. Poor breathing control can lead to an increase in compressive and shear forces around the spine and pelvis, which can lead to injury. Having a strong inner unit or core muscles can stabilise your trunk and provide a foundation for strong and co-ordinated movement.
  • Finally, back, groin or pelvic pain can also arise from dysfunction of the pelvic floor muscles. The pelvic floor muscles form a supportive sling between the tail bone, or coccyx, and the pubic bone at the front of the pelvis. These group of muscles are responsible for maintaining continence and supporting the joints of the pelvic girdle. A well-design ‘core’ training program will involve monitoring of the function of these muscles.

Image: Pelvic Floor Muscles

With so many potential problems associated with dysfunction of the core muscles, and the performance gains that can be made by improving core muscle function, it is easy to understand why sporting clubs often incorporate core exercises into strength and conditioning programs. Pilates exercises is an example of an approach that directly targets the core and can improve the core muscle activation and strength (4). So what exactly is Pilates? In my next Premax Blog, I will discuss how ‘Pilates takes to the field’ – stay tuned!

References

  1. Hodges PW. Is there a role for transversus abdominis in lumbo-pelvic stability? Manual Therapy. 1999;4(2):74-86.
  2. Ferreira PH, Ferreira ML, Hodges PW. Changes in recruitment of the abdominal muscles in people with low back pain: Ultrasound measurement of muscle activity. Spine. 2004;29(22):2560-6.
  3. Cowan SM, Schache AG, Brukner P, Bennell KL, Hodges PW, Coburn P, et al. Delayed onset of transversus abdominus in long-standing groin pain. Medicine and science in sports and exercise. 2004;36:2040-5.
  4. Endleman I, Critchley DJ. Transversus Abdominis and Obliquus Internus Activity During Pilates Exercises: Measurement With Ultrasound Scanning. Archives of Physical Medicine and Rehabilitation. 2008;89(11):2205-12.



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