There are many definitions of core stability. Core Stabilisation (CS) has been described as the ability to maintain spinal and pelvic alignment using trunk and hip muscle endurance and strength (Yu & Lee, 2012: Wilson et al, 2005). It has also been described as an action whereby muscles stabilise the spine statically or dynamically while other muscles carry out a movement involving other joints (Siff, 2004).

In simple terms, core stability is the process of holding the shoulder and pelvic girdles (that is, the centre part, or core of the body) stable in order to support the movement forces from the arms and legs, which in turn will also increase the ability to balance.

To do this, the muscles that are responsible for the stabilising role must function correctly in order that the muscles responsible for movement are able to perform their function correctly.

CS first appeared in the literature in studies that investigated the link between motor control of the trunk muscles and back pain (Richardson & Hodges 1997, 1998).

There is general consensus that an improvement in CS can help to reduce the incidence of back pain. What is less clear is the relationship to athletic performance.

It has been stated however that CS plays an essential role in the process of conveying energy from the trunk to the extremities (Abt, et al., 2007; Scibek, 1999; Tse, et al., 2005). It has also been found that weak CS combined with strong lower body musculature could lead to fatigue and insufficient force generation that may be damaging to aspects of exercise or sport performance (Nesser, et al., 2008; Tse, et al., 2005).

Core stability training is now commonplace in both health and fitness and sports injury environments. Many exercise programmes such as Pilates, yoga, and Tai Chi have become popular around the world and most follow core strengthening principles.

For many years people have relied on the ‘sit-up’ as the main exercise for the core yet it has been demonstrated that the psoas (hip flexors active in sit-ups) is only a feeble flexor of the lumbar spine and exerts massive compressive forces on the lumbar disks during such activities (Bogduk 1997, Siff 2004).

Muscles associated with core stability

The everyday demands placed on the posture and control of the human body mean that the muscles responsible for core stabilisation (stabilisers; also known as tonic muscles) are designed to perform endurance tasks rather than short-term or explosive tasks. These muscles are sometimes described as ‘nature’s corset’ and are required to carry out a stabilising role for long periods of time.

Due to the demands of these endurance-type tasks, stabilisers are predominantly made up of type I slow-twitch fibres. In normal function, while the role of stabilisation is being undertaken, muscles known as mobilisers are able to carry out their role of locomotion or movement of the body. These muscles are usually required to provide a short-term or phasic role, and are therefore not classed as endurance muscles. Mobiliser muscles are often found to be predominantly made up of fast-twitch fibres and are more superficial (closer to the surface) than stabiliser muscles.

Inner and outer units

There is a body of research that suggests both deep and superficial muscles in the trunk and pelvic region contribute in some way to spinal stabilisation (Richardson et al., 2003).

Essentially. the research purports that muscles in the body that are deep can be referred to as local muscles or, in relation to core stabilisation, as the inner unit. The transversus abdominis, multifidus, pelvic floor, diaphragm and internal obliques are all examples of local muscles.

Muscles that are superficial are commonly known as global muscles or the outer unit. The rectus abdominis, external obliques and some parts of the erector spinae are all global muscles.

At the hip joint, the gluteus maximus and gluteus minimus are usually considered to be mobilisers and the gluteus medius is normally considered to be a stabiliser. There are many more muscles associated with stabilisation of the hip complex, but the main ones are mentioned above.

It was demonstrated by Hides et al in 1996 that local muscles such as multifidi have been found to atrophy in people with chronic low back pain (LBP) and also that patients with LBP have delayed contraction of the transversus abdominis and multifidi prior to limb movement (Hodges et al 1996).

Research related to performance and injury

CS training methods are now commonly used to enhance performance, however, according to Willardson, 2007 stability ball training is limited in its ability to do this.

Schibek, et al in 2001 found that stability ball training improved core stability in swimmers, but did not improve swim times. Similarly, in 2004 Stanton et al concluded that stability ball training improved core stability but did not enhance running performance or running posture.

In 2008 Koshida et al stated that the value of unstable training for limb muscles is uncertain and limited high levels of intensity cannot be achieved under unstable conditions. Around the same time, Nuzzo et al also suggested that a limitation when strength training under unstable conditions is decreased force-generation, as limb muscles assist in joint stability, which supports the work carried out by Anderson et al in 2004.

For this reason it has been suggested that instability training devices should only be used to supplement traditional training methods (Wahl & Behm, 2008) whereas others have suggested that unstable training is of little value because of the lack of evidence to support performance gains (Stanton et al., 2004). Some even purport that for enhanced performance, free-weight training on a stable surface might be more beneficial as exercising in a supine or prone position on the stability ball may not transfer to sports performed primarily in standing positions (Willardson, 2007).

There is however research that supports the use of CS training in relation to performance. A recent Systematic review of CS training programmes concluded that CS training can elicit marginal improvements to athletic performance but suggests that further research is needed to determine if there is an optimal CS training method (Reed et al, 2012).

Conclusion

Even though core strengthening has a strong theoretical base relating to prevention (and treatment) of injury such as lower back pain, studies are limited and often conflicting. Stability ball training does result in benefits, such as improved core strength for injury prevention and enhanced heart-rate response and oxygen consumption. It may be prudent however to incorporate as a supplement to other types of training, especially in consideration of the benefits of free-weight training and, as stated by Kibbler in 2006, ‘the core is particularly important in sports because it provides proximal stability for distal mobility’.

TESTING

There is a lack of consensus relating to valid measurement of core stability, although there are several tests that purport to indirectly measure stability.

TA contraction test

There are various reasons why testing core stabilisation (indirectly) would be useful. One reason would be to verify if any training techniques were positively affecting stabilisation. The other would be to make sure that the individual was able to contract TA sufficiently enough to progress to more advanced exercise techniques.

If an individual was not able to maintain TA contraction throughout an exercise performance, then they should be given an easier alternative. One of the indirect methods of testing core stabilisation is that proposed by Richardson et al, which uses a bio-feedback pressure unit to measure the degree of contraction of the TA. This method has been validated against the direct method of inserting fine wire electrodes into the intervertebral discs to measure pressure changes. The protocol for testing TA contraction is as follows:

  1. Have the individual lie in a prone position and place the bio-feedback pressure cuff under the transversus abdominis muscle (the navel should be in the centre of the cuff) as in figure 1.
  2. Inflate the cuff to 70mmHg.
  3. Ask the individual to draw in the abdomen whilst maintaining normal breathing.
  4. Any movement of the pelvis is to be avoided.
  5. Record the pressure decrease on the bio-feedback unit.

The TA Testing position

As there are no normative values for this particular test, any decrease in pressure indicates a degree of TA contraction. The test results can then be used as a baseline to monitor progression. Repeat testing would normally be done every 10-12 weeks to allow adaptation to any exercise programme that was undertaken.

by Morc Coulson
Senior Lecturer in Sport and Exercise Sciences at the University of Sunderland

For further reading on core stability and for a comprehensive guide to Personal Training, read Morc’s REPs-endorsed book “The Complete Guide to Personal Training 2nd edition”, available from all major book retailers and Amazon.

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REFERENCES

Akuthota, V., & S.F. Nadler. (2004) Core strengthening. Archives of Physical Medicine and Rehabilitation, 85:86-92

Anderson, K.G. & Behm, D.G. (2004) Maintenance of EMG activity and loss of force output with instability. Journal of Strength and Conditioning Research, 18(3):637-640

Bogduk, N. (1997) Clinical Anatomy of the Lumbar Spine and Sacrum, 3rd ed.
New York: Churchill Livingstone

Cairns, M.C., Foster, N.E. & Wright, C. (2006) Randomized controlled trial of specific spinal stabilization exercises and conventional physiotherapy for recurrent low back pain. Spine, 31:E670-E681

Cholewicki, J., Juluru, K., & McGill, S.M. (1999) Intra-abdominal pressure mechanism for stabilizing the lumbar spine. Journal of Biomechanics, 32:13-17

Fredericson, M., & Moore, T. (2005) Muscular balance, core stability, and injury prevention for middle- and long-distance runners. Physical Medicine and
Rehabilitation Clinics of North America, 16:669-689

Grenier, S.G., & McGill, S.M. (2007) Quantification of lumbar stability by using two different abdominal activation strategies. Archives of Physical Medicine and Rehabilitation 88:54-62

Hicks, G., Fritz, J.M., & Delinto, A. (2005) Preliminary development of a clinical prediction rule for determining which patients with low back pain will respond to a stabilization exercise program. Archives of Physical Medicine and Rehabilitation 86:1753-1762

Hides, J.A., Richardson, C.A., & Jull, G.A. (1996) Multifidus muscle recovery is not automatic after resolution of acute, first-episode low back pain. Spine, 21:2763-2769

Hodges, P.W., & Richardson, C.A. (1996) Inefficient muscular stabilization of the lumbar spine associated with low back pain. A motor control evaluation of transversus abdominis. Spine, 21:2640-2650

Hodges, P.W. (2003) Core stability exercise in chronic low back pain. Orthopedic Clinics of North America, 34:245-254

Jakubek, M.D. (2007) Stability balls: Reviewing the literature regarding their use and effectiveness. Strength and Conditioning Journal, 29 (5):58-63

Kibler, W.B., J. Press, & Sciascia, A. (2006) The role of core stability in athletic function. Sports Medicine, 36:189-198

Klenerman, L., Slade, P.D., & Stanley, I.M. (1995) The prediction of chronicity in patients with an acute attack of low back pain in a general practice setting. Spine, 20:478-484

Koshida, S., Urabe, Y., Miyashita, K., Iwai, K. & Kagimori, A. (2008) Muscular outputs during dynamic bench press under stable versus unstable conditions. Journal of Strength and Conditioning Research, 22 (5):1584-1588

Nuzzo, J.L., McCaulley, G.O., Cormie, P., Cavill, M.J. & McBride, J.M. (2008) Trunk muscle activity during stability ball and free weight exercises. Journal of Strength and Conditioning Research, 22 (1):95-102

McGill, S. (2002) Low Back Disorders: Evidence-based prevention and rehabilitation.
Champaign, IL: Human Kinetics

Richardson, C., Jull, G., Hodges, P., & Hides, J. (2003) Therapeutic Exercise for Spinal Segmental Stabilization in Low Back Pain, Churchill Livingstone

Schibek, J.S., Guskiewicz, K.M., Prentice, W.E., Mays, S. & Davis, J.M. (2001) The effect of core stabilization training on functional performance in swimming. Master’s thesis, University of North Carolina, Chapel Hill

Stanton, R., Reaburn, P.R. & Humphries, B. (2004) The effect of short-term Swiss ball training on core stability and running economy. Journal of Strength and Conditioning Research, 18 (3):522-528

Wahl, J.M. & Behm, D.G. (2008) Not all instability training devices enhance muscle activation in highly resistance-trained individuals. Journal of Strength and Conditioning Research, 22 (4):1360-1370

Willardson, J. (2007) Core stability training: Applications to sports conditioning programs. Journal of Strength and Conditioning Research, 21 (3):979-985

Wilson, J.D., Dougherty, C.P., Ireland, M.L., & Davis, I.M. (2005) Core stability and its relationship to lower extremity function and injury, Journal of American Orthopaedic Surgery: 13; 316-325
Yu, J.H., & Lee, G.C. (2012) Effect of core stability training using pilates on lower extremity muscle strength and postural stability in healthy subjects, Journal of Isokinetic and Exercise Science: 20; 141-146

Suggested further reading

Behm, D.G., Leonard, A.M., Young, W.B., Bonney, A.C. & MacKinnon, S.N. (2005) Trunk muscle electromyographic activity with unstable and unilateral exercises. Journal of Strength and Conditioning Research 19(1): 193-201.

Cosio-Lima, L.M., Reynolds, K.L., Winter, C., Paolone, V. & Jones, M.T. (2003) Effects of physical ball and conventional floor exercises. Journal of Strength and Conditioning Research, 17: 475-483

Hamlyn, N., Behm, D.G. & Young, W.B. (2007) Trunk muscle activation during dynamic weight training exercises and isometric instability activities. Journal of Strength and Conditioning Research 21(4): 1108-1112

McGill, S. (2007) Low back disorders. Evidence-based prevention and rehabilitation (2nd edition). Champaign, Illinois: Human Kinetics

Norris, C.M. (2000) Back stability. Champaign, Illinois: Human Kinetics

O’Sullivan, Twomey, Allison (1997) Evaluation of specific stabilising exercise in the treatment of chronic low back pain with radiologic diagnosis of spondylosis or spondylolisthosis. Spine, 22(24): 2959-2967

Robinson, R. The new back school prescription: Stabilization training part 1. Occupational medicine, 7: 17-31. 

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