In SIB 3, I put forward the idea that strengthening the back extensor muscles is a useful preventative approach for lower back pain. The article suggested some practical ways to strengthen the lower back, mainly involving dynamic extension exercises. However, the current vogue in physiotherapy and fitness training
is to focus on what is known as 'core stability' training, which specifically targets the smaller and deeper lumbar spine and trunk muscles. The aim of core stability training is to effectively recruit the trunk musculature and then learn to control the position of the lumbar spine during dynamic movements. This article will attempt to review the theory and research that underlies core stability training and suggest a simple exercise progression to enhance this function.
Hodges and Richardson (1996) discuss how the lumbar spine area is 'inherently unstable'. In practical terms, this means the lumbar spine relies upon sufficient stability from the muscles that actively support the area. This 'active' support comes from four mechanisms; tension from theracolumbar fascia, the intra-abdominal pressure mechanism, the role of the paraspinal muscles and the role of deep lumbar extensors (Lewis et al, 2000).
The theracolumbar fascia (TLF) can provide a tensile support to the lumbar spine via deep-trunk muscle activity. The Transversus Abdominis (TA) and the Internal Oblique (IO) muscles both attach to the TLF. This fascia 'wraps' around the spine connecting the deep trunk muscles to the spine. When the TA contracts it increases the tension in TLF which, in turn, transmits a compressive force to the lumbar spine which enhances its stability. In addition the increased tension of the TLF compresses the Erector Spinae (ES) and Multifidus (MF) muscles, encouraging these to contract and resist spine flexion forces (Lewis et al, 2000).
A pressurised balloon
The intra-abdominal pressure mechanism (IAP) can provide a supportive effect to the whole lumbar area. A co-contraction of the pelvic floor, TA, IO and lower back muscles increases the IAP. In turn, this exerts a tensile force on the rectus sheath. This sheath encloses the Rectus Abdominus (RA) muscle and attaches to the IO and TA, surrounding the abdomen. The tension of the rectus sheath increases the pressure within the abdomen, like a pressurised balloon. This supportive 'bag of air' reduces the compression and shear forces acting on the spine. Research shows that IAP increases before and during lifting heavy objects or weightlifting exercises (Zatsiorski, 1994) and also increases during running (Lewis et al, 2000) endorsing the idea that it plays a crucial role in lumbar stability.
Research also shows the significance of the paraspinal muscles and deep lumbar muscles as important stabilisers. It is likely that these paraspinal and deep lumbar muscles act with a static contraction, to resist any lumbar extension and rotational forces. The paraspinal muscles - Interspinalas and Intertransversarii - provide an individual stabilising effect on their adjacent vertebrae, acting in a similar way to ligaments (Palastanga et al 1994). The deep lumbar muscle - multifidus (MF) - has been shown to be active throughout a full range of motion of the lumbar spine and during movements of the lower and upper limbs (Richardson et al 1990).
From this brief explanation of the anatomy and research into the muscles of the lumbar trunk area, it is clear that the deep-trunk muscles - TA, MF, IO, paraspinal, pelvic floor - are key to the active support of the lumbar spine. The co-contraction of these muscles produce forces via the TFL and IAP mechanism which stabilise the lumbar spine, and the paraspinal and MF muscles act directly to resist the forces acting on the lumbar spine.
Early recruitment of the TA and MF muscles
Further study showed that it is not just the recruitment of these deep-trunk muscles, but how they are recruited that is important. Hodges and Richardson (1996) showed that the co-contraction of the TA and MF muscles occurred prior to any movement of the limbs. This suggests that these muscles anticipate dynamic forces which may act on the lumbar spine and stabilise the area prior to any movement. Hodges and Richardson showed that the timing of co-ordination of these muscles was very significant, and that back injury patients were unable to recruit their TA and MF muscles early enough to stabilise the spine prior to movement. The onset of the contraction before any force can act on the lumbar spine is essential for these muscles to act as stabilisers. Furthermore Hides et al (1996) found that the MF muscle showed poor recruitment in back injury patients, again showing how the recruitment of these deep trunk muscles is very important.
Interestingly, as early as the 1920's, Joseph Pilates talked about developing a 'girdle of strength', by learning to recruit the deep- trunk muscles. Even without a complete knowledge of anatomy and the benefits of the latest muscle activity research, he was very aware of the importance of these deep muscles and the supportive effect they produce.
Specificity of training
Having identified the key muscles and how they act, the next step is to establish how best to train these muscles. As with any type of strength and conditioning training, the training protocol for improving the function of the deep-trunk muscles must be specific to the task required. This specificity of training must take into account the type of contraction, the muscle fibre type and the anatomical position required.
By definition, the deep-trunk muscles act as 'stabilisers' and are not involved in producing movements, but instead involve static, or isometric, contractions. Furthermore, they must act as stabilisers continuously throughout everyday activities as well as fitness and sport activities, and so require very good endurance of low-level forces. These muscle do not need to be very strong, but they must be correctly co-ordinated and capable of working continuously. In addition, we want these stabiliser muscles to act by holding the lumbar spine in the neutral position, which is the correct alignment of the pelvis that allows for the natural S-curve of the spine. These characteristics underpin the following deep-trunk muscle training programme.
Core-stability training begins with learning to co-contract the TA and MF muscles effectively as this has been identified as key to the lumbar-support mechanism. To perform the TA and MF co-contraction you must perform the 'abdominal hollowing' technique with the spine in the neutral position. To do this use the following guidelines.
Start by lying on your back with knees bent. Your lumbar spine should be neither arched up nor flattened against the floor, but aligned normally with a small gap between the floor and your back. This is the 'neutral' lumbar position you should learn to achieve.
Breathe in deeply and relax all your stomach muscles. Breathe out and, as you do so, draw your lower abdomen inwards as if your belly button is going back towards the floor. Pilates teachers describe this as 'zipping up', as if you are fastening up a tight pair of jeans.
Hold the contraction for 10 seconds and stay relaxed, allowing yourself to breathe in and out as you hold the tension in your lower stomach area. Repeat 5-10 times.
Sounds easy? Well maybe, but it is absolutely vital that you perform this abdominal hollowing exercise correctly otherwise you will not recruit the TA and MF effectively. These coaching points must be followed to ensure your practice is correct.
l Do not let the whole stomach tense up or your upper abdominals bulge outwards, as this means you have cheated by using the large rectus abdominus muscle (the six-pack) instead of TA.
l Do not brace your TA muscle too hard; just a gentle contraction is enough. Remember it's endurance not max strength your are trying to improve.
l Do not tilt your pelvis nor flatten your back, as this means you have lost the neutral position you are trying to learn to stabilise.
l Do not hold your breath, as this means you are not relaxed. You must learn to breathe normally and maintain the co-contraction of TA and MF.
l Use your fingers for biofeedback on either side of you lower abdomen to feel the tension in the TA muscle.
Once you have mastered the abdominal hollowing lying on your back,practise it lying on your front, four-point kneeling, sitting and standing. In each position get your lumbar spine into neutral before you perform the hollowing movement.
The next step...
Having learnt to recruit the TA and MF muscles correctly in various positions, which can take anything from one session to one month or more, it is time to move onto simple core-stability exercises. These exercises may also involve the oblique muscles, other lumbar muscles and gluteals to assist the TA and MF in maintaining the lumbar spine in a stable neutral position. I have chosen two very useful examples, but there are many others included in Pilates lessons and used by trainers and physiotherapists that can be incorporated at this stage of core-stability learning.
Lying leg-lift stabilisation
Lying on your back with your knees bent. Ensure your back is in neutral. Place your hands on your hips for biofeedback.
Breathe in and relax. Breathe out and, as you do so, perform the abdominal hollowing or zipping-up action. Once you have established some TA tension, slowly slide your left leg out along the floor until it is straight and then slide it back. Your back should not have moved, and you pelvis should not have tilted as you performed this action. If your back or pelvis moved, you did not achieve the correct stability. Remember the coaching points from above, and ensure you follow them, otherwise you will jeopardise the training. Repeat for the other side 10 times each leg.
Variations include the same exercise with knee lifts up and knee drops out to the side. Again, the aim is to retain a stable lumbar spine in the neutral position as the legs move.
The waiter's bow
Stand up with good posture; knees soft, lumbar spine in neutral, head up and shoulders back and relaxed.
Breathe in and relax. Breathe out and as you do so perform the abdominal hollowing action. Keeping the tension, slowly lean forward from the hips 20 deg and stop, like a waiter's bow, keeping your back completely straight and long as you lean. Hold the lean position for 10 seconds - you will feel your TA and MF supporting you if you hold the correct position. Keeping the tension and the alignment, slowly return to your start position. Repeat 10 times. Again, remember the coaching points from above.
These exercises are two examples of learning how to keep the spine in neutral, using slow and controlled, static contractions of the trunk stabiliser muscles. Notice how technique is vital and the aim is to build up the time you are able to maintain good stability.
The ultimate aim of core-stability training is to ensure the deep-trunk muscles are working correctly to control the lumbar spine during dynamic movements, e.g., lifting a heavy box or running. Therefore it is important that once you have achieved proficiency of the simple core exercises, you must progress on to achieving stability during more functional movements. I have chosen two examples.
(1) The lunge
A classic exercise, but done slowly and with care it can teach you a great deal about body awareness and core stability. Interestingly, it is used by Alexander Technique teachers to help establish better movement patterns.
Stand with feet hip-width apart in front of a mirror. Ensure your lumbar spine is in neutral and your back is tall with your shoulders back and head up.
Lunge forward and bend your knee only half way down. Ensure that your front knee is in line with your toes and your back has remained upright with your lumbar spine in neutral and your hips level.
Push back up, initiating the movement by pushing down into the floor with your front foot. The force from your legs should bring you back up quickly and easily to your start position. Your back should have remained totally still and your hips level as you performed the push back.
Many people wrongly initiate the up movement by pulling their heads and shoulders back first; this extends the lumbar spine, losing the neutral position. Others have problems keeping their pelvis level while performing the lunge. You must learn to use your deep trunk and gluteal muscles to hold your lumbar spine in neutral and pelvis level as you perform the movement up and down. The movement should only come from the leg muscles.
(2) The press up
Another classic exercise, but more often than not it is performed with questionable core stability. Start from your knees - even if this means it is easy for your upper body - to learn the correct technique.
Your hands should be slightly wider that your shoulders and your head must be in front of your hands. Lift your hips so that there is a straight line from your knees through your pelvis and lower back, through your shoulders and all the way to your head. Ensure your lumbar spine is in neutral, using a mirror or a partner/trainer to help you. To maintain a neutral spine and a straight back during the exercise, the trunk muscles must provide active support. Slowly lower down, bending your arms all the way to the floor. Keep your head still with your neck straight relative to your back. Push up, initiating the movement by pressing down into the floor with your hands. Your back should remain still, straight and your lumbar spine in neutral throughout.
Many people allow their lumbar spine to arch and sag downwards as they perform the press up; this is because they are not using their trunk stabilisers enough to support the body.
These two exercises, used in a non-traditional manner, enable you to learn core stability while performing dynamic movements. By reducing the resistance - i.e., doing only half lunges and knee press ups - your are able to focus on the trunk stabilisers and achieving perfect technique rather than working the major muscle groups. The whole essence of core stability training is quality of movement and relaxation. The more you practise, the easier it becomes until you can control your lumbar stability at all times and during complex movements.
Hides et al. (1996). Spine. 21, 2763-2769.
Hodges and Richardson (1996) Spine. 21, 2640-2650.
Lewis et al (2000). International Journal of Sports Medicine, 1(4), November 2000.
Palastanga et al. (1994). Anatomy of human movement. Butterworth Heinemann: Oxford.
Richardson et al (1990). Physiotherapy, 36, 6-11.
Zatsiorski (1994). Science and practice of strength training. (1994). Human Kinetics: Champaign IL.