Continuing our research reviews by Dr Paul Batman

Dr Paul Batman is an international lecturer in Exercise & Sports Science degree and M.Sc programmes. With Andrew Richardson he started the Fitness Institute of Australia specializing in training fitness professionals.  He is currently consulting for educational institutions in curriculum design and writing educational materials.  His work is world famous and his ability to analyse deep scientific principles and bring them alive in simple application is second to none.  Join us for a series of writings by Paul.  If you have an area of interest and would like his view please do let us know.

Up Front

In recent times there has been an increased awareness of core stability exercise prescription. While it is important to have a strong trunk to perform many of life’s functions as well as sports activities is irrefutable, its role in the overall fitness program may have been over emphasised at the expense of other equally important fitness variables.

The role of the multifidus and transverse abdominis has been identified as a possible cause of potential low back problems, while the role of the abdominals has been stressed less.

This research review examines the validity of specific aspects of core conditioning and reports on its success in reducing the incidence of low back problems.

Keep Raising the Bar (Dr) Paul Batman

Research Review 1

Hides, J. A., Stokes, M. J., Saide, M., Jull, G. A., Cooper, D. H. (1993)

Evidence of Lumbar Multifidus Muscle Wasting Ipsilateral to Symptoms in patients with Acute/Subacute Low Back Pain

Spine; 19 (2): 165-172

Introduction

Stability and functional movement of the spine is largely controlled by the paraspinal muscles. However, in the case of spinal dysfunction, the role they play is not yet fully understood. An important muscle involved in stability is the lumbar multifidus. This is the largest and most medial lumbar back muscle. It originates from each lumbar vertebra to insert to the mamillary processes, the iliac crest and the sacrum. It is thought that muscle wasting associated with low back complaints is due to its disuse or atrophy possibly from associated pain. If this were the case then muscle size would be reduced over the entire length of the muscle that spans a number of spinal segments. Another possibility is that reflex inhibition can occur without pain and result in a more specific level of muscle atrophy. If this were the case then the level of muscle wasting would be seen below the vertebral level of the symptoms.

The purpose of this study was to investigate the cross sectional area and shape of the multifidus in patients with subacute and acute unilateral low back symptoms.

Method

Real-time ultrasound imaging was used to examine the effect of low back pain on the size of the lumbar multifidus muscle. 26 patients aged 17-46, with acute unilateral low back pain and 51 normal subjects aged 19-32 had bilateral scans performed. Multifidus cross sectional area (CSA) was measured from the 2nd to the 5th lumbar vertebra and in 6 patients S1 was also measured. In the normal subjects CSA was measured at L4 and in 10 subjects L2-L5.

Results

An obvious asymmetry of the multifidus muscle CSA was seen in symptomatic patients, with a smaller CSA recorded on the same side as that of reported symptoms. This occurred at only one vertebral level with a difference between sides of 31%. Above and below this level, between side differences were only 6%. A difference of only 5% was observed at all levels in normal patients. No correlation was found between the severity of symptoms and the degree of the muscle wasting. A more rounded muscle shape was seen in the patients compared to the normal subjects.

Applications for the Fitness Trainer

  1. It appears that a reduction in multifidus cross-sectional area occurs on the same side as that of the pain and symptoms experienced by the patients. This was detected by ultrasound imaging with muscle wasting only observed at the one vertebral level.
  2. The vertebral level at which the largest effect on muscle size occurred, was at the same level as that of the onset of pain. However the degree of muscle wastage was not related to the severity of the clinical findings.
  3. Hypertrophy of the multifidus muscle on the opposite side to that of the pain and the atrophied muscle did not occur.
  4. Muscle wasting occurred quite rapidly after the onset of pain and due to the localised nature of the wastage was not due to disuse of the muscle.
  5. Muscle wastage was more likely as a result of a reflex pathway of inhibition associated with perceived pain to prevent movement and therefore offer protection to the spine at that particular level. A metabolic effect was also likely to have contributed to the muscle wastage with a decrease in circulation due to muscle spasm.

Research Review 2

J.J. Crisco III., Panjabi, M. M. (1990)

The Intersegmental and Multisegmental Muscles of the Lumbar Spine – A Biomechanical Model Comparing Lateral Stabilising Potential

Spine; 16(7): 793-799

Introduction

The ligaments of the spine are what supports compressive loading. These ligaments have a critical load at which they can withstand and support before buckling will occur. Buckling occurs as a result of instability. It has been demonstrated that the load on the lumbar spine is twice that of body weight when standing relaxed depending on posture and stance. At loads less than body weight the ligaments of the spine are unstable, therefore the neuromuscular system must play a role in maintaining postural stability. A commonly talked about postural muscle involved in core stability is the multifidus, referred to as a stabiliser of the spine. The neck muscles have been described as ropes like that of a ship’s mast. The purpose of this study was to compare the lateral stabilising function of the lumbar spinal muscles. This study was the first to use the principles of mechanics in relation to stability of the spine depending on specific patterns of muscle positions and orientations (architecture).

Method

A biomechanical model was used to compare the stabilising function of the muscle architecture of the lumbar spine. An approximate value of the active and passive role of the stretch reflex as a spring of variable stiffness (stiffness proportional to activation) was used to evaluate the critical muscle stiffness needed for mechanical stability. The model consisted of two elastic systems, one representing the ligamentous spine and the other the passive and active properties of the muscles together with their stretch reflex. The load applied was the static body weight of the particular cross-section, one vertebra in thickness.

Results

The least efficient muscles at laterally stabilising the spine were the intersegmental muscles. Multisegmental muscles were more efficient at stabilising at any load. The greater the number of segments spanned the more efficient they became. The muscles that originated from the pelvis that spanned the maximum number of segments were shown to be the most effective in stabilisation. With increasing load on the spine, buckling is prevented most by the pelvic muscles and least by the intersegmental muscles. When a spinal segment is without muscle, the muscular model is proven to be unstable regardless of muscular stiffness.

Applications for the Fitness Trainer

  1. In all of the models used, the more lateral the location of the muscle to the spine, the greater the efficiency of stabilisation due to the increased moment arm to the line of muscle action.
  2. The most efficient muscles at stabilising in the frontal plane were those that spanned more than one spinal segment, with an increase in efficiency observed the more joints crossed.
  3. The muscles originating from the pelvis were 90% more efficient at laterally stabilising the spine than the least efficient of the intersegmental muscles. It appears that the larger the number of joints a muscle crosses, the more efficient it becomes.
  4. When an increase in critical load of the spine occurred buckling was prevented by increasing stiffness most efficiently by the muscles originating from the pelvis.
  5. When muscles were released from a vertebral body, instability occurred in all models under static body weight.

Research Review 3

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

Introduction

A high proportion of patients (60-80%) who have experienced an episode of low back pain have a recurrence of pain in the year following the initial episode. One important cause of this recurrence is the instability of the lumbar region. Instability is associated with muscle weakness, degenerative disc disease or injury. Muscles can control motion and provide segmental stabilisation. All the muscles that cross the lumbar area have the ability to provide stability of some sort. One of the more important muscles is the multifidus. Studies have shown this muscle to provide segmental stability by increasing segmental stiffness and controlling motion in the neutral zone. A relationship between the recurrence of low back pain after low back surgery and dysfunction of the multifidus muscle has been found. Even though pain usually subsides within 2-4 weeks of first experiencing low back pain, it is not understood whether multifidus recovery occurs also.

The purpose of this study was to investigate the recovery of the multifidus muscle after low back injury.

Method

All patients were experiencing their first episode of unilateral mechanical low back pain. After screening 41 patients were used in the study. 20 patients were allocated to group 1 (Control group – medical treatment only) and 21 to group 2 (medical plus exercise treatment). Assessments of pain, disability, range of motion and multifidus cross sectional area were undertaken weekly for 4 weeks. Examiners were independent and blind to the group allocation of patients. A further reassessment at 10 weeks also occurred.

Results

In group one (medical treatment only) the recovery of multifidus muscle was not automatic after painful symptoms had disappeared. However in group two, who undertook exercise therapy in addition to medical treatment, recovery of the multifidus was quicker and superior. All other measurements were similar between the two groups at 4 weeks. At 10 weeks following initial assessment, group 1 patients still had insufficient multifidus recovery.

Applications for the Fitness Trainer

  1. The multifidus muscle that are involved in stabilising the lumbar spine appears to not have an automatic and spontaneous recovery following a period of acute low back pain. This has important implications in the likelihood of a recurrence of the low back pain.
  2. The possible reason for this lack of recovery is due to reflex inhibition of the muscle at the point of injury or pain. This occurs as a result of sensory stimuli overriding voluntary muscle action. This results in muscle atrophy and weakness.
  3. Even when no pain is felt, reflex inhibition can still occur which appears to be the case in the patients in this study when no exercise therapy intervention was given. Ten weeks following the initial complaint, patients were fully weight bearing and completing normal duties with no pain, yet multifidus muscle recovery had not occurred.
  4. When specific localised exercises consisting of low intensity isometric contractions of the multifidus muscle are completed during recovery, multifidus function and size are both increased. The exercises allowed segmental innervation of the multifidus muscle together with contraction of the deep abdominal layer.
  5. This localised segmental level of training is very important in the initial stages of recovery, building a foundation for more general stabilisation exercises to follow that reinforce muscle control.

Research Review 4

Cholewicki, J., Panjabi, M. M., Khachatryan, A. (1997)

Stabilising Function of Trunk Flexor-Extensor Muscles Around a Neutral Spine Posture

Spine; 22: 2207-2212

Introduction

To maintain a mechanically stable equilibrium in the lumbar spine, a co-activation of antagonistic trunk muscles must occur. One way to think of these muscles is as guy wires that give stiffness to the intervertebral joints that they cross. The correct timing and coordination of these muscles is necessary however to effectively control spinal equilibrium and mechanical stability. A dysfunction may cause some low back complaints and chronic pain. The most important aspect of this stabilising function is during neutral posture when the spine has the least stiffness. A stable neutral spine must also be maintained over the entire day. Therefore because of lower levels of muscular activity in this position, the lumbar spine is most likely to buckle. This area has not been studied as yet without adding external loads. The purpose of this study was to verify that trunk flexor-extensor muscle co-activation exists in a neutral spine and that co-activation increases with added load providing mechanical stability.

Method

Ten subjects completed a series of flexion-extension tasks in a slow controlled manner. Six muscles: external oblique, internal oblique, rectus abdominis, multifidus, lumbar erector spinae and thoracic erector spinae were measured for activity using surface electromyography. Other simple spinal stability calculations were also performed. These were then compared to the results obtained.

Results

When no external load was applied to the neutral spine posture, the average antagonistic flexor-extensor muscle co-activation levels were 1.7% of maximum voluntary contraction (MVC). When an external load of 32kg was applied this level increased to 2.9% of MVC. In the inverted pendulum model no antagonistic co-activation was predicted based on static moment equilibrium, however when based on the criteria of mechanical stability, co-activation was 1.0% of MVC with no load and 3.1% with load (32kg). The stability model predicted 3.4% and 5.5% of MVC under the same conditions. This model simulated nil passive spine stiffness to simulate an injury.

Applications for the Fitness Trainer

  1. When all six muscles were examined individually, most of the subjects were able to maintain a constant level of activity of the internal obliques independent of trunk angle. A similar finding for the multifidus muscle was also observed in some subjects.
  2. Individual differences in the activation of the trunk musculature was to be expected due to the huge level of redundant behaviour of the neuromuscular system. This does allow the neuromuscular system to be extremely flexible and able to accommodate changes easily, unfortunately it also means it is very susceptible to dysfunction.
  3. From the results of the models used in this study, it can be said that the role of the trunk flexor-extensor muscle co-activation mechanism is to enable mechanical stability in the neutral lumbar spine.
  4. If axial loading is increased in the spine, it appears that the antagonistic muscle co-activation exhibited increases in response to the increase in load.
  5. If passive spine stiffness is reduced as in the case of some patients, then muscle co-activation must be increased to maintain spinal stability. This will most likely lead to fatigue of the muscles and subsequently pain will be experienced. It has been shown that with no passive spine stiffness and no external load, muscle co-activation was increased to levels that would be needed to carry a 32kg pack for the entire day!
  6. Therefore, increased levels of co-activation may be a useful indicator of spinal dysfunction in the passive stabilising system.

Research Review 5

Juker, D., McGill, S., Kropf, P., Steffen, T. (1998)

Quantitative Intramuscular Myoelectric Activity of Lumbar Portions of Psoas and the Abdominal Wall During a Wide Variety of Tasks

Medicine & Science in Sports & Exercise; 30(2): 301-310

Introduction

A major part of normal functioning of the lumbar spine is the role that the psoas muscle and the muscles of the abdominal wall have as dynamic stabilisers and movers. Past studies have used electromyographic (EMG) techniques to examine these muscles, however the deeper muscles, such as the psoas and the deeper abdominal wall have not been well documented. Muscular weakness or imbalance is quite often the cause of some low back problems, and therefore an integral part of many rehabilitation programs is the improvement of strength and endurance in the abdominal muscles. Of obvious importance is that minimal load is placed on the lumbar spine during abdominal training, due to the association between injury, posture and compressive loading. The psoas muscle has been shown to be a major cause of spinal loading. It has the greatest cross sectional area at the lower portion of the lumbar spine, however not much is known regarding its activity and mechanical capacity on the lumbar spine. The psoas is not a prime mover of the lumbar spine, but has the potential to stabilise and laterally flex the lumbar spine. The purpose of this study was to determine the involvement of psoas over a range of tasks that were challenging to the low back and hips.

Method

Five men and three women were recruited for the study. Intramuscular electrodes were inserted into the vertebral portion of the psoas and the three layers of the abdominal wall. Subjects then completed a range of clinical and rehabilitation tasks such as various forms of sit-ups, curl-ups, leg raises, side support, push ups, standing, sitting, lateral bending, hip rotation, lifting loads and holding loads. EMG data was recorded and amplitudes were normalised to maximum contraction efforts.

Results

Sit-ups of any type activated the psoas (15-35% MVC) more than curl-ups did (<10%MVC). Any barbell loads lifted up to 100kg did not overly activate the psoas. Push ups activated the psoas by as much as 25% MVC, whereas hip flexion exercises caused the most activation. An isometric side support exercise showed the least activation.

Applications for the Fitness Trainer

  1. It appears that the primary function of the psoas muscle is to flex the hip and that it does not have as much involvement in stabilising the lumbar spine as was thought. This was demonstrated in the barbell lifting exercises in which minimal psoas activity was recorded.
  2. It has often been said that psoas activity is lessened if the knees are bent during sit-ups compared to sit-ups performed with straight legs. This does not appear to be the case, as psoas activity as well as abdominal activity was high when sit-ups were performed in this manner.
  3. The isometric side support exercise appears to be the most effective method of training the oblique muscles with the least amount of psoas activation.
  4. If the aim is to increase muscular strength and endurance whilst minimises spinal loading, then a combination of curl-ups, cross curl-ups together with isometric and dynamic side support exercises are the best options.
  5. In any unstable spine, it is necessary to use any form of sit-up with caution (feet anchored). Both leg raises and sit-ups do not appear to challenge the abdominal wall very effectively but do produce higher levels of psoas activity

Research Review 6

Solomonow, M., Zhou, B., Harris, M., Lu, Y., Baratta, R. V. (1998)

The Ligamento-Muscular Stabilising System of the Spine

Spine; 23: 2552-2562

Introduction

It has been demonstrated using cadavers that the ligaments of the spine cannot maintain spinal stability in most routine loading tasks. If the muscles of the spine of a cadaver were removed, then only 2kg of load was could be tolerated before buckling occurred. It has also been shown through the stress and strain behaviour of the spinal ligaments that they only contribute a small amount of spinal stability during normal motion. Sensory receptors are located in all spinal ligaments. It has been demonstrated in cats that upon activation of these sensory endings, reflex activity of the paraspinal muscles occurs to help maintain spinal stability. It may be that the spinal ligaments are actually situated in specific locations that are sensitive to motion of the vertebrae in a range of planes of movement. This enables the monitoring of the movement by the receptors ultimately leading to activation of the musculature in a reflex manner. The purpose of this study was to investigate whether a reflex arc existed in the supraspinal ligament mechanoreceptors to the multifidus muscle

Method

Two types of subjects were used in this study. Three human subjects who were undergoing surgery due to deformations at L4-L5 were electrically stimulated in the supraspinous ligament at L2-L3 and L3-L4. Electromyography was conducted from the multifidus muscles at L2-L3 and L3-L4. The other subjects were 12 cats that were mechanically deformed in the supraspinous ligament from L1-L2 and L6-L7 in a sequential manner. Electromyography was conducted from all 6 levels. Two vertebrae were externally fixed to prevent motion. Loading of the ligament occurred before and after fixation.

Results

In two of the three patients, electromyograms were recorded bilaterally from the multifidus muscle indicating a direct relationship to the receptors of the supraspinous ligament. In the cat multifidus muscle, electromyograms were also recorded when mechanical loading of the supraspinal ligament at levels L1-L2 and L6-L7 was applied. The greatest electromyographic readings in the free-spine condition were at the level of the ligament damage. When two vertebrae were immobilised, the greatest activity was from the muscles at or one level above or below the immobilisation.

Applications for the Fitness Trainer

  1. In the spine, there appears to be a reflex arc of communication between the mechanoreceptors in the supraspinous ligament and the multifidus muscles. This is possibly activated when loads are applied to the supraspinous ligament that causes activation of the multifidus muscle at the level of the ligament loading, but also at one level above and below.
  2. A significant level of reflex activation of the multifidus muscles is reached when the stress in the ligament reaches a level that may cause great risk or rupture of the tissue. This most likely occurs at loads between 45 and 50% of an individual’s body weight.
  3. This reflex arc is most probably linked to other reflex arcs from other spinal ligaments and also from the discs and facet joint capsules. Other muscles other than the multifidus are likely to be involved also.
  4. The reflex action occurs when low to moderate loads result in motion of two vertebrae. This causes the multifidus muscles as high up as three levels above the loaded segment to be activated.
  5. The ultimate goal of this reflex arc is to maintain spinal stability. It would be advantageous that specific muscle strengthening exercises designed to target the relevant muscles such as the multifidus would help to improve spinal stability and act as a prevention to possible injury due to instability.

Research Review 6

McGill, S. M., Childs, A., Liebenson, C. (1999)

Endurance Times for Low Back Stabilisation Exercises: Clinical Targets for Testing and Training From a Normal Database

Archives of Physical & Medical Rehabilitation; 80: 941-944

Introduction

Exactly what are the structures that are most able to stabilise the back and which exercises are able to provide the necessary training effect to enhance their stabilising ability has been researched extensively. It has been found that the lumbar spine will buckle or become unstable when under pure compression, at substantially low levels of around 10 kilograms. The quadratus lumborum has been found to be the most recruited and activated muscle when spinal stability in this position is required. It was also found to be the most favourable in other tasks involving flexion and extension movements. The abdominals are still important stabilisers also, but less in the upright posture and when compression is high. Strengthening the quadratus would then be a beneficial part of any training or rehabilitation program. The question is how to effectively challenge this muscle while minimising the load on the lumbar spine. The “side bridge’ exercise has been identified as the best exercise to achieve this result, but what is the ideal contraction time and what is the endurance relationship between different sets of torso muscles?. The purpose of this study was to gather data on isometric endurance times during the “side bridge” and isometric flexion and extension exercises.

Method

Thirty one young healthy men and 44 young healthy women participated in the study. Four types of endurance tests of different exercises were completed in a random order. The exercises consisted of an isometric extensor and an isometric flexor exercise, a “side bridge” on both sides. 5 minutes of recovery was allowed between exercises. Endurance times were measured.

Results

Longer endurance times in the torso extension exercise were found in the women, but men showed a greater time period in the other exercises. Women held the “side bridge” exercise for 39% of their extensor time and 75% of their flexion time, whereas the men held it for 65% of extensor time and 99% of flexion time.

Applications for the Fitness Trainer

  1. This study was conducted due to the growing popularity of stabilisation exercises and the need to establish a norm database detailing endurance times for these isometric exercises.
  2. The establishment of the ratio of the endurance times of the tasks relative to each other is also needed by clinicians. These can then be utilised to help determine any endurance deficits in patients enabling the right program to be administered to achieve more normal function.
  3. As identified, the quadratus lumborum is the most dominant muscle involved in spinal stabilisation, therefore exercises to improve its capabilities is of benefit. However, core stabilisation exercises often also increased spinal loading to some extent and this may be contraindicated in some patients.
  4. The “side bridge” exercise has been found to be the best option in effectively training the quadratus muscle and the abdominal wall with minimum load applied on the spine, enhancing spinal stability.
  5. The endurance times the exercises were held for the study were for quantification purposes only and therefore in a real life clinical setting, the times the exercises would beheld for a shorter time period. The ideal contraction times and number of repetitions is a topic for further study.

Research Review 7

Granata, K. P., Marras, W. S. (2000)

Cost-Benefit of Muscle Co-contraction in Protecting against Spinal Instability

Spine; 25: 1398-1404

Introduction

The co-contraction of trunk muscles can aid in the protection of low back problems due to their effect in increasing spinal stability, yet their actual role in lifting mechanics and spinal injury is not well understood. When spinal load exceeds the tolerance level that the tissues can withstand, low back injury or pain can result. It has been estimated that vertebral tissues can withstand compressive loads up to 12,000N, with national standards advising avoiding compression levels greater than 6400N. In an unsupported spine however, the human spine will fail due to mechanical instability at loads less than 100N, indicating that failure in terms of stability can occur at loads that are actually considered safe in relation to tissue tolerance. Spinal stability is increased when muscle co-contraction occurs enabling greater loads to be withstood. However, an increase in spinal load will also occur due to the muscle co-contraction of the flexor and extensor muscles involved during lifting efforts. This increase in load will create a greater need for added stability, so the effects of muscle co-contraction must not be at a cost to spinal stability. The purpose of this study was to investigate the influence of trunk muscle coactivity on the stability of the spine relative to spinal load.

Method

Ten healthy men were studied during sagittal lifting tasks, trunk motion and reaction loads. Electromyographic activities of eight trunk muscles were recorded. A biomechanical model was developed to calculate spinal load and stability. Stability was defined in terms of the maximum spinal load that the system was able to stabilise. Spinal load and stability were measured as a function of the angle of trunk flexion and of co-contraction.

Results

A 12 to 18% increase in spinal compression occurred as a result of muscle co-contraction. A 34% to 64% increase in stability occurred. During trunk flexion, both spinal load and spinal stability increased.

Applications for the Fitness Trainer

  1. An increase in spinal stability occurs as a result of the coactivity between the trunk muscles. However this activity also adds to an increase in spinal load.
  2. There is a trade-off between the possibility of injury due to an increase in tissue load and the risk of spinal instability. The recruitment of muscle co-contraction is designed to balance out these risks.
  3. The model used in this study indicated that antagonistic co-contraction at lessor trunk moments may be beneficial and contribute to increased spinal stability such as in upright postures.
  4. When trunk moment was higher, such as in flexed postures, then antagonistic coactivity was lessened. This enabled the risk of spinal tissue overload injury to be reduced, as the stability was higher due to an increase in muscle force and stiffness.
  5. The increase in spinal compressive load as a result of antagonistic muscle coactivity of the trunk flexor muscles was estimated to be anywhere between 12 and 18%.

Research Review 8

Van Dieen, J. H., Cholewicki, J., Radebold, A. (2003)

Trunk Muscle Recruitment Patterns in Patients With Low Back Pain Enhance the Stability of the Lumbar Spine

Spine; 28: 834-841

Introduction

The recruitment patterns of the trunk muscles have been found to be different in patients suffering from low back pain (LBP). Previous studies have found significant differences between their findings that may be due to methodological differences. It may be that in patients with low back pain, trunk muscle recruitment patterns are altered as a compensation for a reduction in spinal stability. Previous studies have shown that an increase in activity can occur in static postures and standing with full trunk flexion. Also during the swing phase in walking when trunk muscles are not very active, an increase in activity in both the left and right extensor muscles was observed. These changes may be looked at as functional changes due to a reduction in spinal stability. However, an increase in the instability of the spine may cause excessive tissue strain and lead to feelings of pain. It has been shown in previous studies that an increase in spinal stability is attained through the co-contraction of trunk muscles. It is probable that the adaptation that occurs in low back pain patients is as a result of information received by both mechanoreceptors, this would then offer some explanation as to why the relationship to pain is not straightforward. The purpose of this study was to investigate trunk muscle recruitment patterns in patients with low back pain.

Method

Sixteen patients with low back pain and 16 control subjects all performed a series of slowly executed trunk movements around a neutral spine posture and isometric ramp contractions while sitting in the upright position. Electromyographic amplitudes and the estimated moment contribution ratios of antagonist over agonist muscles and also of the segmentally inserted muscles over the muscles inserting into the thorax and pelvis were only calculated. The effect that changes in muscle recruitment had on spinal stability was also studied using model simulations.

Results

Increased ratios of antagonist over agonist muscles and of the lumbar over the thoracic erector spinae muscles in electromyographic amplitude and moment contributions were recorded in the patients with low back pain versus the control subjects. An increase in spinal stability as a result of these changes was predicted in the simulation models used.

Applications for the Fitness Trainer

  1. The major finding of this study was that different trunk muscle recruitment patterns in patients with low back pain were found when compared to subjects who presented with no back pain.
  2. These differences are most likely brought about as in cases of low back pain there is usually some degree of associated spinal instability at one or more joints. To decrease this instability, muscles of the trunk must be recruited at a greater degree to compensate and offer better stability.
  3. A greater ratio of lumbar over thoracic erector spinae muscle activity as shown by EMG amplitudes occurred in the low back pain subjects. The corresponding ratios of the estimated moment contributions were also greater, giving evidence to greater muscle activity in the area of the reported pain. Greater ratios of antagonist over agonist muscles and their associated ratios of moment contributions were also greater in the patients.
  4. Even though this alteration in muscle recruitment has a positive effect on spinal stability, there may be a negative side also. The increase in activity as a result of muscle cocontraction may actually cause pain in the muscles leading to a catch 22 situation of pain-spasm-pain. Also the increased muscle activity increases the forces that act on the spine.
  5. When prescribing exercises as part of a rehabilitation program in patients with low back pain, caution should be used, with the aim to return the patient to a more normal muscle recruitment pattern.

Research Review 9

Huang, Q., Andersson, E., Thorstensson, A. (2001)

Intramuscular Myoelectric Activity and Selective Coactivation of Trunk Muscles During Lateral Flexion With and Without Load

Spine; 26(13): 1465-1472

Introduction

An increase in the risk of low back pain is often associated with manual type work in which asymmetric loading of the trunk is quite typical. Asymmetric loading can occur where the trunk is twisted, laterally flexed or loaded on one side similar to when an object is held in the hand. Movement of the spine and in particular stability of the spine is dependent on the coordination of the muscles surrounding it. Several muscles affect the movement and stability of the spine by producing torque by a mechanical advantage around the sagittal axis and at the same time having an affect on movement and stability in the frontal plane. The main lateral flexors are the rectus abdominis, internal and external obliques, psoas, quadratus lumborum and erector spinae. The role of the transverse abdominis is not fully clear but may be a key stabiliser. This deeper layer of the abdominal muscles appears not to be involved in compensation from direct loading of the trunk but more in a general stabilising effect for the lumbar spine.

The purpose of this study was to clarify the normal coordination patterns of the trunk lateral flexor muscles in particular to bilateral coactivation.

Method

Five men and one women average age 25 all physically active completed a series of maximal voluntary static contractions against a resistance to normalise EMG amplitudes. Two to three trials were conducted for each test with the highest EMG used for analysis. Participants completed static postures of erect standing and lateral bending to 15 and 30o to each side. Each position was held for 6s. Tests were repeated with a load of 20kg in one hand. EMG recordings were taken from the psoas, quadratus lumborum, transverse abdominis, lateral erector spinae, medial erector spinae, internal oblique, external oblique and rectus abdominis at the L3-L4 level.

Results

EMG data indicated that all of the muscles on the contralateral side to the side of lateral flexion exhibited the highest readings during loaded lateral flexion at the most laterally flexed position (with the exception of the rectus abdominus). The ventral muscles showed a greater degree of bilateral coactivation then the dorsal muscles.

Applications for the Fitness Trainer

  1. Activity increased overall in most of the ventral and dorsal muscles on the contralateral side to the side of lateral flexion and lateral flexion with added load. The ventral muscles on the ipsilateral side also exhibited an increase in activity that lead to an increased level of bilateral co-activation of those muscles, however this was greater in the unloaded condition.
  2. The highest EMG activity levels were recorded for the contralateral external oblique during the tasks completed. The lowest activation levels in the abdominal group were observed in the rectus abdominis. This muscle group also showed the least adaptation to a change in trunk angle and load. This could be due to the external oblique possessing the longest lever arm and the rectus abdominis the shortest, relative to a sagittal axis of rotation. This causes a reduced mechanical advantage.
  3. The contralateral transverse abdominis had a high level of activity that tended to increase with trunk lateral flexion in both the loaded and unloaded conditions. The function of the transverse abdominis is primarily associated with increasing intra-abdominal pressure due to its horizontal muscle fibre direction and encouraging it to help stabilise the spine.
  4. During twisting type movements, the transverse abdominis has also been shown to have a mechanical type role in torque production. Both the left and right portions of the muscle showed an alternating pattern when trunk twisting occurred.
  5. Abdominal muscle co-contraction has been reported from modelling studies to have a possible affect on lumbar spine stability. It appears that the abdominal muscles may be more important in this respect than the dorsal muscles. A less stable spine during asymmetric loading may be the result of a dysfunction of the abdominal muscles and can possibly lead to injury.

Research Review 10

Nadler, S. F., Malanga, G. A., Bartoli, L. A., Feinberg, J. H., Prybicien, M., Deprince, M. (2001)

Hip Muscle Imbalance and Low Back Pain in Athletes: Influence of Core Strengthening

Medicine and Science in Sports and Exercise; 34(1): 9-16

Introduction

The influence of core conditioning on the prevention of injuries to the spine and extremities has become very popular in many sports training programs. The key component to core conditioning is the strengthening of the abdominal, spinal and gluteal muscles with the intention of increasing stability and control during sporting or daily activities. The importance of stabilisation of the pelvis has been shown in past studies. A reduction in low back pain has also been indicated with increased abdominal strength and increased core stability.

The purpose of this study was to investigate the effects of a core conditioning program on the incidence of low back pain and on the strength balance of the hip musculature.

Method

From 1998-2000 NCAA Division 1 collegiate athletes had their hip strength measured during pre-participation physical examinations. Low back pain (LBP) incidence was monitored throughout the year. Following these physical examinations, the athletes were given a structured core conditioning program consisting of abdominal, spinal and hip extensor strengthening exercises. The occurrence of low back pain and the relationship to hip muscle imbalance was assessed between consecutive years.

Results

No significant difference in the occurrence of low back pain was observed following the administration of the core strengthening program. No difference was seen in the side-to-side extensor strength between the athletes from 1998-1999 and 1999-2000 in the physical examinations. Right hip extensor strength in comparison to left hip extensor strength was stronger following the core conditioning program. Some gender specific differences were observed after core strengthening.

Applications for the Fitness Trainer

  1. In terms of reducing the incidence of low back pain in college male athletes, no difference was observed following the implementation of a structured core strengthening program which focussed on strengthening the muscles of the trunk, spine and hip extensors.
  2. The core strengthening program may have had an influence on the dynamics of side-to-side hip strength though. Side-to-side hip strength appeared to increase following core strengthening. This may be of benefit to reducing the risk of low back pain in the future.
  3. In females, no difference in the occurrence of low back pain was observed following the core strengthening program. In fact, the incidence actually increased slightly. It may be that a more specialised program emphasising hip abduction strengthening may be required in female athletes.
  4. These results are in conflict with other studies and the latest understanding that core conditioning and abdominal training, especially strengthening of the lower abdominals should actually decrease the likelihood of low back pain. It may be that the subject numbers were too small in this study

Bottom Line

1. It appears that a reduction in multifidus cross-sectional area is found on the same side as that of the pain and is experienced by the patients with low back pain symptoms. It appears the more lateral the location of the muscle to the spine, the greater the efficiency of stabilisation due to the increased moment arm to the line of muscle action. The most efficient muscles at stabilising in the frontal plane were those that spanned more than one spinal segment, with an increase in efficiency observed the more joints crossed.

2. A high proportion of patients (60-80%) who have experienced an episode of low back pain have a recurrence of pain in the year following the initial episode. One important cause of this recurrence is the instability of the lumbar region primarily associated with muscle weakness, degenerative disc disease or injury.

3. The role of the trunk flexor-extensor muscle co-activation mechanism (both contracting at the same time) is to enable mechanical stability in the neutral lumbar spine. The increase in spinal compressive load as a result of antagonistic muscle coactivity of the trunk flexor muscles and is estimated to be anywhere between 12 and 18%.

4. It appears that the primary function of the psoas muscle is to flex the hip and that it does not have as much involvement in stabilising the lumbar spine as was once thought.

5. It has also been shown through the stress and strain behaviour of the spinal ligaments they only contribute a small amount of spinal stability during normal motion. Sensory receptors are located in all spinal ligaments. In the spine, there appears to be a reflex arc of communication between the mechanoreceptors in the supraspinous ligament and the multifidus muscles. This is possibly activated when loads are applied to the supraspinous ligament that causes activation of the multifidus muscle at the level of the ligament loading, but also at one level above and below.

6. A significant level of reflex activation of the multifidus muscles is reached when the stress in the ligament reaches a level that may cause a greater risk or rupture of the tissue. This most likely occurs at loads between 45 and 50% of an individual’s body weight.

7. It has been found that the lumbar spine will buckle or become unstable when under pure compression, at substantially low levels of around 10 kilograms. The quadratus lumborum has been found to be the most recruited and activated muscle when spinal stability in this position is required. It is also used favourably in other tasks involving trunk flexion and extension movements.

8. The contralateral transverse abdominis has a high level of activity that tends to increase with trunk lateral flexion in both loaded and unloaded conditions. The function of the transverse abdominis is primarily associated with increasing intra-abdominal pressure due to its horizontal muscle fibre direction and encouraging it to help stabilise the spine. This muscle works closely with the multifidus in stabilizing the spine.

9. In terms of reducing the incidence of low back pain in college male athletes, no difference has been observed following the implementation of a structured core strengthening program that focussed on strengthening the muscles of the trunk, spine and hip extensors.  This type of core strengthening program may have an influence on the dynamics of side-to-side hip strength. Side-to-side hip strength appeared to increase following core strengthening. This may be of benefit to reducing the risk of low back pain in the future.

10. Different trunk muscle recruitment patterns are apparent in patients with low back pain when compared to patients who present with no back pain.  These differences are most likely brought about to some degree by associated spinal instability at one or more joints. To decrease this instability, abdominal muscles must also be recruited at a greater degree to compensate and offer greater stability. Spinal stability is a function of an increase in strength of the multifidus, transverse abdominis and the other abdominal muscles.

Quiz – test your knowledge

  1. An important muscle involved in stability is the lumbar multifidus. This is the largest and most lateral lumbar back muscle.
  2. At loads greater than body weight the ligaments of the spine are unstable forcing the neuromuscular system to play a role in maintaining postural stability.
  3. When specific localised exercises consisting of low intensity isometric contractions of the multifidus muscle are completed its function and size are both reduced.
  4. The most important aspect of stabilization in neutral posture is when the spine is at its least stiffness
  5. The psoas is not a prime mover of the lumbar spine, but has the potential to laterally flex the lumbar spine.
  6. The “side bridge” exercise has been found to be the best option in effectively training the quadratus muscle and the abdominal wall with minimum load applied on the spine, enhancing spinal stability.
  7. There is a greater ratio of lumbar over thoracic erector spinae muscle activity in patients with low back pain.
  8. The contralateral transverse abdominis contracts with significant force in trunk lateral flexion in both the loaded and unloaded conditions.
  9. In terms of reducing the incidence of low back pain in college male athletes, no difference has been observed following strengthening the muscles of the trunk, spine and hip extensors.
  10. In the spine, there appears to be a reflex arc of communication between the mechanoreceptors in the supraspinous ligament and the multifidus muscles.