Chapter 7 Changed control of posture and movement

the dysfunctional state

Cholewicki and van Dieën ¹ comment that while there is an emerging consensus in the literature that muscle activation patterns are different in people with back pain, the interpretations of these findings are divergent. By and large the scientific community has little considered whether altered motor control might be significant in causing back pain.

Some 30 years ago Janda,^2,³ Lewit⁴ and others in the Prague school of manual medicine introduced the concept of ‘functional pathology of the motor system’ to explain the development and perpetuation of pain in the musculoskeletal system. Some more recent studies have implicated pre existing functional changes in the development of later pain⁵^–⁸ or in the recurrence of low back pain.⁹

Functional pathology of the motor system ²

Excluding insidious pathology, Janda ² considered that most musculoskeletal pain syndromes are the result of impaired motor system function. This functional pathology of the motor system and its interactions with the whole organism, mainly of a reflex nature,³ is regularly involved in many organic diseases and underpins most spinal pain and related disorders.

In essence, the motor system comprises three functionally interdependent systems. Dysfunction in any one system will influence function in the other systems, perpetuating further impairment. A pattern generating mechanism can be set in train. The systems are:

• The corticosubcortical motor regulatory centers of the CNS. Phylogenetically the youngest and most fragile part of the motor system. Impaired function at this level results in defective and uneconomical movement patterns,¹⁰ poor adjustment of fine movements, and the progressive switch from complicated movement patterns to the more primitive ones regulated at the subcortical level.²

• The muscle system. This represents perhaps the most exposed part of the motor system, having to ‘extensively respond to changes due to civilization or more exactly to the technicalization of our living conditions’.¹¹ As the main movement effectors, they must respond quickly to all stimuli coming from the neural system, reacting to changes in the periphery especially from the articular system.² Clinically, evident changes in the muscle system are generally apparent for some time before the onset of pain. The presence of pain further compounds the muscle dysfunction creating further change throughout the whole motor system.

• The articular system. The welfare of the joints is dependent upon balanced neuromuscular control. ‘Joint dysfunctions are only one expression of impairment of motor system as a whole i.e. of both neuromuscular and osteoarticular systems’.³ Further, any changes in the joints will be reflected in changes in both the neural and muscle systems.

Motor control impairments precede the onset of pain

The quality of muscle function depends directly on the central nervous system activity.¹² While functional impairment of the motor system is the most frequent cause of pain in the motor system it is not identical with pain and may remain clinically silent. Depending upon the primary locus, the impairment is generally clinically discernable either in palpable changes at the spinal joint and observable changes in movement patterns, the early onset of fatigue and faster switch into more primitive movement patterns in fatigue of the motor system.² Gregory et al.⁷ demonstrated altered motor control characteristics that can distinguish the likelihood of an individual developing back during common tasks such as standing.

Significantly, Janda says, ‘the high incidence of functional impairment makes it extremely difficult to estimate the borders between the norm and evident pathology’.²

According to Janda,² the development of impairment follows two basic rules as follows:

1. The rule of vertical generalization. A local impairment, for instance in a joint, provokes reaction and adaptation processes in all other parts of the motor system i.e. in the muscular or neural system. Similarly, any alteration in motor regulation as in stress, depression and neurotic reactions involves simultaneously and preferably the muscles and then the joints. In this respect, the limbic system has particular relevance in motor control.

2. The rule of horizontal generalization. Impaired function in one joint or muscle provokes a reaction and adaptation in related other joints or muscles and spreads so that finally the whole system, articular or muscular will be involved. This is particularly evident in the axial spine and proximal limb girdles. Restriction of a spinal segment or a number creates relative flexibility at adjacent segments. A stiff hip joint creates a compensatory relative flexibility ¹³ in the low back. Clinically it is common to see the coexistence of back pain with a plethora of other overt or covert symptoms such shoulder and neck symptoms, hip and knee pain etc.

A local pain symptom is generally the expression of a regional and general neuromyoarticular problem.

Importantly, recognizing the significance of these ‘rules’ allows the clinician to predict the development of functional impairments and introduce prophylactic and rational therapeutic interventions.

The muscle system mirrors the state of sensory motor integration

Movement patterns are one of the basic elements of movement. The patterning process is the most important way that movement develops. According to Janda,¹⁴ these involve a chain of conditioned and unconditioned reflexes which are constant over a short period of time but change, sometimes considerably, over life. Changes occur in response to changing conditions of the ‘inner milieu’ as well as the outer environment. ‘The degree of activity and time synchronization of various muscle groups within the movement are thus characteristic of such patterns’.¹⁴

Hodges ¹⁵ remarks that with regard to lumbopelvic pain, ‘two relatively consistent research findings have been observed: increased activity in the superficial muscles and decreased activity of the abdominal canister’.

Clinical observation of patients with spinal pain syndromes, supported in part by frank and extrapolative research findings, demonstrates changes in the typical activation patterns and altered functional roles of muscles in each of the two proposed principal muscle systems. This results in imbalanced activity between the two systems which is reflected in altered motor control responses to perturbation and for organizing body alignment, postural control and movement.

In time this leads to structural changes and changes in other co-dependent systems.

Altered qualities of function in each muscle system

Conceptually and generally speaking, we tend to see a change in the timing and level of activity – too little activity and more phasic activity in the deep system and too much, more tonic activity of certain muscles in the superficial system. However, muscles in the deep system can be overactive and those in the superficial system underactive.

Systemic local muscle system (SLMS; see Ch.5)

Altered responses which variably occur in muscles classified within this system as muscles of the SLMS demonstrate:

• Delayed feedforward postural responses have been demonstrated in transversus abdominus,^16,¹⁷ internal oblique and transversus,¹⁸ internal oblique, multifidus and gluteus maximus.¹⁹ Transversus activity changes from direction independent to direction specific activity in the control of reactive forces of the trunk.¹⁶ Mok et al.²⁰ found decreased preparatory movement of the lumbopelvis and increased corrective movements in response to perturbation from rapid arm movement.

• Inadequate. Relative underactivity, inhibition, weakness has been shown in the abdominals;¹⁸ transversus abdominus;²¹ multifidus;^22,²³ the diaphragm.²⁴ Functionally they act like ‘shy muscles’. Also, arthrogenic inhibition, e.g. of multifidus due to pain or directly impaired proprioception of an injured joint is clinically common. Isolated segmental wasting of multifidus ipsilateral to symptoms has been shown.²⁵ Simulated microgravity/spinal un-loading/bed rest studies have also shown selective atrophy of multifidus.²⁶

• Diminished patterns of coactivation in the SLMS affect spinal support and control mechanisms. O’Sullivan et al.²⁴ found poor coactivation of the diaphragm and pelvic floor in subjects with sacroiliac pain. During the active straight leg raise test diaphragm splinting, respiratory disruption and pelvic floor descent occurred.

• Muscle system activity is poorly sustained. Low load sustained postures become difficult as the more usual SLMS tonic yet variable activity becomes more phasic. Subjects with back pain have also demonstrated more phasic activity in transversus while walking ²⁷ and a shift from locomotor to primarily respiratory activity.²⁸

Systemic global muscle system (SGMS)

In conjunction with the changed activity in the SLMS, altered timing and degree of activation occurs inversely in muscles within this system as follows:

• Early onset of activity precedes SLMS muscles.¹⁹ This means that these muscles are activated from a non stable, poorly controlled foundation tending to create yanking stresses within the axial skeleton.

• Muscles within this system become variably overactive and dominant in movement patterns^7,²⁹ irrespective of pain.³⁰ In the presence of underlying irritable segmental joint restrictions and/or frank pain they are predictably overactive. Normal studies have indicated that these muscles become more active in situations involving reduced gravitational loading and related decreased sensory input.^31,³²

• These muscles are easily strengthened, hypertrophy and become tight and short³³ – the functional ‘bullies’, they are generally over active and those that everyone is obsessively stretching!

• SGMS muscles become more tonically active rather than phasic, a changed role from phasic activity to more tonic activity as the system becomes co-opted into a more postural role.³⁴ When abnormally activated for antigravity control³⁵, the patient ‘holds himself up’ against gravity rather like scaffolding holding up a building. He then often can’t voluntarily let them go, particularly around the body’s centre of gravity, and evidenced in a lack of the flexion–relaxation response seen in many people with back pain.^36,³⁷ Muscles such as external oblique and thoracic erector spinae form part of this system.³⁸

In general terms, Janda ³⁹ considered that at least five types of increased muscle tone can result from either:

• Dysfunction of the limbic system

• Impaired function at the segmental (interneuronal) level

• Impaired coordination of muscle contraction (trigger points)

• As a response to pain irritation

• Overuse of the muscles – this is as a rule combined with changed elasticity of the muscle and usually described as muscle tightness.

Muscle imbalance

Janda proposed that clinically developed imbalance between different muscle groups was probably the result of both reflex and mechanical mechanisms.³ He was initially more interested in the effect of the tight overactive muscles (SGMS) and their inhibitory action upon their antagonists e.g. overactive erector spinae may inhibit abdominal activity.³ Stretching and other inhibitory techniques applied to the tight muscles often spontaneously improved the weakened antagonist. With respect to the imbalanced muscle system response, he questioned whether there was any difference of innervation between the two systems and noted that the tight muscles were often those involved in flexor reflexes and those with a tendency to be underactive or weaken were those mainly participating in extensor reflexes.³ Importantly, pain, injury, fatigue or stress and the working out of new movement patterns tends to reduce activity in the SLMS and increase activity in the SGMS.

Clinically, in the dysfunctional state, a reciprocal relationship evolves whereby reduced deep system activity necessitates the adoption of more superficial system strategies, which in turn inhibits or disallows effective deep system activation. The dysfunction becomes reinforced, perpetuated and entrenched.

The poorly coordinated activity between the two muscle systems creates muscle imbalance throughout the body. This can occur in a number of ways:

• Between the two systems which begin to work counter to one another instead of in a mutually supportive relationship

• Within each system, particularly the SGMS e.g. between the rectus femoris and hamstrings

• Between the axial flexor and extensor systems.

When overactive, the global muscles of the trunk can act to shorten, compress and constrict parts of the torso acting rather like very tight outer clothing, while the behavior of the SLMS resembles loose old underwear!

Imbalanced activity between the two muscle systems: direct ramifications for underlying control of NPRM

Research interest is increasingly concerned with the quality of postural and movement control in the presence of back pain. However, to date, Dankaerts et al.⁴⁰ are one of the few who have suggested that inherent postural control faults may predispose one to the development of pain syndromes.⁴⁰

The main features of dysfunction in the postural reflex mechanism can be summarized as:

• Reduced endurance in antigravity posture and movement because of poorly organized and sustained synergies of low grade tonic activity from muscles within the SLMS. While some studies have shown that people with chronic back pain develop a higher ratio of fast to slow twitch fibres and extensor muscle activity becomes more phasic,⁴¹ it is suggested that clinically this inability to organize appropriate patterns of underlying response also contributes to reduced staying power in movement.

• Reduced, imbalanced and delayed patterns of SLMS coactivation affects joint protection and control of spinal support mechanisms such as low load IAP; jeopardizes effective weight shift and appropriate adaptive postural presetting of the limb girdles necessary to facilitate the ensuing pattern of movement. Ineffective deep system coactivation diminishes effective SGMS activity.

• Effective postural control and precisely coordinated and discrete movements are highly dependent upon adequate proprioception. Diminished proprioception in subjects with back pain has been reported.^42,⁴³ Taimela et al.⁴⁴ found reduced ability to sense rotational position change in the lumbar spine when sitting, particularly when fatigued. O’Sullivan et al.⁴⁵ found significant deficits when patients attempted to reposition the lumbar spine into a neutral lordosis when sitting. Postural and gait stability is reduced in astronauts following in-flight adaptation of CNS processing of altered sensory inputs from the vestibular, proprioceptive and visual systems.⁴⁶ Bed rest studies involving reduced antigravity sensory input demonstrate reduced activity in certain SLMS muscles particularly the one joint extensors^26,⁴⁷ and increased activity in certain SGMS muscles.^31,³²

• Poorer balance has been found with greater postural sway,⁴⁸ the predominant use of the hip strategy over the ankle strategy.⁴⁹ Mok et al.⁵⁰ found inability to initiate and reduced control of the hip strategy for balance. Conversely, increased trunk muscle stiffening has been shown to degrade postural control⁵¹ as it limits adaptive segmental adjustments. This has been shown in sitting⁵² and particularly so in the sagittal plane.⁷²

• Disturbed motion patterns become more stereotyped and show predictable change in kinematics e.g. back pain subjects used increased lumbar flexion when forward bending.^9,^53,^54,⁶⁷

• Variably increased patterns of SGMS co-contraction act to splint some regions of the spine. Reduced postural support from the deep system and increased SGMS activity leads to the adoption of coarse central holding or ‘cinch’ patterns in posture and movement. These have also been described by O’Sullivan as fixing and splinting strategies.^24,²⁹ Radebold et al.⁵⁵ found increased co-contraction of the superficial trunk muscles in response to multidirectional sudden load release while subjects were generating isometric forces of 20%–30% maximal exertions. SGMS activity typically increases with load, exertion and speed. Incidentally subjects were semi seated and the pelvis was restrained allowing no postural adjustment of the pelvis in controlling the perturbation to the torso – hardly a functional pattern and co-contraction can be expected. Gregory⁷ found greater responses of the superficial trunk extensors and flexors in response to unexpected perturbations in subjects who developed back discomfort when standing for 2 hours. After 8 weeks of bed rest simulating a microgravity environment, Belavey et al.³² found increased activity but decreased co-activation of the superficial lumbopelvic muscles in stabilizing the pelvis during a repetitive leg movement. Clinically, patterns of both increased and decreased SGMS co-activation are found and better understood when patients are sub grouped into the two principal clinical pictures. This helps explain the variance in the various research studies (see Ch. 9).

• Altered performance of other functionally related systems such as continence, breathing and cardiovascular deconditioning. Studies by Smith ⁵⁶ have shown that people with respiratory disease and incontinence have increased activity of the superficial trunk muscles, restricted rib expansion and diaphragm descent.

Further findings in back pain research influencing motor control

Muscle fatigue

The subject of fatigue has attracted a lot of research interest. Enoka ⁵⁷ describes fatigue as ‘the activity related impairment of physiological processes that reduce muscle force… after the onset of sustained physical activity’. Fatigue involves a variety of elements throughout the motor system and Neumann⁵⁸ suggests it is useful to consider fatigue as primarily occurring centrally or peripherally. Central fatigue can involve the limbic system, activation of the primary motor cortex, or descending CNS control over neurons and motoneurons in the spinal cord. Peripheral fatigue relates to neurophysiologic factors related to action potential propagation in motor nerves and transmission of activation to muscle fibres.⁵⁸ Normally the nervous system compensates for muscle fatigue by either increasing the rate of activation or recruiting assistive motor units thereby maintaining a stable force level.⁵⁸ Slow twitch motor units can sustain an isometric force longer than fast twitch. Slow twitch muscle can sustain a greater force during isovelocity shortening contractions, while fast twitch muscle is able to sustain greater power production.

Janda ⁵⁹ maintained 40 years ago that fatigue increased the differential timing and activity level in the two muscle systems adversely affecting coordination and the quality of the motor patterns (see Ch.5).

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