From the biological perspective, a whiplash injury can result in trauma to any of the cervical articular, ligamentous, muscle, nerve, or vascular structures.1–3 The injury results in both biological and psychological reactions, which can range from minor to major responses. From a biological perspective, and like trauma to any other regions of the musculoskeletal system, the injury results in pain, loss of motion, and impaired neuromuscular function, which impacts on functional activities, work, and quality of life. Physical activity and therapeutic exercise are mainstays for management of musculoskeletal injury and pain of both the spine and extremity joints.
Current clinical practice guidelines for the management of whiplash-associated disorders advocate exercise in association with assurance and advice to resume normal activities as tolerated as a first line approach in both the acute and chronic states.4,5 Active treatments in the main have been shown to be more effective than advice to act as usual only, in the acute and subacute states.6–8 In accordance with the guidelines, both recent research syntheses9–11 and systematic reviews12–14 point to benefits of physical rehabilitation programs inclusive of exercise and manual therapy for pain relief and improved function in the management of both acute and chronic whiplash-associated disorders. However, the sparse number of high quality trials limits the strength of conclusions11,14 and effect sizes of treatments are modest.12
Physical rehabilitation has an important role in the management of whiplash-associated disorders not only to help decrease symptoms but to reestablish cervical movement and sensorimotor function to permit the person to safely resume normal functional activities. Reestablishing movement and sensorimotor function would seem fundamental to the pursuit of decreasing the incidence of transition of acute whiplash to chronicity or to recurrent episodic pain. As with any medical or psychological intervention, physical rehabilitation has not proven to be the panacea for all whiplash-associated disorders and there are several issues to consider toward enhancing effectiveness. One major issue is the construct of a therapeutic exercise program. As systematic reviews reveal, many different forms of exercise have been tested in the clinical trials of patients with whiplash-associated disorders, yet the indications or rationale for a particular exercise approach are often unclear. Prescription of an exercise intervention should ideally aim to reverse identified impairments that are associated with an individual's neck pain and functional disability. Toward construction of an appropriate, research-informed exercise regime, the nature of impairments in cervical movement, and muscle function that have been found to present in whiplash-injured persons will be briefly reviewed. Research into disturbances in movement and muscle behavior, in association with neck pain and injury, is increasing and the resultant knowledge has the potential to direct exercise programs more precisely. In addition, some of the challenges in implementing an effective exercise program will be highlighted toward the aim of lessening the transition of acute whiplash to a chronic disorder.
DISORDERED NECK MOVEMENT
Loss of active range of neck movement impacts on daily functional activities and is a well documented sequel of a whiplash injury in both the acute and chronic states.15,16 The magnitude of loss is variable and appears to be associated with pain severity17 and by inference, injury severity. Movement restriction is apparent in both primary and conjoint motion.18 Nevertheless, it is not only the range of movement that is affected. More recent research has also documented pathological movement patterns in subjects with whiplash-associated disorders, which can impair function and an individual's ability to participate normally in everyday activities. These include reduced acceleration and velocity of neck movement, reduced smoothness, and irregular axes of neck movement.15,19–22 Neither actively seeking compensation nor fear avoidance beliefs seem to play a role in either the presence or magnitude of these disturbances.19,22 Moreover, the disturbances do not appear to be a conscious, volitional strategy. In a novel design, Baydal-Bertomeu et al15 recruited subjects who had fully recovered from a whiplash injury and asked them to perform the head movement tasks (acceleration and velocity) as they would have done when they were in pain. These subjects feigning pain responded quite differently and had significantly more gross disturbances than either the whiplash or control cohorts.
Not unexpectedly, variability is present between subjects with whiplash-associated disorders in the degree of movement loss as well as in the presence or not and the magnitude of movement disturbances.21 Pain intensity (and its impact on proprioception and fusimotor activity23) seems to be a major variable that relates to the presence and degree of impairments.17,19,22
Range of motion exercises have long been included in therapeutic exercise regimes but there has not been a specific emphasis on rehabilitation of deficits such as reduced movement velocity, quality, and control. Their inclusion in an active movement exercise regime could enhance movement functionality. The individuality in the nature of movement disturbances emphasizes the importance of developing individualized rehabilitation programs for specific dysfunctions in the aim of providing appropriate rehabilitation toward the prevention of transition to chronicity.
ALTERED MUSCLE BEHAVIOR AND MUSCLE PROPERTIES
There is a growing body of research which shows that neck pain and injury result in widespread changes in neuromuscular control strategies and muscle properties (see review, Falla and Farina24). Changes are evident in both the cervical and axioscapular musculature. As in every other region of the body, maintenance of good joint health is reliant on appropriate muscle function. The number of muscles acting on the cervical spine together with its capacity for multiple degrees of freedom means that specific forces may be produced or resisted by several combinations of muscle actions. Nevertheless, there is some functional specificity within the neck muscles, which has implications for designing therapeutic exercise programs for appropriate rehabilitation. In general, the superficial flexor and extensor muscles with their longer lever arms and greater cross-sectional areas have greater torque-producing capacities than their deeper counterparts and are important for movement and support of head load.25,26 In contrast, the deeper muscles are smaller and have less torque-producing capacity. For example, the deep longus capitis and colli provide only 17% of the flexion torque with the remainder being supplied by sternocleidomastoid and anterior scalene muscles.26 The deep muscles have segmental attachments, larger spindle densities, and muscle fiber compositions that enable them to guide and support the cervical motion segments.27–29 It has been shown experimentally, that activity in the superficial muscles without deep muscle activity will lead to segmental buckling.30 Thus rehabilitation programs must ensure that the capacity of all muscles is adequately rehabilitated.
The changes in the cervical muscle system with whiplash-associated disorders are in the main, not unique and are also found in patients with idiopathic neck pain.31,32 In relation to neuromuscular changes, pain and injury result in the reorganization of motor control strategies. Changes have been demonstrated in muscles′ spatial and temporal relationships. In the cervical extensor group, there is initial evidence of reduced performance of the deep cervical muscles (multifidus/semispinalis cervicis), but not of the more superficial extensors as measured (magnetic resonance imaging) in a standard muscle test in patients with chronic neck pain compared with control subjects.33 The spatial relationships of the deep (longus capitis and colli) and superficial flexor (sternocleidomastoid, anterior scalene) muscles are altered in association with neck pain disorders. Activity in the deep cervical flexor muscles is reduced and is associated with heightened activity in the superficial cervical muscles.32,34,35 Changes are also evident in the muscles′ temporal behavior with the neck flexor muscles (most significant in the deep neck flexors) losing their feedforward activation in response to perturbations induced by arm movements.36,37 The significance of impaired deep muscle activity for the support and control of injured or pathological cervical segments is appreciated when considering the functional specificity of the neck muscles in control of head posture and load as well as the strains and loads induced on the cervical segments with upper limb function.38,39 There are also changes in feedback mechanisms as in evidence with disturbances in cervical kinesthetic sense, eye movement control, and balance which commonly occur in association with whiplash-associated disorders.40–43
In relation to the higher levels of activity in the superficial muscles, increased coactivation of the neck flexors and extensors has been shown with experimental neck pain44 as well as in functional tasks (e.g., typing) in persons with neck pain.45 As well, changes in patterns of trapezius activity have been recorded during functional tasks in persons with whiplash-associated disorders.46–48 Such changes in activation levels again has implications for adverse loading on cervical structures. There can be other possible functional ramifications of this increased muscle activity as reflected in the change in shape and cross-sectional area of the oropharynx observed in people with chronic whiplash-associated disorders.49 These changes could be associated with such reported symptoms as hoarseness, difficulty in swallowing, or voice changes.
The neck muscles also lose strength and become more fatigable in the presence of neck pain.50 Electromyographic studies have also revealed greater fatigability in axioscapular muscles (upper trapezius).51 Notably the neck muscles lose their endurance capacity not only at maximum contractions but at lower contraction intensities,52 which have greater relevance to functional activities.
In tandem with changes in muscle behavior, biopsies have revealed changes in muscle fiber type in the neck flexors and extensors.53 Irrespective of the cause of neck pain (including whiplash-induced disorders), the cervical muscles sayed an increased proportion of type IIC transitional fibers, consistent with a transformation of slow-twitch oxidative type I fibers to fast-twitch glycolytic type IIB fibers. Functionally, this is consistent with the loss of muscles′ endurance capacity particularly at lower contraction intensities. Muscle atrophy has also been documented54–56 as well as widespread fatty infiltrate in both the flexor and extensor muscles of individuals with chronic whiplash-associated disorders.57,58 The highest fat indices were measured dorsally, in the deep rectus capitis minor and major and multifidi, and ventrally, in the deep longus capitis and colli; muscles with important roles in sensorimotor control. Initial evidence suggests that fatty infiltrate is a feature of chronic whiplash but not of chronic, insidious onset neck pain,59,60 which suggests there might be differences in pathophysiological mechanisms in transition to chronicity between these two neck pain groups.
IMPLICATIONS FOR CONSTRUCTING AN EXERCISE PROGRAM
A range of changes in muscle behaviors and properties as well as cervical movement have been identified in association with a whiplash injury and neck pain. These changes develop early after injury17,61,62 and persist into the chronic state in persons who have not recovered. Clinical trials have shown that various exercise interventions addressing one or other of the cervical movement or muscle function impairments can lessen pain.63–66 However, it has been shown that after both spinal and extremity joint injuries, pain relief does not necessarily infer that normal muscle function or range of movement has returned.17,67 Thus if aims are toward prevention of transition to chronicity or prevention of recurrent episodes of neck pain, it could be argued that exercise programs should address all presenting altered muscle behaviors and cervical movement deficits in attempts to restore optimal physical function.
For this purpose, a multielement exercise program that is introduced progressively is most likely required. Even though there is evidence of some cross-benefit of exercise types across different neuromuscular impairments,68 there is evidence that specificity in exercise prescription will better address individual impairments. For example, mobility exercises are necessary to improve range of movement and movement properties such as velocity and control deficits but such exercises do not improve, for example, the pattern of activation of the cervical flexors or their endurance capacity.33 In rehabilitation of the muscle system, it has been shown that changes in cervical motor control and posture are better rehabilitated with a low load motor relearning program than a strengthening regime.37,69 Conversely, strength and fatigability are not improved without the prescription of higher load exercise.70 Likewise disturbances in cervical kinesthetic sense are better addressed by a proprioceptive program of specific head relocation and eye–head coordination exercises71 than a muscle training exercise.68 Although a specific exercise for a specific impairment might seem intuitive, clinical trials to date have in the main tested one exercise approach63–66 which could suggest that all movement and neuromuscular impairments have not been rehabilitated.
Thus, it is proposed that an exercise program for physical rehabilitation needs to include exercises to address each movement or neuromuscular deficit, which is assessed to be present in a progressive manner. A trial of the effectiveness of such a progressive multielement exercise program for persons with chronic whiplash-associated disorders is currently in progress.72 Notably, whiplash-injured individuals are heterogeneous, not only in pain and disability levels, but in relation to the numbers and varieties of neuromuscular or sensorimotor disturbances. Not all patients have all impairments. Those reporting higher levels of pain and disability are more likely to present with a greater magnitude and variety of impairments.17,21,64,73 This emphasizes the importance of developing rehabilitation programs for specific individuals relevant to their individual presentation. Thus exercise programs will vary in their complexity from a relatively simple program for patients with lower pain levels and uncomplicated injuries to progressively more comprehensive programs for patients with high pain levels and potentially more complex disorders.
FACTORS TO CONSIDER IN IMPLEMENTING EXERCISE PROGRAMS
There is considerable controversy within the literature as to whether and when patients should receive active interventions for their whiplash-associated disorders.74–77 Further research is required to determine the optimal management approach in the acute stage of the disorder, as to date no one method of management appears to have changed the numbers of patients transitioning to chronicity.
In relation to implementing a physical rehabilitation program, due regard to pain and adequate pain management would appear to be most important factors. While a benefit of exercise can be a reduction in pain, the presence of moderate to severe pain may also impede rehabilitation of muscle function. As observed with experimental neck pain,44,78,79 pain induces immediate changes in muscle function and thus exercises which provoke pain stand to be counter productive. In addition, it has been shown experimentally that pain can impair the ability to learn a motor task.80 This was also clearly demonstrated in a clinical trial of management of patients with chronic whiplash-associated disorders.64 A change in the pattern of muscle activation in response to a motor relearning program was observed in many patients, but the training failed to improve muscle coordination in patients with higher levels of pain and disability in association with sensory signs indicative of the presence of augmented central pain processing. These latter patients overall showed little responsiveness to the physical rehabilitation program. This not only highlights the limitations of physical rehabilitation as a sole treatment approach for whiplash patients with complex pain syndromes, but points to the need for better understanding of the interactions and moderating effects of pain and associated psychophysical and psychological features on physical impairments and their rehabilitation. There is evidence, for example, that exercise in combination with training in pain coping skills was more effective than exercise alone in the management of chronic whiplash disorders.81 Further research is required into multidisciplinary management to determine the best way to proceed to achieve optimal physical and working capacity of the patient.
A further area requiring research is defining adequate dosage of exercise to achieve desired improvements in neuromuscular function. Any review of clinical trials reveals a considerable diversity in intervention periods,13 which clearly reveals that optimal dosage is unknown. This will be challenging research as, not unexpectedly, there is variability in the degree of impairment between individuals with neck pain,82 which would suggest that time for rehabilitation will be variable. A starting point could be multiple case–based physiological studies to investigate, for example, the relationship between exercise intensity and change in cervical muscle spatial and temporal relationships taking into account baseline dysfunction and pain. Equally important is addressing the multiple issues related to compliance or adherence with exercise in rehabilitation to obtain the desired outcomes.83
Physical rehabilitation is an integral component of the management of persons who have sustained a whiplash injury. Nevertheless further research is required to ensure the most beneficial exercise intervention is provided in the quest to lessen transition to chronicity or lessen recurrent episodes of neck pain. In addition, further research into effective multidisciplinary approaches to pain management is required to ensure an environment is created in which the effects of physical rehabilitation may be optimized.
- A whiplash injury results in reduced range and control of cervical motion and changes in neck muscles′ spatial and temporal relationships as well as strength and endurance.
- The presence or not and magnitude of impairments is highly variable between individuals.
- The effect sizes for current generic exercise programs are modest, suggesting that improvements can be made in exercise prescription.
- Research informs on the need for specificity in exercise prescription to progressively address presenting impairments and exercise programs need to be tailored to the individual.
- Further research is required to determine if specific, individualized exercise programs improves outcomes after a whiplash injury.
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