Unravelling the complexity of muscle impairment ... - Neck Pain Relief

Abstract
Manual Therapy 9 (2004) 125–133
Masterclass
Unravelling the complexity ofmuscle impairment in
chronic neck pain
D. Falla*
Division of Physiotherapy, The University of Queensland, Brisbane QLD 4072, Australia
Received 4 May 2004; accepted 8 May 2004
www.elsevier.com/locate/math
Exercise interventions are deemed essential for the effective management of patients with neck pain. However, there has been a
lack ofconsensus on optimal exercise prescription, which has resulted from a paucity ofstudies to quantify the precise nature of
muscle impairment, in people with neck pain. This masterclass will present recent research from our laboratory, which has utilized
surface electromyography to investigate cervical flexor muscle impairment in patients with chronic neck pain. This research has
identified deficits in the motor control ofthe deep and superficial cervical flexor muscles in people with chronic neck pain,
characterized by a delay in onset ofneck muscle contraction associated with movement ofthe upper limb. In addition, people with
neck pain demonstrate an altered pattern ofmuscle activation, which is characterized by reduced deep cervical flexor muscle activity
during a low load cognitive task and increased activity ofthe superficial cervical flexor muscles during both cognitive tasks and
functional activities. The results have demonstrated the complex, multifaceted nature of cervical muscle impairment, which exists in
people with a history ofneck pain. In turn, this has considerable implications for the rehabilitation ofmuscle function in people with
neck pain disorders.
r 2004 Elsevier Ltd. All rights reserved.
1. Introduction
Chronic neck pain is becoming increasingly prevalent
in society. Estimations indicate that 67% ofindividuals
will suffer neck pain at some stage throughout life (Cote
et al., 1998). With an increasing sedentary population,
especially with reliance on computer technology in the
workplace, it is predicted that the prevalence rate will
continue to rise. Effective management of this condition
is vital, not only for the relief of symptoms but perhaps
more importantly, for the prevention of recurrent
episodes ofcervical pain, personal su fering and lost
work productivity.
It is estimated that the osseoligamentous system
contributes 20% to the mechanical stability ofthe
cervical spine while 80% is provided by the surrounding
neck musculature (Panjabi et al., 1998). The ligaments’
role in stabilization occurs mainly at end ofrange
postures (Harms-Ringdahl et al., 1986) while muscles
*Corresponding author. Tel.: +61-7-3365-4529; fax: +61-7-3365-
2775.
E-mail address: d.falla@shrs.uq.edu.au (D. Falla).
1356-689X/$ - see front matter r 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.math.2004.05.003
ARTICLE IN PRESS
supply dynamic support in activities around the neutral
and mid-range postures, which are commonly adopted
during functional daily tasks. In the presence of injury
or pathology, the role ofthe muscular system becomes
even greater which highlights the need to address the
muscle system during both the assessment and rehabilitation
ofpatients with neck pain.
Exercise interventions are deemed essential for the
effective management of patients with neck pain. In the
past however, there has been a lack ofconsensus on
optimal exercise prescription. This results from a
paucity ofstudies to quantify the precise nature of
impairment in both the deep and superficial cervical
muscles in neck pain patients.
Anecdotal evidence (Janda, 1994) suggests the cervical
flexor muscles become dysfunctional in the presence of
neck pain. Furthermore, simple clinical mechanical
measures have demonstrated a reduction in the strength
and endurance capabilities ofthe cervical flexor muscles
in neck pain patients (Silverman et al., 1991; Vernon
et al., 1992; Watson and Trott, 1993; Barton and Hayes,
1996; Placzek et al., 1999). However, such basic
mechanical measures may oversimplify the deficits

126
within the muscle system in people with neck pain
disorders.
Detection, recording and analysis ofmyoelectric
signals with surface electromyography (EMG) provides
a more sophisticated means ofdetermining aberrant
muscle function. Although EMG has been used to
analyse superficial cervical muscle function in the past,
such investigations are infrequent and regular inconsistencies
in the applied methodology limits the interpretation
ofresults. Moreover, the inaccessibility ofthe
deep cervical flexor (DCF) muscles has rendered the use
ofconventional surface EMG measures inappropriate.
Recent research has refined the application ofsurface
EMG for the assessment of the cervical flexor muscles.
This has involved optimizing the application ofsurface
EMG for the assessment of the superficial cervical
flexors (sternocleidomastoid and the scalenes) (Falla
et al., 2002a, b) and secondly establishing a new EMG
electrode and technique for obtaining a direct measure
ofthe DCF muscles (Falla et al., 2003a).
Upon developing the methodology we investigated
cervical flexor muscle function in patients with neck pain
in three main areas ofEMG assessment (1) myoelectric
manifestations of cervical muscle fatigue (2) analysis of
the cervical flexor muscle activation patterns and (3)
analysis ofcervical neuromotor control. This paper will
(A)
Normalized values w.r.t. initial values
(B)
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60
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D. Falla / Manual Therapy 9 (2004) 125–133
Direction of
neck effort
Control
2 load cells,FS=250 N each
Normalized values w.r.t. initial values
present this recent evidence from our laboratory of the
complexity ofcervical muscle impairment in neck pain
patients and in turn will highlight the implications for
rehabilitation.
2. Muscle fatigability
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0 2 4 6 8
Time (s)
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0 2 4
Numerous studies have demonstrated a reduction in
the strength and endurance capacity ofthe cervical
flexor and extensor muscles in patients with neck pain
(Watson and Trott, 1993; Treleaven et al., 1994; Barton
and Hayes, 1996; Placzek et al., 1999). With advances in
EMG technology, more sophisticated measures have
been used to quantify cervical muscle fatigability in
patients with neck pain (Falla et al., 2003b, 2004e, f;
Gogia and Sabbahi, 1994). In a recent study (Falla et al.,
2003b) we examined fatigability of the sternocleidomastoid
(SCM) and anterior scalene (AS) muscles during
sustained cervical flexion contractions at 25% and 50%
ofthe maximum voluntary contraction (MVC) in
patients with chronic neck pain compared to controls.
Greater myoelectric manifestations of SCM and AS
muscle fatigue were identified for the neck pain patient
group as indicated by a significantly greater slope ofthe
mean frequency (Fig. 1). Whilst the results ofour study
Visual feedback display
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nMNF nARV nC V nFORCE
Neck Pain Patient
6 8 10 12 14
Time (s)
Fig. 1. (A) The subject’s head rests on a padded head support ofa custom designed cervical flexion force-measuring device. An adjustable Velcro
strap is fastened across the forehead acting to stabilize the head and provide resistance during cervical flexion isometric contractions. (B) Example of
fatigue plots obtained from the SCM muscle of a neck pain patient and control subject contracting at 50% of the MVC for the EMG variables
average rectified value (ARV), conduction velocity (CV), and mean frequency (MNF). The values of each variable are normalized with respect to the
intercept of the regression line. Greater fatigue of the SCM muscle is evident for the neck pain patient as characterized by the faster rate of change of
the MNF over time. (Adapted from Fig. 2 in Falla et al., 2003b).

confirmed greater fatigability of the cervical flexors at
moderate loads (50% MVC) which was identified by
Gogia and Sabbahi (1994), our results also established
greater cervical flexor muscle fatigability during low
load sustained contractions (25% MVC) in the patient
group which reflects the clinical observation ofreduced
endurance in the cervical flexors in neck pain patients
(Treleaven et al., 1994; Watson and Trott, 1993; Barton
and Hayes, 1996; Placzek et al., 1999). Furthermore, an
increase ofthe mean frequency at the beginning ofthe
contraction was observed for both muscles in the neck
pain group. This could be attributed to modification of
the recruited motor unit pool in which the number of
type II fibres is increased with respect to the type I fibres.
These findings were in accordance with results ofmuscle
biopsy studies ofsubjects with neck pain undergoing
spinal surgery, which established an increase in the
number oftype-IIC transitional fibres in the neck flexor
muscles resulting from transformations of slow-twitch
oxidative type-I fibres to fast-twitch glycolytic type-IIB
fibres (Uhlig et al., 1995).
Subsequent to these results, the specificity ofthis
aberrant muscle function was analysed (Falla et al.,
2004e). In examining for differences in the fatigability of
SCM and AS muscles between the painful and nonpainful
sides in patients with chronic unilateral neck
pain, results revealed greater estimates ofthe initial
value and slope of the mean frequency for both the SCM
and AS muscles ipsilateral to the side ofpain at 25%
and 50% ofMVC. These results indicate the need to
address fatigability of the cervical flexor muscles when
prescribing therapeutic exercise for neck pain patients.
The outcomes advocate the need for specificity and
perhaps a unilateral bias to therapeutic exercise in the
management ofpatients with unilateral neck pain to
attain optimal muscle rehabilitation. Ofinterest, the
duration ofneck pain does not appear to correlate with
the extent ofSCM and AS muscle fatigability in patients
with chronic neck pain. This finding would suggest that
the greater fatigability of the cervical flexor muscles,
which has been identified in patients with neck pain,
occurs early with the onset ofneck pain and does not
worsen with time (Falla et al., 2004f).
3. Muscle activation patterns during cognitive tasks
Whilst direct evidence ofdeep cervical extensor
muscle dysfunction has been identified in neck pain
patients (Hallgren et al., 1994; McPartland et al., 1997),
until recently, there was no succinct evidence that
described impairment in the DCF muscles. The DCF
muscles, including the longus colli, longus capitis, rectus
capitis anterior and rectus capitis lateralis, are histologically
and morphologically designed to provide support
to the cervical lordosis and the cervical joints (Winters
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D. Falla / Manual Therapy 9 (2004) 125–133 127
and Peles, 1990; Mayoux-Benhamou et al., 1994; Conley
et al., 1995; Vasavada et al., 1998; Boyd Clark et al.,
2001, 2002). Accordingly, our research has been
orientated towards the identification and quantification
ofdeficits in the DCF muscles in patients with neck pain
disorders.
Our interest commenced with the development ofthe
cranio-cervical flexion (C-CF) test (Jull et al., 1999; Jull,
2000), which is a low load task, based on the anatomical
action ofthe deep longus capitis and colli muscles. The
C-CF test was considered to provide an indirect measure
ofDCF muscle activation and endurance capacity,
which could be utilized in a clinical environment. The
test is performed in crook lying, and requires the person
to perform a head nod action (cranio-cervical flexion) in
five incremental stages ofincreasing range and hold each
position for 5–10 s. Performance is guided by feedback
from a pressure sensor, which is positioned suboccipitally
to monitor the flattening ofthe cervical
lordosis, which occurs with the contraction oflongus
colli (Mayoux-Benhamou et al., 1994, 1997).
Earlier clinical research demonstrated significantly
inferior performance on the C-CF test in patients with
idiopathic neck pain and with neck pain after a whiplash
injury (Jull et al., 1999; Jull, 2000). In general, patients
demonstrated a reduced ability to reach and maintain
the targets ofpressure in the cu funder the cervical
spine. Furthermore, surface EMG recordings of the
superficial cervical flexor (sternocleidomastoid) indicated
that performance on the test was associated with
significantly higher EMG amplitude ofthis muscle
compared with controls (Jull, 2000; Jull et al., 2004b).
Based on this research it was hypothesized that impaired
performance on the C-CF test (1) reflected a deficit in
motor control ofC-CF in patients with neck pain (2)
reflected poor activation ofDCF muscles and (3)
reflected poor muscle support ofcervical joints (Jull,
2000). The difficulty in substantiating these hypotheses
was related to the difficulty in obtaining a direct
recording ofthe DCF muscles due to their depth and
close proximity to nearby structures such as the
lymphatic system, the sympathetic chain, vagus nerve
and the carotid artery. However, our recent research
(Falla et al., 2003a) led to the development ofan
electrode capable ofrecording DCF muscle activity
(Fig. 2) without the need for fine wire EMG and thus
provided the opportunity to corroborate or refute these
hypotheses.
Utilizing this new EMG technique, we investigated
activation ofthe DCF muscles in patients with and
without chronic neck pain during performance of the C-
CF test (Falla et al., 2004c). The results demonstrated
reduced activation ofthe DCF muscles for the neck pain
patient group across all stages ofthe C-CF test with the
difference becoming statistically significant at the higher
levels ofthe test (representing increasingly inner range

128
positions ofC-CF (Fig. 3). Furthermore, the neck pain
patient group demonstrated reduced C-CF range of
motion across all stages ofthe C-CF test (Fig. 3). This
finding suggests that the pressure increase in the cuff
Connection to
suction tubing
(A)
Nasopharynx
(B)
Dens
Oropharynx
1c m
Electrode
contacts
Suction
portal
Nasal septum
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Nasopharyngeal Electrode
Uvula
Deep Cervical Flexors
Tongue
Fig. 2. (A) Electrode for the detection of DCF muscle activity. (B) A
nasopharyngeal application is used to suction surface electrodes over
the posterior oropharyngeal wall. The DCF muscles lie directly
posterior to the oropharyngeal wall, allowing myoelectric signals to be
detected from these muscles (adapted from Figs. 1 and 2 in Falla et al.,
2003a).
(A)
DCF normalised RMS values
(B)
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Cranio-cervical
flexion
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D. Falla / Manual Therapy 9 (2004) 125–133
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Visual feedback display
Pressure Biofeedback Unit
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% Full C-CF ROM
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0
under the cervical spine ofneck pain patients was
induced by a different movement strategy such as head/
neck retraction, which is commonly observed clinically.
Based on the results ofthis study it was concluded that
neck pain patients have a disturbance in the neck flexor
synergy, where impairment in the deep muscles,
important for segmental control and support, appears
to be compensated for by increased activity in the
superficial muscles (SCM and AS).
4. Neuromuscular efficiency
Increased EMG activity ofthe superficial cervical
musculature which has been identified in people with
neck pain during performance of the C-CF test (Jull,
2000; Jull et al., 2004b), could be considered an
inefficient neuromuscular activation pattern. This
concept was explored recently by investigating the
neuromuscular efficiency (NME) of the SCM and AS
muscles, defined as the quotient offorce and the
integrated EMG (van der Hoeven et al., 1993), during
cervical flexion contractions at 25% and 50% ofMVC
in patients with and without chronic neck pain (Falla
et al., 2004b). The results ofour study confirmed
less NME for the SCM and AS muscles contracting
at 25% MVC in the neck pain patient group. Reduced
NME indicates that the neck pain patients required
*
*
22 24 26 28 30
Stage of C-CFT (mmHg)
*
*
*
Control subjects
Neck pain patients
Fig. 3. (A) Subjects were positioned supine with the Pressure Biofeedback Unit placed sub-occipitally behind the neck to detect increases in pressure
with the gentle nodding action ofC-CF. Subjects received visual feedback ofpressure level. (B) Normalized root mean square (RMS) values (mean
and standard deviation) for the DCF muscles and percentage of full C-CF range of motion (ROM) for each stage of the C-CF test (C-CFT).
Indicates significant difference between control subjects and neck pain patients (Po0:05) (adapted from Figs. 1 and 2 in Falla et al., 2004c).

greater muscular electrical activity to produce an
equivalent amount offorce as compared to the control
subjects, or conversely, with a comparable amount of
electrical activity, neck pain patients would produce a
lower force output (Falla et al., 2004b). The greater
SCM and AS EMG activity recorded for the neck pain
group could theoretically be attributed to (1) greater
excitability ofthe motoneuronal pool, (2) modification
ofneural activation patterns accommodating for weakness
or inhibition ofanother muscle, or (3) a combination
ofthese mechanisms.
5. Muscle activation during functional tasks
Until now, the evidence ofcervical muscle impairment
presented within this manuscript corresponds to altered
muscle function identified during prescribed motor
tasks. In particular, research has demonstrated the
presence ofoveractivity or neuromuscular inefficiency
ofthe superficial cervical muscles under conditions of
low biomechanical load (Jull, 2000; Falla et al., 2004b,
c). However, this altered pattern ofneuromuscular
activation has been detected during non-functional
tasks. Therefore, extrapolation of these findings to
function must be done so with caution.
1.0
0.8
0.6
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10s
*
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Left SCM
Left AS
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Condition
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D. Falla / Manual Therapy 9 (2004) 125–133 129
*
* *
*
* *
* * *
* * * * *
post
Control Idiopathic WAD
In order to assess whether the presence ofincreased
EMG activity ofthe superficial cervical flexor muscles
was present during functional activities in people with
neck pain, we investigated activity ofthe SCM and AS
muscles during a low load, functional upper limb task
(Falla et al., 2004a). Subjects were asked to perform a
repetitive unilateral task, which involved marking three
targets, positioned on a desk in front of them, using
their right hand. Their left forearm rested motionless on
the desk in front of them. Previous research using this
task has demonstrated higher co-activation ofthe upper
trapezius muscle in neck pain patients compared to
controls during performance of the task and a decreased
ability to relax the upper trapezius muscle on completion
ofthe task (Nederhand et al., 2000).
As demonstrated in Fig. 4, the altered pattern of
muscle activation identified for both idiopathic neck
pain and whiplash patients was characterized by
increased EMG amplitude for the AS and SCM muscles
bilaterally throughout performance of the functional
activity. Furthermore, neck pain patients demonstrated
a decreased ability to relax the SCM and AS muscles on
completion ofthe task. It was suggested that the altered
pattern ofmuscle activation identified for the neck
pain groups represents an altered motor strategy to
minimize activation ofpainful muscles or compensate
1.0
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0.4
0.2
1.0
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0.4
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10s
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60s
Right SCM
*
*
Right AS
Condition
Fig. 4. Boxplots representing (25th quartile, mean, 75th quartile and 95% confidence intervals) normalized root mean square (RMS) values for the
left (L) and right (R) SCM and AS muscles in patients with whiplash associated disorder (WAD), idiopathic neck pain and control subjects. Values
are given for conditions 10, 60 and 120 s into the performance of a repetitive upper limb task and 10 s after completion of the repetitive upper limb
task (post). Indicate significant differences between groups calculated from the logarithm values of the data set. Statistical significance was defined
as the mean value for one group falling outside the 95% confidence interval of the comparison group. (Adapted from Fig. 1 in Falla et al., 2004a).
*
* *
*
*
120s
*
*
*
*
post

130
Relative latencies (ms)
Deltoid
onset
Relative latencies (ms)
Deltoid
onset
for inhibited muscles and might represent a functional
correlate ofperformance on the C-CF test (Falla et al.,
2004a).
6. Muscle activation during postural perturbations
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Flexion
DCF (R) SCM (L) SCM (R) AS (L) AS
Evidence was starting to reveal specific deficits within
the cervical flexor muscles in patients with neck pain.
This was identified during performance of prescribed
motor tasks and during functional activities. The next
stage ofour research was to identify whether the
automatic function of the cervical muscles was impaired
in people with neck pain.
We know from research in healthy individuals that
during performance of rapid arm movements which
induce a postural perturbation, the cervical muscles are
co-activated within 50 ms ofthe onset ofdeltoid activity.
This indicates that this response is too fast to be
mediated by even the fastest reflexes. Instead these
responses are considered to be preplanned by the
nervous system and are termed ‘‘feed-forward’’ adjustments
(Gurfinkel et al., 1988; van der Fits et al., 1998;
Falla et al., 2004g).
In reference to the lumbar spine model, a significant
delay has been identified for the transversus abdominis
muscle in patients with low back pain during rapid arm
movements (Hodges and Richardson, 1996). Utilizing
the same experimental model we aimed to determine
whether a deficit in the timing ofthe cervical muscles
would be present in people with chronic neck pain. The
results ofour study confirmed the hypothesis ofdelayed
onset ofthe DCF and the SCM and AS muscles in
*
DCF
Extension
(R) SCM (L) SCM (R) AS (L) AS
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D. Falla / Manual Therapy 9 (2004) 125–133
* *
* *
(A) (B)
AD EMG
DCF EMG
(L) AS EMG
(R) AS EMG
(L) SCM EMG
(R) SCM EMG
Control Neck Pain
Fig. 5. (A) Group data for neck flexor muscle EMG onsets during unilateral arm movements. Data are shown for the control (white bars) and neck
pain subjects (black bars). Mean and standard error of the relative latencies (ms) for the left (L) and right (R) SCM, AS and DCF muscles during
unilateral upper limb flexion and extension. Indicates significant difference Po0:05: (B) Representative electromyographic activity with rapid arm
movements. Raw EMG data are shown for the anterior deltoid (AD), DCF, SCM and the AS muscles for a control and chronic neck pain subject
during rapid upper limb flexion. Note the delayed activation of the neck muscles for the neck pain patient. (Adapted from Figs. 1 and 2 in Falla et al.,
2004d).
people with a history ofneck pain compared to control
subjects (Fig. 5) (Falla et al., 2004d).
Although each ofthe neck muscles demonstrated
some difference in onset time between groups, the DCF
demonstrated the most significant deviation during
rapid shoulder flexion. The relative latency ofthe
DCF contraction exceeded the criteria for feed-forward
contraction during movements in both directions in the
neck pain group, which indicates a significant deficit in
the automatic feed-forward control of the cervical spine.
Considering the deep cervical muscles, longus colli and
longus capitis, are fundamentally important for the
provision ofsupport for the cervical lordosis and the
cervical joints (Mayoux-Benhamou et al., 1994; Conley
et al., 1995; Vasavada et al., 1998), it was concluded that
a change in the feed-forward response might leave the
cervical spine vulnerable to strain (Falla et al., 2004d).
7. Implications for rehabilitation
100 ms
In summary, contemporary research has demonstrated
impairment in the deep cervical muscles, which
are considered to be functionally important for joint
support and control (Jull, 2000; Falla et al., 2004c, d),
deficits in muscle co-ordination which could result in
poor support and potential overload on cervical
structures (Jull, 2000; Falla et al., 2004a), insufficiency
in the pre-programmed activation ofcervical muscles
(Falla et al., 2004d), inefficient neuromuscular activation
(Falla et al., 2004b), and greater fatigability of
superficial cervical muscles in people with chronic neck
pain (Gogia and Sabbahi, 1994; Falla et al., 2003b,

2004e). In consideration ofthe evidence, it would seem
apparent that there is a need for specificity when
prescribing therapeutic exercise in the management of
people with neck pain.
There is some evidence to indicate that deficits in the
motor system occur early in the history ofonset ofneck
pain (Sterling et al., 2003) and does not resolve
automatically with lessening or resolution ofsymptoms
(Jull et al., 2002; Sterling et al., 2003). This would
suggest that therapeutic exercise forms an essential
component ofthe rehabilitation ofpatients with neck
pain, as a reduction ofpain alone would seem
insufficient to fully restore muscle function. Moreover,
it emphasizes the importance ofearly rehabilitation of
muscle function in people with neck pain disorders.
When developing exercises for treatment, it is
necessary to have an understanding ofabnormalities in
the muscular system associated with painful dysfunctional
joints. The results ofrecent research have
significantly advanced our understanding ofthe impairment
in the deep and superficial cervical flexor muscles
in patients with neck pain syndromes. This knowledge
provides the foundation to further develop and evaluate
specific exercises for the management of this condition.
Based on the muscle deficits considered to occur in
neck pain, two types ofexercise programs have been
proposed in the literature to address cervical flexor
muscle impairment. These two types ofexercise programs
are focused on two different functional requirements.
The first exercise regime consists ofgeneral
strengthening and endurance exercises for the neck
flexor muscles (Berg et al., 1994; Highland et al., 1992;
Jordan et al., 1998; Bronfort et al., 2001). These
exercises involve high load training and thus recruit all
the muscle synergists that is, both the deep and
superficial muscles. For example, strengthening the neck
flexor muscles is achieved by performing a head lift
manoeuvre which would recruit all muscles capable of
contributing to this action including, SCM, AS, longus
colli and longus capitis. A typical exercise program
would train the cervical flexors with the controlled head
lift exercise and focus on training endurance and
increasing the number ofrepetitions. Although several
studies have reported a reduction in pain and improvement
in function with this style of exercise (Highland
et al., 1992; Berg et al., 1994; Bronfort et al., 2001),
critical reviews and meta-analyses have generally concluded
that further well-designed randomized controlled
trials are warranted (Aker et al., 1996; Kjellman et al.,
1999; Panel, 2001).
The second exercise regime has been designed to focus
on the muscle control aspects and aims at improving
control ofthe muscles within the neck flexor synergy
(Jull et al., 2004a). In contrast to more traditional high
load strength and endurance exercises, low load exercise
is used to train the coordination between the layers of
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D. Falla / Manual Therapy 9 (2004) 125–133 131
neck flexor muscles. With this protocol, patients perform
and hold progressively inner ranges of C-CF while
trying to minimize activation ofthe superficial flexors.
This exercise approach is based on biomechanical
evidence ofthe functional interplay ofthe deep and
superficial neck muscles and on physiological and
clinical evidence ofimpairments in these muscles in
neck pain patients. The efficacy of this emphasis on retraining
the C-CF action in association with similar
exercises for the shoulder girdle was tested recently in a
randomized controlled clinical trial ofphysiotherapy
management for cervicogenic headache (Jull et al.,
2002). The results indicated that the specific exercise
program significantly reduced the frequency of headache
and neck pain and results were maintained in the long
term at the 12-month follow-up. General strengthening
exercises are not recommended in the early stages in this
exercise approach as it is considered that general
exercise will not necessarily address the dysfunction
between the deep and superficial muscles (Jull, 2000).
Thus specific emphasis is first placed on reeducating the
deep and postural muscles and general strengthening
exercises are only introduced once the imbalance
between the deep and superficial neck synergists has
been addressed.
However, the results ofrecent research have created
an interesting situation. There is evidence ofreduced
activation capacity ofthe DCF muscles with concurrent
increased activity in the superficial muscles. Conversely,
the superficial muscles have demonstrated greater
fatigability and there is evidence of less strength.
Therefore, there is some indication that both exercise
regimes may be beneficial in the management ofcervical
muscle dysfunction in neck pain patients.
Although clinical trials ofboth exercise regimes have
produced results to suggest a decrease in neck pain, the
physiological mechanisms ofefficacy ofcervical flexor
muscle retraining regimes remain uncertain. For example,
an improvement in DCF muscle activation would be
expected following an exercise program based on
retraining the activation capacity ofthe deep muscles.
However, would this program influence the fatigability
or neuromuscular efficiency of the superficial cervical
flexor muscles? Similarly, we would expect a training
regime focused on high load resistance training to
enhance superficial cervical flexor muscle strength and
reduce fatigability, but would it alter the neuromotor
control ofthe DCF muscles? There is a paucity ofgood
clinical studies regarding the efficacy of therapeutic
exercise in neck pain patients, precluding any consensus
on the most effective exercise prescribed. Although both
exercise regimes are based on sound theoretical rationale,
the mechanism of efficacy for either program is
unclear. Further research is warranted to evaluate the
physiological factors that change with each exercise
intervention and to compare the different exercise

132
modalities in order to identify the most effective means
to induce these changes. This work is currently underway.
8. Conclusion
In recent years, research has started to unravel the
complexity ofmuscle impairment, which occurs in
people with neck pain disorders. These findings have
considerable implications for the prescription of therapeutic
exercise. Whilst knowledge ofthe pathophysiology
underlying cervical muscle dysfunction remains
somewhat imprecise, the results ofrecent research have
contributed greatly to our understanding ofthe impairment
in the cervical muscles in people with neck pain,
which has lead to an improved understanding and
direction for the management of this condition. Further
research is now necessary to clarify the physiological
mechanisms ofefficacy ofcervical muscle retraining to
ensure evidence based, optimal practice is embraced in
modern practice.
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