Static Muscle Contraction effect on Muscle Activity, Trapezius Blood Flow, and Autonomic Indices

(Warning! Long post!)
This article (see below) is of interest to me because of the monitoring of HRV (Heart rate variability, a measure of autonomic balance, or stress response) at rest and during different challenges such as cold stress test, static hand grip test, and deep breathing test. The author was kind enough to send me an unofficial copy of his/their study.
In the introduction it is pointed out that changes in muscle activity and muscle blood flow due to stress and unfavorable muscle loads are possible factors for initiation and maintenance of muscle pain through accumulation of metabolites, which stimulate nociceptive afferents. Sometimes impaired muscle circulation can accompany chronic neck pain. In previous studies fibromyalgia patients and subjects with trapezius myalgia were found to have restricted MBF (muscle blood flow) in response to acupuncture by needle stimulation in the trapezius muscle. This may be due to aberrations in the autonomic nervous system. Indeed, various studies have found evidence for ANS (autonomic nervous system) involvement in diffuse and widespread muscle pain, and fibromyalgia patients may have elevated sympathetic tone at rest. These aberrations can be exacerbated by mental stress. Less is known about localized muscle pain, such as addressed in this article.
So in a nutshell, this study found that subjects with muscle pain showed HRV results that indicated reduced basal parasympathetic activity. Their findings (which I won’t go into in detail here) indicated differences in intrinsic autonomic regulation, implying sympathetic-to-parasympathetic imbalance in chronic neck-shoulder pain. What has caused this imbalance is due to chronic pain, mental stress, or deconditioning is not known.
Their conclusion was that their findings support the hypothesis of ANS involvement at systemic and local levels in individuals with chronic neck-shoulder pain.
I bring this study to your attention for a few reasons.
1. It underscores what I tell first time patients with chronic pain from musculoskeletal problems: your pain may be worse after the first and even second acupuncture session because of an increase in blood flow that liberates many of the metabolites that can be “caught” in the vicious cycle of muscle tension and reduced blood flow.
2. It reinforces my belief in using points that have been studied and shown to decrease the stress response.
3. It reinforces my belief that autonomic balance remains a key component in pain management and in turn acupuncture treatment.
4. I was not aware of the blunted response of fibromyalgia patients to needling in the trapezius, so will have to amend and add means of increasing blood flow to the area during needling in these patients.

To read more about acupuncture, autonomic nervous system and my practice please click here.

Effects of static contraction and cold stimulation on cardiovascular autonomic indices, trapezius blood flow and muscle activity in chronic neck-shoulder pain

Department of Family Medicine and Public Health Sciences,
Division of Occupational and Environmental Health, Wayne
State University, 3800 Woodward Ave., Detroit, MI, USA
e-mail: bengt.arnetz@pubcare.uu.se
D. M. Hallman B. B. Arnetz
Department of Public Health and Caring Sciences,
Uppsala University, Uppsala, Sweden
123
Eur J Appl Physiol
DOI 10.1007/s00421-010-1813-z
Systemic cardiovascular characteristics
Subjects with muscle pain showed lower SDNN and LFHRV
during rest than the control group, indicating reduced
basal parasympathetic activity. However, there was no
increase in sympathetic activity as measured by LFnorm.
This is in line with recent studies that found diminishedHRV
in FM patients (Cohen et al. 2000) and in subjects with low
back pain (Kalezic et al. 2007). No significant difference was
found in IBI, in contrast with other studies on neck–shoulder
pain (Gockel et al. 1995; Sjo¨rs et al. 2009). In the present study, differences in autonomic reactivity
were indicated in response to HGT, but not in response to
CPT and DBT, namely the BP response to HGT was lower
in the pain group. These results are in accordance with the
blunted BP responses to exercise (Andersen et al. 2010;
Gockel et al. 1995) and normal BP responses to CPT
(Acero et al. 1999) demonstrated in previous studies
amongst subjects with neck–shoulder pain. Similar results
have been reported in patients with FM (Kadetoff and
Kosek 2010; Giske et al. 2008), indicating sympathic
hyporeactivity to various stressors (Martinez-Lavin 2007).
In the present study, however, only static contraction was
sensitive for differences in systemic BP, HRV and local
MBF, suggesting an altered exercise pressor reflex in the
pain group.
However, the increased LF reactivity observed in the
pain group during HGT should be interpreted with caution
as LF oscillations are influenced by both branches of the
ANS (Berntson et al. 1997). The current findings indicated
differences in intrinsic autonomic regulation, implying
sympathetic-to-parasympathetic imbalance in chronic
neck–shoulder pain. Whether this is a consequence of
chronic pain or due to other factors, e.g. mental stress or
deconditioning, requires further investigation. It is worth
noting, however, that although MVC was lower in the pain
Relations between symptoms and autonomic function
As expected, general health scores, as assessed with the
SF-36 questionnaire were lower in the pain group compared
to the healthy controls. More important, clinical
symptoms, e.g. dizziness and sweating, were more frequently
observed in the pain group. Using correlation
coefficients, a negative relationship was found between
disability of neck pain and resting LFnorm HRV and a
positive relation between disability and LFnorm reactivity
to static contraction. This is in line with previous findings
in low back pain (Gockel et al. 2008). Furthermore, an
inverse relationship between pain intensity and resting
SDNN was seen in the present study suggesting reduced
HRV with increased pain. Results show that it is worth to
plan treatment of neck–shoulder pain, aiming to restore
ANS balance at systemic and local levels.
myalgia had decreased vasodilatation capacity in these
muscles. Similarly, patients with generalised chronic
muscle pain, e.g. fibromyalgia (FM), had reduced MBF
following dynamic and during static exercise compared to
controls (Elvin et al. 2006). FM patients and subjects with
trapezius myalgia were found to have restricted MBF in
response to acupuncture by needle stimulation in the trapezius
muscle (Sandberg et al. 2005a).
A possible mechanism seems to be aberration in the
autonomic nervous system (ANS) (Maekawa et al. 2002;
Passatore and Roatta 2006). In chronic muscle pain, sympathetic
activity due to nociceptive stimulation may cause
disturbances of blood flow regulation in the affected
muscle and enhance muscle activation. This, in addition,
may be further exacerbated by mental stress (Larsson et al.
1995; Lundberg 2002).
Results from several studies provide evidence for ANS
involvement in diffuse and widespread muscle pain
(Martinez-Lavin 2007; Okifuji and Turk 2002). The autonomic
state in FM patients is characterised as elevated
sympathetic tone at rest, and hypo-reactivity to various
stressors, e.g. orthostatic stress, mental stress and isometric
exercise (Martinez-Lavin 2007; Giske et al. 2008). In
general, signs of ANS aberrations are reflected in heart rate
variability (HRV) and blood pressure (BP).
Although ANS may be involved in chronic muscle pain
of different origins, less is known about the degree of
autonomic involvement in localised chronic muscle pain,
especially pain in the neck–shoulder region (Leistad et al.
2008). Cardiovascular markers showed signs of sympathetic
dominance among persons with neck pain (Gockel
et al. 1995), low back pain (Gockel et al. 2008; Kalezic
et al. 2007), whiplash-associated disorders (Kalezic et al.
2010; Passatore and Roatta 2006) and distal forearm pain
among office workers (Gold et al. 2004; Sharma et al.
1997). Increased resting HR was found in subjects with
trapezius myalgia, whereas stress reactivity was unaltered
(Sjo¨rs et al. 2009).
To improve prevention and treatment, more knowledge
about ANS involvement in neck–shoulder pain is needed.
Tests are required which would differentiate between those
with and without muscle pain. Preferably, adequate assessment
should include multiple tests which target d