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R E S E A R C H Open Access
Effect of lumbar spinal manipulation on
local and remote pressure pain threshold
and pinprick sensitivity in asymptomatic
individuals: a randomised trial
Sasha L. Dorron
1*
, Barrett E. Losco
1
, Peter D. Drummond
2
and Bruce F. Walker
1
Abstract
Background: The mechanisms of clinical pain relief associated with spinal manipulative therapy (SMT) are poorly
understood. Our objective was to determine whether lumbar high-velocity low-amplitude SMT altered pressure
pain threshold (PPT) and pinprick sensitivity (PPS) locally and remotely, how long any change lasted (up to 30 min),
and whether changes related to the side of SMT.
Methods: Thirty-four asymptomatic participants (mean age 22.6 years ±4.0) received a right- or left-sided lumbar
SMT. PPT and PPS were measured bilaterally at the calf, lumbar spine, scapula, and forehead before and
immediately, 10, 20, and 30 min after intervention. Data were collected between October 2014 and June 2015.
Results: Bilateral calf and lumbar spine PPT increased significantly after 10 –20 min and was maintained at 30 min
(7.2–11.8 % increase). PPS decreased significantly in all locations at various times (9.8 –22.5 % decrease). At the calf
and lumbar spine, PPT increased slightly more ipsilateral to the SMT than contralateral.
Conclusions: Lumbar SMT reduced deep pressure sensitivity locally and in the lower limbs for at least 30 min,
whereas sensitivity to pinprick was reduced systemically. These findings suggest that SMT specifically inhibits deep
pressure sensitivity distally. These findings are novel compared to other lumbar SMT studies, and may reflect a local
spinal or complex supraspinal analgesic mechanism.
Trial registration: Registered with the Australian New Zealand Clinical Trials Registry (ACTRN12614000682640).
Keywords: Spinal manipulative therapy, Lumbar spine, Pain sensitivity, Pressure pain threshold, Pinprick sensitivity
Background
Spinal manipulative therapy (SMT) is a manual therapy
technique used by various health care professions
including chiropractors, osteopaths and physiotherapists
[1]. Evidence is mixed but some studies suggest that
SMT may be effective in managing non-specific spinal
pain and some types of headache [2–7]. Since musculo-
skeletal conditions, particularly low back pain (LBP),
represent a significant economic burden and affect a
substantial proportion of the population [8, 9], improv-
ing our management of these conditions is important.
There is a lack of evidence to explain how SMT may
achieve positive clinical outcomes such as pain relief.
Improving our understanding of the neurophysiological
effects of SMT may improve its clinical use and allow
practitioners to make better choices about when and
where to apply SMT.
Pressure pain threshold (PPT) is a widely used form of
experimental pain, which represents the amount of
mechanical pressure required to elicit a nociceptive
response at the testing site. It is thought deep Aδand C
sensory fibres are activated at the PPT [10–12].
Pinprick sensitivity (PPS), on the other hand, is not
widely used in manual therapy research, and is measured
by the self-reported pain response to a sharp stimulus to
* Correspondence: s.dorron@murdoch.edu.au
1
Discipline of Chiropractic, School of Health Professions, Murdoch University,
90 South Street, Murdoch, WA 6155, Australia
Full list of author information is available at the end of the article
© 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Dorron et al. Chiropractic & Manual Therapies (2016) 24:47
DOI 10.1186/s12998-016-0128-5
the skin. PPS is a superficial nociceptive response
mediated by Aδfibres [10, 12].
The short-term effect of SMT on various forms of
experimental pain has been studied previously, but many
gaps remain. Two recent systematic reviews concluded
that SMT has an overall effect of increasing PPT (redu-
cing sensitivity) at sites local to the SMT and remotely
[13, 14]. The remote effect may be regional [15, 16] (at a
peripheral site innervated by the target spinal region) or
systemic [17–20]. SMT also appears to reduce sensitivity
to other types of experimental pain [13, 14]. Curiously,
PPT increases after cervical SMT but this change has
not been shown after lumbar SMT [21–26]. The reason
for this is unknown and seems biologically questionable.
It could reflect widely differing methods that may have
affected the outcomes. The effect of SMT on PPS is
unknown. The literature on this topic was considered
sufficiently weak to justify further investigation.
ThedurationofchangetopainsensitivityfollowingSMT
is also unknown as, in the few studies that have collected
data beyond 10 min, findings are mixed [15, 16, 27, 28].
Reductions in pain sensitivity appear to be bilateral
[29–33], but there may be asymmetry related to dominant
side [31, 32] or side of SMT [29, 30, 33].
Aims
This research aimed to investigate the effects of lumbar
SMT on PPT and PPS, locally and remotely, for 30 min
following SMT, and the effects of SMT on the unilateral
compared to contralateral side of the body. We were
interested in determining whether lumbar SMT had a
hypoalgesic effect that was selective to certain stimuli, or to
certain regions or sides of the body. Our additional aim was
to delineate the short-term time course of any change.
Methods
This study was a single-blind two-arm randomised trial,
and was approved by the Human Research Ethics
Committee of Murdoch University (permit 2014/141).
Participants
Asymptomatic participants aged 18–45 years were
recruited from the Murdoch University campus (Perth,
Western Australia), via in-class announcements and
flyers, and from the general public via word of mouth.
Participants were excluded if any of the following
applied: (a) current chronic pain condition anywhere, (b)
current acute or sub-acute LBP, (c) contraindication to
lumbar SMT, (d) qualified chiropractor or student in 4
th
or 5
th
year of chiropractic university degree (presumed
to be more likely to introduce expectancy bias due to
prior knowledge of the neurophysiology of SMT), (e)
taken pain-relieving medication in the preceding 24 h,
(f) had alcohol within the preceding 12 h.
Originally, an inclusion criterion of naivety to spinal
manipulation was included. However, significant diffi-
culty with recruitment led us to remove this and instead
add exclusion criterion (d), above.
Outcome measures
Pressure pain threshold
PPT, as a measure of deep mechanical pain sensitivity,
was measured using an algometer (FDIX, Wagner
Instruments, USA) with a 1 cm
2
rubber probe. The alg-
ometer was validated and standardised against a Kistler
Force Plate prior to use in this study (Pearson’s r = 0.99,
p= .01). For measurement, the algometer was placed
perpendicular to the skin and pressure was increased at
a rate of 500 g/cm
2
per second, monitored real-time on
the digital algometer display by the assessor. The partici-
pant was asked to say “Yes”when the sensation of pres-
sure first changed to pain, at which point the algometer
was removed and the maximum pressure recorded.
Single measurements at each site were taken following a
standard pattern, repeated three times to obtain three
measurements per site. This validated approach allowed
sufficient rest time between measures at each site [34, 35].
We used a cut-off point of 10 kg/cm
2
for the forehead and
scapula [36], and 12.5 kg/cm
2
for the lumbar and gastro-
cnemius sites as this was the upper limit of the algometer.
If the cut-off was reached, the cut-off value was used as
the measurement for that site and the algometer removed.
The average of the second and third measures was used
for analysis [36]. An increase in PPT represents a decrease
in sensitivity.
Pinprick sensitivity
PPS, as a measure of superficial pain sensitivity, was
measured using the Neuropen with Neurotips (Owen
Mumford, UK). This device is designed to consistently
exert 40 g of force when pressed into the skin, though
no reliability studies were found for its use. An 11-point
Numerical Rating Scale (NRS) was used where 0 = not
sharp, and 10 = extremely sharp, as used previously in an
experimental trial [37]. The device was placed perpen-
dicular to the skin and pressed in until the guiding
markers were aligned; this was maintained for one
second and then removed. The participant was then
asked to verbally report the intensity of the sharpness
using the NRS. Measurements were performed once at
each site, immediately following the completion of PPT
measures. A new tip was used for each participant. A
decrease in PPS represents a decrease in sensitivity.
Interventions
A high-velocity low-amplitude SMT was targeted at the
L5-S1 spinal segment. A commonly used SMT tech-
nique, referred to as the hypothenar mammillary push
Dorron et al. Chiropractic & Manual Therapies (2016) 24:47 Page 2 of 9
[38], was used (Fig. 1). The participant was placed in a
side-lying position, with the upper leg bent and the
lower leg straight. The researcher stabilised the partici-
pant at the shoulder with their cephalad hand, and at
the thigh with their own leg. A manual contact with the
researcher’s caudal hand was then taken over the L5
mamillary process on the right or left side (allocated
randomly), the joint was taken to pre-tension, and a
high-velocity low-amplitude thrust delivered targeting
the L5-S1 facet joint in a posterior to anterior direction.
If the clinician thought that the first SMT was ‘unsuc-
cessful’, he was allowed to perform a second SMT. The
absence of a facet joint cavitation (audible release)
during the SMT was not considered sufficient alone to
attempt a second SMT, as there is no evidence that a
cavitation is a necessary component of a ‘successful’
manipulation [39–41].
Procedure
Participants attended a single session at Murdoch
University campus, where they completed intake forms,
read an information letter, and completed informed
consent. Individual participants were given two practice
attempts for each outcome measure, applied to the hand,
to familiarise them with the procedure. The following
four locations were then marked bilaterally on the skin
with a non-permanent marker: (a) infraspinatus muscle
belly, 2 cm lateral and interior to the root of the spine of
the scapula, (b) 2 cm lateral to the L5 spinous process
over the paraspinal muscles, (c) mid-portion of the
medial gastrocnemius muscle belly, (d) frontal eminence
of the forehead. Baseline outcome measures were taken,
PPT being measured before PPS, and the assessor then
left the room to remain blind to which side SMT was
applied. The researcher performing the intervention, a
registered chiropractor with 15 year’s clinical and
academic experience, randomised participants into one
of two groups using the GraphPad random number
generator [42] to generate a 1:1 list of 1’s and 2’s, which
were placed into sequentially numbered, sealed, opaque
envelopes. The envelope was opened immediately prior
to the intervention based on order of enrolment into the
study. After the intervention was administered, the
assessor re-entered the room and measured outcomes
immediately, at 10, 20, and 30 min.
Power analysis
A power analysis using G*Power 3.1 software (University
of Düsseldorf, Germany) showed that a sample size of
34 would provide 80 % power for detecting a large effect
size of 0.4.
Data analysis
Data were analysed using SPSS Version 23. A repeated-
measures analysis of variance was conducted for PPT
and PPS at each location, using factors of time (baseline,
immediate, 10, 20, and 30 min), side (side of measure-
ment), and group (side of manipulation, where right
SMT = R-SMT and left SMT = L-SMT). Simple contrasts
between baseline and each subsequent time point were
included in the analyses. Further interactions were inves-
tigated using paired t-tests. Effect sizes are reported as
partial Eta squared (ƞ
P
2
), where ≥0.10, ≥0.25, and ≥0.50
are considered to represent small, moderate, and large
effect sizes respectively [43].
Results
Thirty-four participants (20 male) were recruited for
data collection and included in analysis (Fig. 2), with a
mean age of 22.6 years (±4.0, range 18–36). Data were
collected between October 2014 and June 2015, ending
when 34 participants with usable data completed the
trial. Baseline characteristics, including PPT and PPS
values, are reported in Table 1. No harms were reported
during or after follow-up. The intervention was consid-
ered successful in all cases at the first attempt; thus, no
participant received a second SMT.
Pressure pain threshold
Significant effects over time were observed for calf (p=.03,
ƞ
P
2
= .09) and lumbar spine PPT (p= .003, ƞ
P
2
= .15) with
weak effect sizes. Contrasts between baseline and subse-
quent time points revealed significant increases in PPT
from baseline to 20 and 30 min at the calf, and from
baseline to 10, 20 and 30 min at the lumbar spine (Table 2,
Fig. 3). There was no effect over time for PPT at the scapula
(p=.71,ƞ
P
2
=.01) or forehead (p=.67,ƞ
P
2
= .01).
Significant effects were observed for side at the calf
(p= .001, ƞ
P
2
= .32) and lumbar spine (p=.01, ƞ
P
2
=.21)
with moderate and weak effect sizes respectively. In par-
ticular, PPT was higher on the right compared to the left
at both the calf (5.4 kg/cm
2
and 4.8 kg/cm
2
respectively)
and lumbar spine (7.1 and 6.7 kg/cm
2
respectively). There
was no difference between sides at the scapula (p=.87,
ƞ
P
2
= .001) or forehead (p=.64, ƞ
P
2
=.01).
Fig. 1 Right L5-S1 SMT technique
Dorron et al. Chiropractic & Manual Therapies (2016) 24:47 Page 3 of 9
No significant differences were detected between
groups including across time and side for PPT at the
calf, lumbar spine, scapula or forehead.
Pinprick sensitivity
Significant effects over time were observed for PPS at the
calf (p=.01, ƞ
P
2
= .10), lumbar spine (p=.00, ƞ
P
2
=.21),
and forehead (p=.02, ƞ
P
2
= .10), each with weak effect
sizes, but not at the scapula (p=.13, ƞ
P
2
= .05). Contrasts
revealed significant decreases in PPS at the calf between
baseline and 20, and 30 min. At the lumbar spine, signifi-
cant decreases were noted between baseline and immedi-
ate, 10, 20, and 30 min. At the forehead, decreases were
noted between baseline and 10, 20, and 30 min. Despite
no over-all effect for Time at the scapula, contrasts re-
vealed significant decreases from baseline to 10 min, and
20 min (Table 3).
Significant effects were observed for side at the calf
(p= .049, ƞ
P
2
= .12) and forehead (p=.001, ƞ
P
2
=.29) with
weak and moderate effect sizes respectively. In detail, PPS
was found to be higher on the right compared to the left
at both the calf (4.5 and 4.3) and forehead (4.6 and 4.2).
There was no difference between sides at the lumbar spine
(p=.91,ƞ
P
2
= .00) and scapula (p=.63, ƞ
P
2
=.01).
A between-group difference was found at the scapula
(p= .04, ƞ
P
2
= .12) with a weak effect size. In detail, the
L-SMT group had higher overall scapula PPS compared
to the R-SMT group (4.2 and 2.9 respectively). A signifi-
cant side x group interaction at the scapula was also
found (p= .03, ƞ
P
2
= .14) with weak effect size. The data
indicate that in the R-SMT group, right scapula PPS was
lower than the left (2.8 and 3.1 respectively), but this
was reversed in the L-SMT group (4.4 and 4.0 respect-
ively). These likely reflect baseline differences between
groups.
Fig. 2 Data collection flow chart
Table 1 Baseline characteristics
R-SMT L-SMT Actual difference
(% difference)
Gender 8 female,
9 male
6 female,
11 male
-
Mean age, years 22.6 (3.1) 22.5 (4.8) 0.1 (0.3)
Dominant hand 11 right, 6 left 16 right, 1 left -
Calf PPT 5.1 (2.2) 4.5 (1.9) 0.6 (12.2)
Lumbar Spine PPT 7.1 (2.9) 5.9 (2.6) 1.2 (17.3)
Scapula PPT 5.1 (1.9) 4.1 (1.8) 0.9 (18.2)
Forehead PPT 2.8 (1.0) 2.4 (1.0) 0.5 (15.9)
Calf PPS 4.1 (2.2) 5.1 (2.4) 1.0 (19.5)
Lumbar Spine PPS 4.3 (1.6) 5.3 (2.1) 0.9 (17.9)
Scapula PPS 3.2 (1.7) 4.5 (2.0) 1.3 (28.5)
Forehead PPS 4.4 (1.8) 5.3 (2.4) 0.9 (17.3)
Abbreviations:R-SMT right spinal manipulative therapy group, L-SMT left spinal
manipulative therapy group, PPT pressure pain threshold, PPS
pinprick sensitivity
Note: where appropriate, data reported as mean (standard deviation), PPT
reported in kg/cm
2
, PPS on 11-point numerical rating scale
Dorron et al. Chiropractic & Manual Therapies (2016) 24:47 Page 4 of 9
No further significant differences were detected be-
tween groups, including across time and side, for PPS at
the calf, lumbar spine, scapula or forehead.
Ipsilateral vs. Contralateral changes
No significant time x side x group changes were
detected. However, t-tests between baseline and each
subsequent time point indicated that PPT increases were
slightly greater on the side ipsilateral to the SMT in the
calf particularly, and to a lesser extent in the lumbar
spine (see Additional file 1).
Discussion
This is the first study to observe significant increases in
PPT at the lumbar spine and calf following lumbar high-
velocity low-amplitude SMT, and to discover that these
changes appeared to develop over 10 –20 min and
persist to 30 min.
PPS, an unvalidated outcome measure, was seen to
decrease over time at all locations. This could be a
systemic real effect or may represent a non-specific
effect such as a learned response or adjustment to
repeated measurement. Both types of pain sensitivity are
mediated by Aδfibres, but PPT additionally involves C
fibres. Since changes in PPT were not systemic in the
present study, a systemic treatment effect on PPS is
considered unlikely. Further research may be warranted
to clarify this.
The magnitude of change in PPT was small, ranging
from 7.2 to 11.8 %. The minimum detectable change for
PPT has not been clearly defined, but is likely between
35 and 50 % [35, 44, 45]. Percentage change is likely to
be most relevant when considering PPT, as absolute
baseline values differ widely between testing sites [45].
Based on these minimum detectable change values, our
changes may be due to measurement error or chance.
The magnitude of changes (as percentage) observed in
the present study are similar to some [28] but smaller
than other studies [19, 46], but falls within the range
identified in the systematic review by Millan et al. [13]
of 4.8 to 44.2 %. In our study, as increases in PPT at the
calf and lumbar spine were gradual and consistent, and
absent at the scapula and forehead, we believe that
lumbar SMT evoked a real but small change in PPT.
We observed some asymmetry between the right and
left sides. The right calf and lumbar spine were less
sensitive overall than the left when measuring PPT, while
the right calf and forehead were more sensitive overall
than the left when measuring PPS. This is probably a
reflection of baseline differences. This finding is at odds
with the literature as others have noted no systematic
differences in PPT between sides of the body or depending
on hand dominance [34, 47, 48]. Our observations may
relate to methodological decisions (the left side was always
measured before the right), or another unknown factor.
Other literature investigating the effect of SMT on
PPT is conflicting. Five studies investigating the effect of
lumbar SMT on PPT have found no significant change
[21, 23–26]. Four of these measured PPT only immedi-
ately following SMT [21, 23–25], so it is possible they
may have missed an effect that developed over time, as
occurred in our study. The remaining study found a
trend toward increasing PPT but this did not reach sig-
nificance at 30 min [26]. Another study noted, unusually,
a significant decrease in PPT after 10 and 15 min [22].
This study did not have a comparison group, and since a
nerve conduction study was performed immediately
prior to PPT, PPT measures may have been confounded.
The results of studies in the lumbar spine are in stark
contrast to cervical spine literature, which quite consist-
ently demonstrate increases in PPT [16, 19, 28–31, 46, 49],
and are in agreement with our own study of the lumbar
spine. Additionally, other studies have demonstrated mech-
anical hypoalgesia following lumbar mobilisation [50, 51],
Table 2 Changes in pressure pain threshold over time
Mean PPT,
kg/cm
2
(SD)
Difference compared
to baseline, kg/cm
2
(% change)
p-value (effect
size), compared
to baseline
Calf
Baseline 4.8 (2.1) - -
Immediate 5.1 (2.2) 0.3 (5.4 %) .11 (.08)
10 min 5.1 (2.2) 0.4 (7.3 %) .05 (.11)
20 min 5.2 (2.2) 0.5 (9.6 %) .02* (.17)
30 min 5.2 (2.0) 0.4 (9.0 %) .03* (.14)
Lumbar spine
Baseline 6.5 (2.8) - -
Immediate 6.7 (2.7) 0.2 (3.7 %) .25 (.04)
10 min 7.0 (2.5) 0.5 (7.2 %) .03* (.13)
20 min 7.1 (2.7) 0.6 (9.2 %) .01* (.19)
30 min 7.3 (2.6) 0.8 (11.8 %) .01* (.21)
Scapula
Baseline 4.6 (1.9) - -
Immediate 4.6 (2.0) −0.01 (−0.2 %) .88 (.001)
10 min 4.7 (2.1) 0.1 (2.4 %) .45 (.02)
20 min 4.7 (1.9) 0.1 (2.6 %) .44 (.02)
30 min 4.7 (1.7) 0.1 (2.0 %) .58 (.01)
Forehead
Baseline 2.6 (1.0) - -
Immediate 2.7 (1.1) 0.1 (2.3 %) .40 (.02)
10 min 2.7 (1.1) 0.1 (2.3 %) .45 (.02)
20 min 2.7 (1.0) 0.1 (1.9 %) .58 (.01)
30 min 2.7 (1.0) 0.1 (3.1 %) .34 (.03)
Abbreviations:PPT pressure pain threshold, SD standard deviation, * = p≤.05.
Note: effect size reported as partial eta squared (ƞ
P
2
)
Dorron et al. Chiropractic & Manual Therapies (2016) 24:47 Page 5 of 9
lending further strength to our findings. The differences in
the literature may relate to methodological differences in
terms of PPT testing sites and study populations. Alterna-
tively, differences in mechanoreceptor and nociceptor
density, in baseline PPT values, or in the neurophysiologic
response to SMT between different spinal regions may
explain the inconsistency in the literature [22].
The duration of change in PPT after SMT is not well
studied. Cervical and thoracic spine studies have observed
increases in PPT at 10 min [19, 20], 15 min [15], 20 min
[28], and 30 min [27]. Others have seen no change at
10 min [52], and 2 h [16]. We demonstrated a small
change that persisted at 30 min.
Studies that have shown a systemic change over time
in PPT following SMT have all failed to show differences
when compared to other active treatments or a control
condition [17–20], calling into question whether a
specific systemic response to SMT occurs. This contrasts
with one sham-controlled study [15] and one study
comparing two types of SMT which show only local and
regional changes following SMT [16]. Our findings
suggest that deep mechanical hypoalgesia in response to
lumbar SMT is local and regional, but not systemic.
A recent systematic review found no correlation between
pain thresholds (including PPT) and subjective pain inten-
sity or disability [53]. PPS does not appear to have been
studied in this capacity. It is unknown whether change in
PPT following SMT relates to short- or long-term clinical
improvement, or if the response differs between healthy
and symptomatic populations. Hypothetically, it is possible
that a window of hypoalgesia following SMT could pro-
mote exercise and physical activity in spinal pain patients.
While changes in pain sensitivity following SMT may not
currently translate into clinical recommendations, it still
represents a promising avenue for experimental research
into the neurophysiologic effects of SMT.
Several neurophysiological theories to explain deep
mechanical hypoalgesia following SMT have been proposed.
Fig. 3 Changes in pressure pain threshold over time with standard error bars. Abbreviations: PPT = pressure pain threshold, Base = baseline,
Immed. = immediate, * = p ≤.05 compared to baseline
Dorron et al. Chiropractic & Manual Therapies (2016) 24:47 Page 6 of 9
These include activation of the descending inhibitory
pain control system or activation of the pain gate mechan-
ism [54]. The descending inhibitory pain control system is
able to selectively modulate C-fibre nociceptive signals
[55], which would be expected to affect PPT (mediated by
C- and Aδ-fibres) but not PPS (mediated only by Aδ-
fibres). This system is also capable of acting regionally in
the spinal cord [56], which could explain the local and
regional hypoalgesia we observed. An animal-model
experiment demonstrated that mechanical hypoalgesia
induced by joint manipulation was mediated by the neuro-
transmitters serotonin and noradrenaline, both of which
are involved in the descending inhibitory pain control
system [57]. Thus, activation of the descending inhibi-
tory pain control system may offer a plausible explan-
ation for our findings. The pain gate mechanism is
activated only when there is a concurrent non-nociceptive
stimulus [58] and thus would likely not account for the
more prolonged hypoalgesia we observed. Ultimately,
post-SMT hypoalgesia likely arises from a combination of
neurophysiologic mechanisms, as well as placebo and
psychosocial factors [59].
Strengths and limitations
There are several strengths to the present study. We
followed best practice conditions (based on CONSORT
guidelines), and used an a priori power calculation,
assessor blinding, participants who were unfamiliar with
the neurophysiology of SMT, a single experienced clin-
ician providing interventions, and a validated instrument
for measuring PPT.
There are also various limitations. Firstly, we acknow-
ledge that measuring PPS may have had a confounding
effect on PPT, though PPS was always measured after
PPT and followed by a rest period before the next
follow-up to minimise this possibility. PPS was also an
unvalidated and subjective measure, and participants’
individual criterion for sharpness intensity may have
changed with repeated measurement. Next, anxiety is a
known confounder to pain [60], which was not con-
trolled for other than with a thorough informed consent
process and assuring participants that SMT was unlikely
to cause pain. As our study recruited mainly young,
asymptomatic participants, the generalisability of the
results is limited when considering older or symptomatic
Table 3 Changes in pinprick sensitivity over time
Mean PPS, 11-point NRS (SD) Difference compared to baseline, 11-point NRS (% change) p-value (effect size), compared to baseline
Calf
Baseline 4.6 (2.3) - -
Immediate 4.6 (2.1) −0.02 (−0.4 %) .94 (.000)
10 min 4.5 (2.4) −0.1 (−3.2 %) .51 (.01)
20 min 4.1 (2.2) −0.5 (−11.5 %) .04* (.13)
30 min 4.0 (2.2) −0.6 (−13.6 %) .02* (.16)
Lumbar Spine
Baseline 4.8 (1.9) - -
Immediate 4.1 (2.1) −0.6 (−13.4 %) .003* (.24)
10 min 3.9 (2.3) −0.9 (−18.0 %) .001* (.30)
20 min 4.0 (2.0) −0.8 (−17.1 %) .001* (.29)
30 min 3.7 (2.2) −1.1 (−22.5 %) .000* (.42)
Scapula
Baseline 3.9 (1.9) - -
Immediate 3.6 (2.1) −0.3 (−6.7 %) .28 (.04)
10 min 3.4 (1.9) −0.5 (−12.4 %) .03* (.15)
20 min 3.5 (2.1) −0.4 (−9.8 %) .04* (.13)
30 min 3.5 (2.0) −0.3 (−8.8 %) .11 (.08)
Forehead
Baseline 4.8 (2.1) - -
Immediate 4.7 (2.2) −0.1 (−2.7 %) .45 (.02)
10 min 4.3 (2.0) −0.5 (−10.8 %) .04* (.13)
20 min 4.1 (2.0) −0.7 (−14.8 %) .007* (.20)
30 min 4.2 (2.3) −0.6 (−13.1 %) .05* (.12)
Abbreviations:PPS pinprick sensitivity, NRS numerical rating scale, SD standard deviation, * = p≤.05. Note: effect size reported as partial eta squared (ƞ
P
2
)
Dorron et al. Chiropractic & Manual Therapies (2016) 24:47 Page 7 of 9
populations. Additionally, we did not have a sham group
so some of the effects may be explained by placebo or
other non-specific effects such as the positioning or
physical touch, or a learned effect. However, it is difficult
to envision how such effects would be expressed as
regional hypoalgesia. Though participant blinding in
manual therapies is difficult [61], a non-thrust manual
contact group would have been valuable. Finally, though
the study was adequately powered to detect large main
effects, it was likely underpowered to detect small
changes and two-way and three-way interactions involv-
ing side of stimulation or asymmetry of response; thus,
we may have committed some type II errors.
Conclusions
As the only study to date to have demonstrated short-
term deep mechanical hypoalgesia following lumbar
high-velocity low-amplitude SMT, replication of our
results is required before firm conclusions can be drawn.
Future research should be directed at measuring mech-
anical hypoalgesia for at least 30 min following SMT,
and comparing the effects of SMT in different spinal re-
gions on pain sensitivity to determine if there are indeed
differences between regions. Additionally, furthering our
understanding of the neurophysiological pathways that
may be involved is important.
Additional file
Additional file 1: Ipsilateral vs. Contralateral Changes in Pressure Pain
Threshold and Pinprick Sensitivity. Description of data: Data tables and
figures showing comparisons of change in PPT and PPS on ipsilateral and
contralateral sides to SMT. (DOCX 81 kb)
Abbreviations
LBP: Low back pain; L-SMT: Left-sided spinal manipulative therapy;
NRS: Numerical rating scale; PPS: Pinprick sensitivity; PPT: Pressure pain
threshold; R-SMT: Right-sided spinal manipulative therapy; SMT: Spinal
manipulative therapy
Acknowledgements
Not applicable.
Funding
This study was funded by an intra-mural grant from the School of Health
Professions, Murdoch University, Western Australia. The funding body had no
role in the study design, data collection, analysis or interpretation of the data.
Availability of data and materials
The datasets analysed during the current study are available from the
corresponding author on reasonable request.
Authors’contributions
All authors contributed to the design of the study. SD and BL conducted the
data collection. SD performed the statistical analysis with assistance from PD.
SD wrote the first manuscript draft and performed revisions with input from
all authors. All authors agreed to the final manuscript.
Competing interests
Bruce F Walker is Editor in Chief of Chiropractic & Manual Therapies but played
no part in the editorial process of this submission. All other authors declare that
they have no competing interests.
Consent for publication
Consent for publication has been obtained for any relevant images in this
manuscript.
Ethics approval and consent to participate
This study was approved by the Human Research Ethics Committee of Murdoch
University (permit 2014/141). Full informed consent was acquired from all
participants.
Author details
1
Discipline of Chiropractic, School of Health Professions, Murdoch University,
90 South Street, Murdoch, WA 6155, Australia.
2
Discipline of Psychology,
School of Psychology and Exercise Science, Murdoch University, 90 South
Street, Murdoch, WA 6155, Australia.
Received: 5 August 2016 Accepted: 11 October 2016
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