RESEARCH ARTICLE

Brief relaxation training is not sufficient to

alter tolerance to experimental pain in
novices
Karen E. Smith1*, Greg J. Norman1,2
1 Department of Psychology, Integrative Neuroscience Area, University of Chicago, Chicago, Illinois, United
States of America, 2 Grossman Institute for Neuroscience, University of Chicago, Chicago, Illinois, United
States of America

* kelsmith@uchicago.edu

Abstract
Relaxation techniques, such as deep breathing and muscle relaxation, are aspects common
to most forms of mindfulness training. There is now an abundance of research demonstrat-
ing that mindfulness training has beneficial effects across a wide range of clinical conditions,
making it an important tool for clinical intervention. One area of extensive research is on the
beneficial effects of mindfulness on experiences of pain. However, the mechanisms of
these effects are still not well understood. One hypothesis is that the relaxation components
of mindfulness training, through alterations in breathing and muscle tension, leads to
OPEN ACCESS changes in parasympathetic and sympathetic nervous system functioning which influences
Citation: Smith KE, Norman GJ (2017) Brief pain circuits. The current study seeks to examine how two of the relaxation subcomponents
relaxation training is not sufficient to alter tolerance of mindfulness training, deep breathing and muscle relaxation, influence experiences of
to experimental pain in novices. PLoS ONE 12(5): pain in healthy individuals. Participants were randomized to either a 10 minute deep breath-
e0177228. https://doi.org/10.1371/journal.
ing, progressive muscle relaxation, or control condition after which they were exposed to a
pone.0177228
cold pain task. Throughout the experiment, measures of parasympathetic and sympathetic
Editor: Hong-Liang Zhang, National Natural
nervous system activity were collected to assess how deep breathing and progressive mus-
Science Foundation of China, CHINA
cle relaxation alter physiological responses, and if these changes moderate any effects of
Received: December 12, 2016
these interventions on responses to pain. There were no differences in participants’ pain tol-
Accepted: April 24, 2017 erances or self-reported pain ratings during the cold pain task or in participants’ physiologi-
Published: May 11, 2017 cal responses to the task. Additionally, individual differences in physiological functioning
Copyright: © 2017 Smith, Norman. This is an open were not related to differences in pain tolerance or pain ratings. Overall this study suggests
access article distributed under the terms of the that the mechanisms through which mindfulness exerts its effects on pain are more complex
Creative Commons Attribution License, which
than merely through physiological changes brought about by altering breathing or muscle
permits unrestricted use, distribution, and
reproduction in any medium, provided the original tension. This indicates a need for more research examining the specific subcomponents of
author and source are credited. mindfulness, and how these subcomponents might be acting, to better understand their util-
Data Availability Statement: All relevant data ity as a clinical treatment.
are within the Supporting Information files.

Funding: The authors received no specific funding

for this work.

Competing interests: The authors have declared

that no competing interests exist.

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 Relaxation and pain sensitivity

Introduction
Relaxation interventions, such as deep breathing or muscle relaxation, have demonstrated effi-
cacy in treating pain symptoms in patients suffering from chronic pain [1], and there is some
evidence that they are also effective in treating clinical disorders, including anxiety [2] and
depression [3]. These techniques are similar to what are termed mindfulness techniques.
While there are a range of definitions, the key distinction made between relaxation and mind-
fulness is that there is an intentional focus to relax during the practice of relaxation methods
while mindfulness involves the cultivation of a non-judgmental, moment-to-moment aware-
ness [3]. However, it is not clear how different the two types of interventions are in terms of
efficacy. Studies which have directly compared them have found relatively similar effects on
anxiety and mood [3,4]. Indeed, there has been a trend towards interventions which incorpo-
rate both mindfulness and relaxation techniques in combination, often broadly referred to as
“mindfulness based” interventions [5]. These interventions have demonstrated efficacy for
treating a wide range of disorders, including many debilitating clinical conditions, such as
depression, anxiety, borderline personality disorder, eating disorders, and chronic pain [5–8],
leading to their increasing use within clinical populations. Given the often substantial efficacy
of mindfulness interventions across a wide range of clinical conditions, many of which histori-
cally have been resistant to treatment, they offer an exciting new treatment tool within the clin-
ical community.
One area in which there has been substantial research on the efficacy of mindfulness inter-
ventions is in individuals suffering from chronic pain [9,10]. Numerous anecdotal reports and
case studies on long-term meditation practitioners have reported a significant reduction in
self-reported pain symptoms [11,12]. Because of this, there has been a wealth of research exam-
ining the utility of mindfulness interventions for alleviating chronic pain symptoms [9,13–15].
As with other clinical areas, this work suggests there are positive effects of mindfulness inter-
ventions for chronic pain patients. However, this evidence is mixed, and indeed a recent sys-
tematic literature review found that there were no added benefits of mindfulness based pain
interventions compared to cognitive and behavioral therapy alone [13]. Additionally, there is a
range in what aspects of pain experiences are positively influenced by mindfulness based inter-
ventions, with the largest effects often seen for depression or negative mood associated with
pain, while effects for self-reported pain are more mixed, with studies often finding no change
in measures asking generally about participants’ current level of pain (i.e. How much pain are
you in at the moment?) [16]. This suggests that these interventions have varying effects on dif-
ferent aspects of pain, and indicates a need for elaboration of what these aspects are and the
mechanisms through which they are influenced. In order to better understand the mechanisms
through which mindfulness produces symptom relief in chronic pain patients, it is important
to examine how these types of activities affect acute experiences of pain in healthy participants,
both at the level of nociception and self-reported experiences of pain, as well as any changes in
general perceptions of stress or mood in response to the pain.
Compared to the literature on chronic pain, there are very few studies looking at the effi-
cacy of mindfulness interventions on experiences of pain in healthy individuals [17,18]. Those
studies that do look at the efficacy of mindfulness interventions on experiences of pain in
healthy individuals have found mixed results [17,19–23]. Often these studies focus on current
practitioners of mindfulness [19,22], making it difficult to compare how effective these inter-
ventions might be with novices or even how much training is necessary to see the observed
effects. Additionally, it is possible that people who have higher tolerances for pain initially are
more likely to practice mindfulness. However, there is some evidence that short one-time
interventions may have beneficial effects in novices on nociception, or the response of the

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 Relaxation and pain sensitivity

sensory nervous system to a noxious stimulus that leads to the subjective experience of pain
[17,21,23]. This evidence is mixed though, with some research finding mindfulness increases
both pain tolerance and self-reported pain [15,23], some finding changes in only the nocicep-
tive response but not self-reported pain [21], and some finding no effects in novice participants
at all [19].
The lack of consistent results for the effects of mindfulness interventions on experiences of
pain is partially due to the variability across studies in the type of mindfulness or mindfulness
subcomponent employed. Mindfulness is commonly defined as the quality of awareness that
arises through intentionally attending to present moment experience in a non-judgmental and
accepting manner [24]. However, the procedures used to achieve mindfulness in the literature
include quite disparate practices ranging from deep breathing exercises [20,25] and muscle
relaxation [26,27] to massage [28,29] and teaching full meditation traditions [30,31]. This vari-
ability in methodology across studies has made it difficult to determine which aspects of these
interventions are associated with positive effects. Given this, it is important to investigate dif-
ferent components of mindfulness separately in order to better understand the mechanisms
through which specific components may be producing positive effects. One approach to disen-
tangling these mechanisms is to focus on the different subcomponents of these interventions
and their specific mechanisms of action.
This study aims to provide insight into the effects of different mindfulness subcomponents,
specifically focusing on two common relaxation components often employed within the con-
text of mindfulness interventions: modulating breathing through a deep breathing task and
gradual muscle relaxation through a progressive muscle relaxation task. These aspects were
chosen because they are most common across the mindfulness intervention literature, with all
practices involving some sort of instruction about slowing or attending to breathing, and
many also incorporating a type of muscle relaxation task, often in the form of a body scan.
Additionally, both of these tasks have been employed with and shown efficacy in novices
[20,21]. However, these tasks have never been directly compared, and, while they appear to be
effective at alleviating pain, the specific mechanisms through which this occurs are still
unclear. These tasks are also easier to convey to individuals unfamiliar with the techniques as
compared to more abstract aspects of mindfulness such as developing a state of nonjudgmental
awareness of cognitions and streams of thoughts. Lastly, each of these tasks involves explicit
instructions for modulating aspects of physiological function, which could influence both
nociceptive and central experiences of pain. For example, changes in breathing modulate baro-
receptor activity, stretch receptors which regulate blood pressure through alterations in sym-
pathetic and parasympathetic cardiac control [32] and have been related to differences in pain
sensitivity [33,34]. Additionally, muscle relaxation is thought to exert its effects through
decreased afferent neural impulses from the skeletal musculature resulting in decreased sym-
pathetic activity and reduced activity of neuromuscular circuits involved in the experience of
pain [35,36]. These provide a concrete mechanism through which these types of interventions
may influence individuals’ pain sensitivity.
The goal of this study was to assess how different relaxation aspects of mindfulness influ-
ence individuals’ experiences of acute pain and if they have differential effects. Additionally,
this study aimed to examine the potential mechanisms through which the different relaxation
aspects of mindfulness act. To do this, we compared the effects of a deep breathing, progressive
muscle relaxation, and an active control condition on individuals’ pain tolerance as assessed
by a cold pressor task. Throughout the study, we collected measures of cardiac parasympa-
thetic and sympathetic nervous system activity to assess whether changes within these systems
moderate any observed effects. We expect that both breathing and progressive muscle relaxa-
tion interventions will result in higher pain thresholds, We also expect that these increases will

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 Relaxation and pain sensitivity

be related to physiological changes induced by the intervention. However, in contrast with

deep breathing, we expect progressive muscle relaxation might produce a dissociation between
pain tolerance and self-reported pain, with pain tolerance increasing without comparable
changes in self-reported pain as previously observed [21].

Materials and methods

Participants
63 (24 male) University of Chicago undergraduates, ages 18–23 years (mean 20) participated
in the study (22% Asian American, 11% African American, 0.02% Middle Eastern/Arab Amer-
ican, 41% Caucasian, 19% Multiple Ethnicities, 0.05% Other Ethnicity). Sample size was com-
parable to that in previous studies [20–23]. The participants were provided monetary or
course credit compensation for their participation. Participants gave written informed con-
sent, and this study was approved by the University of Chicago’s Institutional Review Board
and conducted in accordance with the Declaration of Helsinki.

Procedure
After arrival at the laboratory, participants were consented for the study and sensors were con-
nected for all physiological measures. Participants then sat quietly for 5 minutes as an initial
baseline assessment of physiological measures. After this baseline period, participants com-
pleted a set of questionnaires assessing demographics and current psychological state. Partici-
pants were then assigned to one of three 10 minute experimental conditions: deep breathing,
progressive muscle relaxation, or a control condition. After the experimental condition, partic-
ipants completed a short set of post-questionnaires. Participants then performed a cold pressor
task.

Questionnaire measures
Participants completed six questionnaires prior to undergoing the experimental condition,
which included a demographic questionnaire; the State and Trait Anxiety Index (STAI) [37], a
20-item scale assessing individuals’ levels of state and trait anxiety; the Perceived Stress Scale
(PSS) [38], a 10-item scale assessing individuals’ perception of stress, control, and predictabil-
ity over life events in the past month; the Center for Epidemiological Studies—Depression
Scale (CESD) [39], a 20-item scale assessing individuals’ feelings of depression; the UCLA
Loneliness Scale [40], a 20-item scale assessing individuals’ perceptions of loneliness; and the
Body Perceptions Questionnaire [41], a 122 item scale aimed at assessing individuals’ aware-
ness of different body processes. Post experimental condition, participants again completed
the PSS and the Trait portion of the STAI to assess any changes in perceived stress and anxiety
after the different breathing conditions.

Conditions
Participants were randomly assigned to one of three 10 minute experimental conditions: deep
breathing, progressive muscle relaxation, or control condition. During the deep breathing con-
dition, participants were instructed to match their breathing to a moving dot on the presenta-
tion—inhaling with the dot as it moved up, pausing as the dot remained flat, and exhaling as
the dot moved down. This task was modeled upon previous deep breathing tasks [20,42,43]
and was designed to reduce breathing to 5 breaths per minute. The progressive muscle relaxa-
tion consisted of a 10 minute audio segment, taken from one previously employed [21], during
which participants were instructed to progressively tense and relax different muscle groups,

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 Relaxation and pain sensitivity

while breathing deeply throughout. Lastly, in the control condition, participants were
instructed to only watch the moving dot from the breathing condition without any explicit
instruction to change breathing.

Cold pressor
During the cold pressor, participants immersed their left foot in circulating cold water and ice
slush maintained at 0˚C. Participants were told to remove their foot when they could no longer
tolerate the pain. If participants had not removed their foot by 5 minutes, the task ended, and
the experimenter asked the participants to remove their foot. Previous work has utilized time
cutoffs between 1–5 minutes [23,44–47]. We chose 5 minutes as a cutoff to ensure there was
significant variability in participants’ pain tolerances—the length they were able to keep their
foot in the water—as this was our primary outcome of interest. The amount of time (mm:ss)
the participants kept their foot in the water was used as a measure of pain tolerance [48]. Addi-
tionally, participants were asked to rate the amount of pain they were experiencing every 30
seconds using a Visual Analogue Scale (from no pain to the worst imaginable pain), as has
been employed previously [48]. The cold pressor task was only conducted once, post experi-
mental condition, to avoid any potential habituation effects to the paradigm and to avoid
inducing a state of stress in participants, via exposure to pain, prior to completing the experi-
mental task.

Physiological measures
Cardiovascular measures of sympathetic and parasympathetic cardiac control were derived
from impedance cardiography (pre-ejection period (PEP)) and an electrocardiogram (high
(respiratory) frequency (0.12–0.42 Hz) heart rate variability (HF HRV)). Data were scored
minute by minute and then collapsed for each task.
PEP, derived from impedance cardiography, is the period between the electrical stimulation
of the ventricular myocardium (Q wave of ECG) and the opening of the aortic valve. As PEP
depends on the time development of intraventricular pressure, it is used as an index of cardiac
contractility. Given variations in contractility are primarily under sympathetic control, PEP is
used as a noninvasive measure of sympathetic influence of the heart [49,50]. Lower PEP values
(in ms) represent higher levels of sympathetic activity. HF HRV is a rhythmic fluctuation of
heart rate in the respiratory frequency band (respiratory sinus arrhythmia (RSA)) and has
been demonstrated to be a relatively pure index of parasympathetic cardiac control [51].
The impedance cardiogram was collected using a four spot electrode configuration [52].
The electrocardiogram (ECG) was collected using the standard lead II configuration. The ECG
and basal thoracic impedance (Z0) were measured using a Bionex system (MindWare Tech-
nologies LTD, Gahanna, OH). MindWare software was used to visually inspect all physiologi-
cal data and to analyze the dZ/dt waveforms to obtain PEP from impedance. HR HRV was
derived from ECG using spectral analysis of the interbeat interval series. The interbeat interval
series was time sampled at 4 Hz (with interpolation) to yield an equal interval time series. This
time series was detrended (second-order polynomial), end tapered, and submitted to a fast
Fourier transformation. HF HRV spectral power was then integrated over the respiratory fre-
quency band (0.12–0.42 HZ) and HF HRV is represented as the natural log of the heart period
variance in the respiratory band (in ms2).

Statistical analysis
To examine changes in the physiological measures and state anxiety and perceived stress over
the course of the study by condition, repeated measures (time X condition) ANOVAs were

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 Relaxation and pain sensitivity

run for each outcome measure. The sample size was determined to evidence a large effect size
at 80% statiscal power.
To assess whether there were any differences between conditions in the amount of time
individuals kept their foot in the water, a Cox proportional hazards regression model was run.
For cold-pressor endurance time, foot withdrawal was defined as an event and individuals
who endured the full 5 minutes were treated as censored in the analysis. We incorporated pos-
sible covariates into the models in a stepwise manner. To determine the power of the current
data to detect an effect the size of any observed effects, we created simulated data sets from the
current models and tested the proportion of simulated data sets the size of the observed effect.

Results
Sample composition
Of the 63 participants, 11 were excluded due to failure to completely submerge their foot in
the water bath or confusion when taking their foot out resulting in inaccurate timing data. For
the remaining 53 participants, 17 students were assigned to the breathing condition, 15 to the
control, and 21 to the progressive muscle relaxation condition. Participants did not differ sig-
nificantly on gender, age, income or ethnicity across conditions. Participants also did not differ
significantly for depression, loneliness, trait and initial state anxiety, or initial stress across
conditions.

Questionnaire measures
For state anxiety and perceived stress, 2 (pre/post manipulation) X 3 (condition) within sub-
jects repeated measures ANOVAs were run to assess whether there were any changes in either
measure after the manipulation. There was a significant main effect of time (pre/post) for state
anxiety (F(1,51) = 7.91, p < 0.01), indicating a significant increase in participants’ anxiety after
the task (Fig 1). There was no main effect of condition (F(2,51) = 0.88, p = 0.418) or interaction
between condition and time (F(2,51) = 0.88, p = 0.420), suggesting condition had no influence
on participants’ anxiety levels.
For perceived stress, there was also a significant main effect of Time (F(1,50) = 18.91,
p < 0.001), with participants’ perceived stress decreasing after the manipulation (Fig 1). How-
ever, again there was no significant main effect of condition (F(2,50) = 1.46, p = 0.243) or sig-
nificant interaction effect between condition and time (F(2,50) = 0.63, p = 0.537). Overall this
suggests that while participants’ levels of perceived stress decreased over time, there were no
differences in this change by condition, and participants’ anxiety levels did not change over
the course of the experiment.

Physiological measures
For mean heart rate, HF-HRV, respiration, and PEP, average values were calculated for the
baseline period, condition period, and cold pressor. Using these values, 3 (baseline, condition,
cold pressor) X 3 (condition) repeated measures ANOVAs were run to assess any changes in
physiology over time by condition. For all measures but PEP, there was a significant effect of
time on physiological change (HR: F(2,100) = 46.82, p < 0.001; HF-HRV: F(2,100) = 3.89,
p < 0.05; Respiration: F(2,100) = 10.48, p < 0.001; PEP: F(2,96) = 0.75, p = 0.476; Fig 2). Post-
hoc analyses suggested that these effects were driven by a significant increase between inter-
vention (M = 74.64) and cold pressor (M = 83.03; Fisher-Hayter p < 0.001) for heart rate, a sig-
nificant decrease between baseline (M = 6.66) and cold pressor (M = 6.31; Fisher-Hayter
p < 0.01) for HF-HRV, and a significant increase between intervention (M = 16.52) and cold

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 Relaxation and pain sensitivity

Fig 1. Effects of intervention on perceived anxiety and stress. (A) Perceived anxiety significantly
increased over time, and (B) perceived stress significantly decreased, but there were no significant effects of
intervention type on change in scores over time.
https://doi.org/10.1371/journal.pone.0177228.g001

pressor (M = 18.26; Fisher-Hayter p < 0.001) for respiration. For all physiological measures,
there was no main effect of condition (HR: F(2,50) = 2.28, p = 0.112; HF-HRV: F(2,50) = 2.39,
p = 0.102); Respiration: F(2,50) = 0.79, p = 0.461; PEP: F(2,48) = 1.51, p = 0.231). For
HF-HRV, however, there was a significant condition by time interaction (F(4,100) = 4.44, p
< 0.01). Post hoc analysis indicated this was due to a significant decrease (Fisher-Hayter p
< 0.05) in HF-HRV between intervention (M = 6.70) and cold pressor (M = 5.87) for the
breathing group, while both for the control and PMR groups there were no significant post-
hoc comparisons, indicating they remained stable across all tasks. There were no significant
interactions for any of the other physiological measures (HR: F(4,100) = 0.38, p = 0.822; Respi-
ration: F(4,100) = 2.11, p = 0.085; PEP: F(4,96) = 0.44, p = 0.777). Overall this suggests that the
cold pressor induced significant increases in respiration and heart rate, and decreases in
HF-HRV, as would be expected, but neither the breathing manipulation nor PMR produced

Fig 2. Effects of intervention on cardiac measures and respiration. Effects of intervention on cardiac
measures and respiration: (A) Respiration, (B) Heart Rate, (C) HF-HRV, (D) PEP. There were no significant
effects of intervention on any of the measures.
https://doi.org/10.1371/journal.pone.0177228.g002

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 Relaxation and pain sensitivity

significant differences in individuals’ physiological responses to the manipulation or cold

pressor.

Cold pressor
The initial Cox regression, incorporating just condition as a predictor of hazard produced no
significant effects (Hazard Ratio = 0.991, p = 0.962), indicating that condition did not influ-
ence participants’ pain tolerance. To examine whether pain tolerance may be influenced by
participants’ perceived pain, and whether perceived pain ratings interact with condition to
produce differences in pain tolerance, we next incorporated pain ratings into the Cox regres-
sion model as a time-varying variable. This model did indicate a significant effect of perceived
pain on pain tolerance (Hazard Ratio = 1.04, p < 0.01), suggesting participants with higher
perceived pain are more likely to remove their foot from the water earlier, but this model did
not change the effect of condition (Hazard Ratio = 1.52, p = 0.503), and there was no interac-
tion effect (Hazard Ratio = 0.993, p = 0.507). The model incorporating both pain ratings and
condition as predictors was a worse fit than modeling pain ratings alone.
As it was also hypothesized that changes in physiological measures due to the manipulation
would influence participants’ pain tolerance, change scores between baseline and breathing
conditions were calculated and incorporated into the model as time invariant variables. These
produced no significant effects and did not change the effect of condition or improve overall
model fit, suggesting that individual differences in physiological responsivity to the manipula-
tion did not contribute to participants’ tolerance for pain (For all model specifications and
results see S1 Appendix and S1 Table respectively).
While our simulated data sets demonstrated sufficient power for the observed null effect,
this did not answer the question of whether we have sufficient power to observe a potential
non-null effect if present. Given this concern, we also ran an ANOVA, for which we had suffi-
cient power, to assess the effect of experimental condition on pain tolerance. Similarly to the
survival analyses, we found no significant effects of condition on pain tolerance.

Discussion
This study focused on illuminating the specific mechanisms through which subcomponents of
mindfulness contribute to changes in pain tolerance and pain ratings. In contrast to previous
research [1,20,21], we found no evidence for two relaxation subcomponents of mindfulness, in
the form of deep breathing and PMR, altering individuals’ pain tolerance or self-reported pain.
We also did not find any support that these types of interventions, at least within the context
of a brief intervention, have physiological effects which contribute to individual differences in
responses to the intervention. Overall, this suggests that a short term relaxation or focused
breathing is not sufficient to influence participants’ experiences of pain.
There are several potential reasons why this study did not find expected differences in pain
tolerance due to relaxation based manipulations. One explanation is that changing breathing
and muscle relaxation simply do not influence experiences of pain. There is some evidence
that deep breathing tasks that require attention (e.g. matching breaths to a visual stimulus, as
employed in this task) do not significantly change pain thresholds, while those described as
more relaxing, having individuals internally pace their breaths with audio instruction but no
visual attention required, do significantly alter pain thresholds [20]. However, this does not
explain the lack of difference across conditions in pain ratings, anxiety, and perceived stress
changes, as the same study found both the attentive and relaxing intervention induced similar
mood changes [20]. Nor does this explain the lack of effect for PMR, which rather than focus-
ing on just changing breathing, focuses on changing muscle tension with brief reminders

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 Relaxation and pain sensitivity

throughout the audio about to remember to breath but no specific instruction on how to alter
breathing. Additionally, PMR has been demonstrated to be more reliably effective than other
relaxation interventions in the context of chronic pain and injury pain [1], significantly influ-
ence nociceptive responses in novices [21], and modulate sympathetic responsivity [35].
Importantly, however, it is difficult to generalize and compare the findings in this study to
those with chronic pain patients who experience long-term persistent pain in a naturalistic set-
ting which has real threat value for these patients. This study employed a short term interven-
tion in the context of an acute laboratory pain stimulus with no real threat value to healthy
volunteers. Nonetheless, this still does not explain the lack of consistency in findings with stud-
ies that looked at nociceptive responses in novices [20,21].
A more likely explanation is that the intervention time period was too short to have an
effect. While there have been a few studies which examined similarly short one-time interven-
tions with novices and found some significant effects [25,53], the majority of studies address-
ing the question of whether relaxation interventions or mindfulness based training
incorporating these aspects of relaxation influence experiences of pain have been conducted
with long-term repeated intervention over the course of several weeks (most common 8 week
intervention) [1,9]. It is likely that even in the case of the most basic type of relaxation, i.e., a
focus on breathing, this initially requires effort and attention on the part of the individual,
making it less relaxing, and after practice it becomes more automatic. Indeed, while there was
a pattern towards decreased breathing rates in the breathing task condition, the fact there is
not a significant condition by time interaction for respiration, suggests that the intervention
was not as effective as expected.
It is also possible that relaxation tasks alone are not sufficient to induce changes in pain tol-
erance. Many of the mindfulness based interventions that have demonstrated effects on experi-
mentally induced pain focus on changes in breathing in combination with teaching acceptance
and awareness exercises [9,23]. These aspects may be key to modulating individuals’ experi-
ences with pain. Indeed, it has been hypothesized that many of the effects of mindfulness/med-
itation interventions act through a cognitive restructuring, changing attention and self-
regulatory processes [24,54]. However, more research is necessary to better understand the
underlying neurobehavioral mechanisms through which these changes may be occurring [55].
Additionally, it is the case that these relaxation interventions alone, especially PMR, have pre-
viously demonstrated efficacy in altering perceptions of pain [1], making it more likely that the
lack of effects are due to length of the intervention. Given the lack of consistency of activities
across mindfulness interventions and their efficacy, it is important for future research to eluci-
date which aspects of these interventions are most important to achieving changes in not only
pain, but also in other areas in which they are employed. Lastly, it is possible that the lack of
effect was a result of a small sample size. However, our sample was comparable to that of previ-
ous studies that have found effects [20–23], and when analyses were re-run using a 3-way
ANOVA comparing mean pain tolerance times, for which we had sufficient power (0.80) to
detect a medium effect with our sample size, we still found no differences across conditions for
participants pain tolerance. Despite this, future work should replicate and extend these find-
ings with a larger sample size.
Overall this study provides no evidence for the hypothesis that changing breathing, com-
mon to most mindfulness interventions, is the key mechanism through which these interven-
tions modulate individuals’ experiences of pain. Indeed we were unable to replicate any
previous effects of either deep breathing or PMR on pain tolerance [20,21,25]. However,
despite this, this study provides several important contributions to the understanding of relax-
ation interventions in the context of mindfulness. First, we have demonstrated that this brief
of an intervention, 10 minutes, is not likely to have any large effects on novices’ experiences of

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 Relaxation and pain sensitivity

pain, establishing a lower bound for efficacy of these types of interventions. Additionally, it
suggests that the mechanisms involved in the beneficial effects of mindfulness interventions,
are likely more complex than simply focusing on breathing or muscle tension thereby exerting
physiological changes which then act to influence nociception and perceptions of pain. Given
that these types of interventions are employed in treatment for a wide range of ailments, rang-
ing from acute pain to depression to borderline personality disorder to supporting children
experiencing early childhood trauma, it is important that more work focuses on what aspects
of different mindfulness, meditation, and relaxation interventions, through direct comparison
in a randomized control setting, actually contribute to observed effects on acute pain, as well
as how long and how much practice is necessary to achieve these effects, in order to better
understand the utility of different aspects of mindfulness as an intervention for experiences of
pain, and more broadly their utility for treatment of a wide range of disorders.

Supporting information
S1 Appendix. Cox regression models.
(DOCX)
S1 Data. Data set used in manuscript.
(XLSX)
S1 Table. Cox regression model results: No significant effects of intervention, but pain rat-
ings demonstrated a significant effect for people with higher pain ratings having faster
time to removal of food from the water. Model A: Included only intervention as predictor;
Model B: Included only pain ratings as predictor; Model C: Included intervention and pain
ratings as predictors; Model D: Included intervention, pain ratings, change in PEP, RSA, HR
and respiration from baseline to intervention, and baseline RSA as predictors. p < 0.05,
p < 0.01, p < 0.001.
(DOCX)

Author Contributions
Conceptualization: KES GJN.
Data curation: KES.
Formal analysis: KES GJN.
Investigation: GJN.
Methodology: KES GJN.
Project administration: KES GJN.
Resources: GJN.
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