Physical Exercise and Chronic Pain in University Students: A1111111111 A1111111111 A1111111111 A1111111111 A1111111111
Physical Exercise and Chronic Pain in University Students: A1111111111 A1111111111 A1111111111 A1111111111 A1111111111
Physical Exercise and Chronic Pain in University Students: A1111111111 A1111111111 A1111111111 A1111111111 A1111111111
RESEARCH ARTICLE
Abstract
OPEN ACCESS
frequency, intensity and duration of physical exercise, and chronic pain, and if sociodemo-
graphic, lifestyle or other health factors could explain any of the observed associations.
Independent variables
Physical exercise. First, the following brief definition of physical exercise was presented
to the students: “With exercise, we mean that you, for example, go for a walk, go skiing, swim or
take part in a sport”. Exercise was then assessed using three sets of questions, including the
average number of times exercising each week, and the average intensity and average hours
each time [27]: 1) “How frequently do you exercise?” (Never, Less than once a week, Once a
week, 2–3 times per week, Almost every day); 2) “If you exercise as frequently as once or more
times a week: How hard do you push yourself? (I take it easy without breaking into a sweat or
losing my breath, I push myself so hard that I lose my breath and break into a sweat, I push
myself to near-exhaustion); and 3) “How long does each session last?” (Less than 15 minutes,
15–29 minutes, 30 minutes to 1 hour, More than 1 hour”. This 3-item questionnaire has previ-
ously been used in the large population-based Nord-Trøndelag Health Study (HUNT) [27,
28]. In the current study, the response options “Never” and “Less than once a week” were com-
bined for the frequency item, constituting the reference category. For the duration item, the
response options “Less than 15 minutes” and “15–29 minutes” were also combined for the
same reasons. Detailed information on the physical exercise items in the SHoT2018 study has
been published elsewhere [29]. Previous validation studies [27, 28] have demonstrated moder-
ate correlations between these questionnaire items and direct measurement of VO2max during
maximal work on a treadmill (r = 0.43[frequency], r = 0.40 [intensity] and r = 0.31 [duration]),
with ActiReg [30, 31] (an instrument that measures PA and energy expenditure), and with the
International Physical Activity Questionnaire [32].
Dependent variables
The Graphical Index of Pain (GRIP). GRIP is a hierarchical digital body map designed
to assess pain and pain-related characteristics [16]. The instrument consists of 10 first-tier
regions (head, neck, left arm, right arm, upper and lower back, left leg, right leg, chest, abdo-
men, genitals/pelvic floor/urethra/anus) followed by anatomical sites at second-tier (167 loci
among men and 168 loci among women). Participants were asked to report pain experienced
within the last 4 weeks, omitting brief transient pain. Pain characteristics were reported for
each of the marked first-tier regions, i.e. pain duration, episode frequency, episode duration,
intensity, how bothersome the pain was, and interference with daily activities and sleep.
Women were instructed not to report menstrual pain. Instructions and questions in GRIP
were put in Norwegian. Translation to English was made by a certified translator, but back
translation is still in process [16].
Chronic pain. The definition of chronic pain was based upon the ICD-11 criteria, with
pain persisting or recurring for longer than 3 months [33]. In GRIP, subjects reported the time
since first onset of pain. The options were: “Less than 4 weeks”, “1–2 months”, “3–5 months”,
“6–11 months”, “1–2 years”, “3–5 years”, “More than 5 years (asked about the age of onset)”.
Hence, the chronic pain definition in the present study was pain experienced within the last 4
weeks in at least one of ten first tier loci with �3 months duration. For purposes of the present
study, the GRIP was used to produce several heat maps to visualize the prevalence and distri-
bution of chronic pain.
Moderate to severe chronic pain. The ICD-11 definition of moderate to severe chronic
pain is based on three pain-related parameters [33]: a) pain intensity, b) pain-related distress
and c) task interference. The assessment may be graded on a 100-mm visual analogue scale
(VAS) (4). The participants in SHoT2018 were asked to grade the following pain characteris-
tics on a VAS (from 0 to 10): a) pain intensity (anchors: No pain/The strongest imaginable
pain), b) bothering as a proxy of pain-related distress (anchors: No bother/The greatest imag-
inable bother), and c) impact on activity in daily activities, as a proxy of task interference
(anchors: Not at all /Can’t do anything) (4). We regarded that moderate to severe chronic pain
was present in subjects reporting pain within the last 4 weeks in at least one of 10 first tier
body regions, with the onset of �3 months, and with pain intensity of VAS �4, bothering of
VAS �4, and impact on daily activities of VAS �4.
Control variables
Sociodemographic information. All participants reported their gender, age and relation-
ship status (coded as single versus married/partner or girl-/boyfriend). Economic activity was
coded dichotomously according to self-reported annual income (before tax and deductions,
and not including loans and scholarships): “economically active” (annual income > 10,000
NOK) versus “economically inactive” (� 10,000 NOK). Finally, participants were categorized
as an immigrant if either the participants or one or both of his/her parents were born outside
Norway.
Body Mass Index (BMI). BMI was calculated based on self-reported body weight (kg)
divided by self-reported squared height (m2), and categorized as underweight (BMI < 18.5),
normal weight (BMI 18.5–24.9), overweight (BMI 25.0–29.9) and obesity (BMI � 30). Trend
data on overweight and obesity from the SHoT studies have been published elsewhere [29].
Sleep duration. The participants’ self-reported usual bedtime and wake up time were
indicated in hours and minutes, and data were reported separately for weekdays and week-
ends. Time in bed (TIB) was calculated as the difference between bedtime and wake up time.
Sleep onset latency (SOL) and wake after sleep onset (WASO) were also indicated separately
for weekdays and weekends in hours and minutes. Sleep duration was defined as TIB minus
SOL and WASO. More detailed information about the sleep inventory in SHoT2018 has been
published elsewhere [34].
Statistical analyses
The heat maps were created in R (version 3.6.1; https://www.r-project.org) with functions
to create vector graphics to color loci of the GRIP images, based on values in the input data
matrix. IBM SPSS Statistics 25 for Windows (SPSS Inc., Chicago, IL) was used for the other
analyses. Pearson’s chi-squared tests were used to examine differences in the prevalence of
pain by physical exercise level, stratified by gender. Logistic regression models were computed
to obtain effect-size estimates for the dichotomous dependent variables. Results are presented
as odds-ratios (ORs) with 95% confidence intervals. We computed one unadjusted and two
adjusted models. In the first block we controlled for socio-demographic factors (categorical),
body-mass index (continuous), alcohol use and problems (AUDIT continuous sum score),
and sleep duration (continuous). In the second block (fully adjusted model) we additionally
adjusted for self-reported depression. Estimated marginal means (EMM) were also computed
to examine exercise frequency against number of pain loci, adjusting for age. Missing values
were handled using listwise deletion.
Ethics
All procedures involving human subjects/patients were approved by the Regional Committee
for Medical and Health Research Ethics in Western Norway (no. 2017/1176 [SHOT2018]).
Electronic informed consent was obtained after the participants had received a detailed intro-
duction to the study.
Results
Sample characteristics
In all, 36625 students (67.2% women [n = 24600] and 32.8% men [n = 12025]) with a mean
age of 23.2 years, completed both the main SHOT2018 questionnaire and the additional GRIP
instrument. Approximately half of the students were single, 87% had no additional income
besides students’ loan and scholarships, while 8% were of non-Norwegian ethnicity. More
details of sociodemographic and clinical characteristics are listed in Table 1.
https://doi.org/10.1371/journal.pone.0235419.t001
Fig 1. Prevalence and distribution of chronic pain by the average weekly frequency of physical exercise in men and women.
https://doi.org/10.1371/journal.pone.0235419.g001
intensity of the physical exercise among females, there were no clear or strong trends regarding
the odds of chronic pain. In contrast, the duration of the exercise was inversely associated with
reporting more pain: female students exercising more than 1 hour a week were around 20%
less likely to report chronic pain compared to students exercising hour less than 30 minutes a
week (fully adj. OR = 0.83, 95% CI: 0.75–0.92).
Similar trends were observed among male students, but the beneficial effects were overall
higher (lower ORs) than for females, especially regarding the frequency of physical exercise. In
contrast to female students, there was a significant inverse dose-response relationship between
exercise intensity and chronic pain among male students. This pattern was also observed for
exercise duration; the longer duration of the exercise, the lower odds for chronic pain. Overall,
adjusting for the potential confounding factors had little effect on the magnitude of the associ-
ations (Table 2).
Table 2. Association between physical exercise and chronic pain in male and female university and college and university students.
ICD-11 chronic pain
Unadjusted model Adjusted model§ Fully adjusted model#
n (%) OR 95% CI OR 95% CI OR 95% CI
Women
Physical exercise (frequency)
Never/less than once a week 2352 (63.5) 1.00 1.00 1.00
Once a week 2501 (61.7) 0.92 (0.83–1.01) 0.94 (0.85–1.04) 0.96 (0.90–1.00)
2–3 times per week 6719 (59.6) 0.85 (0.78–0.92) 0.88 (0.81–0.96) 0.92 (0.84–0.99)
Almost every day 3155 (57.2) 0.77 (0.70–0.84) 0.81 (0.74–0.89) 0.85 (0.77–0.93)
Physical exercise (intensity)
I take it easy without breaking into a sweat or losing my breath 2902 (64.2) 1.00 1.00 1.00
I push myself so hard that I lose my breath and break into a sweat 10072 (58.8) 0.79 (0.74–0.85) 0.81 (0.75–0.87) 0.83 (0.77–0.90)
I push myself to near-exhaustion 1200 (61.3) 0.89 (0.80–1.00) 0.89 (0.79–0.99) 0.92 (0.81–1.03)
Physical exercise (duration)
Less than 30 minutes 1774 (64.4) 1.00 1.00 1.00
30 minutes to 1 hour 8034 (59.6) 0.80 (0.72–0.88) 0.81 (0.74–0.89) 0.83 (0.76–0.92)
More than 1 hour 4371 (59.3) 0.78 (0.71–0.86) 0.80 (0.73–0.89) 0.83 (0.75–0.92)
Men
Physical exercise (frequency)
Never/less than once a week 1151 (49.5) 1.00 1.00 1.00
Once a week 758 (44.0) 0.79 (0.69–0.90) 0.81 (0.70–0.92) 0.83 (0.73–0.95)
2–3 times per week 1955 (41.3) 0.70 (0.63–0.78) 0.71 (0.64–0.79) 0.74 (0.66–0.82)
Almost every day 1239 (38.7) 0.63 (0.57–0.71) 0.65 (0.59–0.74) 0.69 (0.61–0.77)
Physical exercise (intensity)
I take it easy without breaking into a sweat or losing my breath 764 (46.6) 1.00 1.00 1.00
I push myself so hard that I lose my breath and break into a sweat 3232 (41.8) 0.82 (0.73–0.92) 0.84 (0.75–0.94) 0.85 (0.76–0.86)
I push myself to near-exhaustion 755 (40.0) 0.75 (0.65–0.86) 0.75 (0.65–0.86) 0.77 (0.67–0.89)
Physical exercise (duration)
Less than 30 minutes 540 (45.3) 1.00 1.00 1.00
30 minutes to 1 hour 2011 (43.5) 0.91 (0.80–1.04) 0.89 (0.78–1.02) 0.92 (0.80–1.05)
More than 1 hour 2200 (40.5) 0.80 (0.70–0.91) 0.80 (0.70–0.92) 0.83 (0.72–0.95)
§
Adjusted for socio demographics, body-mass index, alcohol use and problems and sleep duration
#
Additional adjustment for self-reported depression
https://doi.org/10.1371/journal.pone.0235419.t002
short exercise durations (<30 minutes) had more pain locations than those exercising either
30 minutes to 60 minutes, or more than one hour a week (Fig 2—panels 2E and 2F).
Discussion
This current study has several noteworthy findings. First, the prevalence of chronic pain was
high, especially among women, with more than half of the students reporting at least one
chronic pain location. With some gender differences, the overall pattern was an inverse dose-
response association between exercise and chronic pain: the more frequent, harder or longer
the exercise, the lower the odds of chronic pain. Similar findings were generally also observed
for the number of pain locations: frequent exercise was associated with fewer pain locations.
Adjusting for demographical, lifestyle factors and depression had little effect on the magnitude
of the associations.
Table 3. Association between physical exercise and moderate to severe chronic pain in male and female university and college and university students.
ICD-11 moderate to severe chronic pain
Unadjusted model Adjusted model§ Fully adjusted model#
n (%) OR 95% CI OR 95% CI OR 95% CI
Women
Physical exercise (frequency)
Never/less than once a week 858 (23.2) 1.00 1.00 1.00
Once a week 801 (19.8) 0.84 (0.74–0.94) 0.89 (0.79–0.99) 0.91 (0.81–1.03)
2–3 times per week 2124 (18.8) 0.79 (0.71–0.87) 0.85 (0.77–0.94) 0.90 (0.81–0.99)
Almost every day 918 (16.6) 0.67 (0.60–0.75) 0.74 (0.67–0.83) 0.79 (0.70–0.88)
Physical exercise (intensity)
I take it easy without breaking into a sweat or losing my breath 1037 (23.0) 1.00 1.00 1.00
I push myself so hard that I lose my breath and break into a sweat 3043 (17.8) 0.74 (0.68–0.80) 0.76 (0.69–0.82) 0.79 (0.72–0.86)
I push myself to near-exhaustion 413 (21.1) 0.90 (0.79–1.03) 0.91 (0.79–1.04) 0.94 (0.82–1.08)
Physical exercise (duration)
Less than 30 minutes 634 (23.0) 1.00 1.00 1.00
30 minutes to 1 hour 2419 (18.0) 0.74 (0.66–0.82) 0.77 (0.69–0.86) 0.80 (0.72–0.89)
More than 1 hour 1440 (19.5) 0.81 (0.72–0.90) 0.85 (0.76–0.95) 0.89 (0.79–0.99)
Men
Physical exercise (frequency)
Never/less than once a week 227 (9.8) 1.00 1.00 1.00
Once a week 117 (6.8) 0.65 (0.51–0.83) 0.70 (0.55–0.89) 0.73 (0.57–0.93)
2–3 times per week 284 (6.0) 0.57 (0.47–0.69) 0.61 (0.50–0.74) 0.65 (0.53–0.78)
Almost every day 220 (6.9) 0.67 (0.55–0.82) 0.74 (0.60–0.81) 0.79 (0.65–0.98)
Physical exercise (intensity)
I take it easy without breaking into a sweat or losing my breath 141 (8.6) 1.00 1.00 1.00
I push myself so hard that I lose my breath and break into a sweat 508 (6.6) 0.72 (0.59–0.88) 0.77 (0.62–0.94) 0.80 (0.65–0.98)
I push myself to near-exhaustion 133 (7.0) 0.76 (0.59–0.98) 0.79 (0.61–1.03) 0.83 (0.64–1.08)
Physical exercise (duration)
Less than 30 minutes 105 (8.8) 1.00 1.00 1.00
30 minutes to 1 hour 319 (6.9) 0.75 (0.59–0.95) 0.75 (0.59–0.86) 0.79 (0.62–1.00)
More than 1 hour 360 (6.6) 0.70 (0.56–0.89) 0.72 (0.56–0.91) 0.76 (0.60–0.97)
§
Adjusted for socio demographics, body-mass index, alcohol use and problems and sleep duration
#
Additional adjustment for self-reported depression
https://doi.org/10.1371/journal.pone.0235419.t003
The observed prevalence of chronic pain in the current study was even higher than what
has been observed in similar studies. In a recent review and meta-analysis of chronic pain in
epidemiological studies, a pooled chronic pain prevalence of 31% was reported, although the
authors concluded that the lack of consistency in defining chronic pain makes evaluations and
comparisons across study populations difficult [2]. A systematic review of previous studies
reporting on the link between exercise and low back pain concluded that most studies in this
field have failed to find a significant relationship between the two [40]. While this may indeed
be the case for low back pain, it has been speculated that significant associations may be con-
cealed due to crude measurements of both pain and exercise, as well as other methodological
shortcomings [41]. To our knowledge, only Landmark and colleagues [9], using detailed
exercise data from the large HUNT3 study from 2006–2008, have examined the link between
frequency, duration, and intensity of recreational exercise and chronic pain. Although the
HUNT3 study includes a substantial proportion of older adults (65+ years), subgroup analyses
Fig 2. Association between physical exercise frequency (top), intensity (middle) and duration (bottom) and number of ICD-11 chronic pain loci (left) and
number of ICD-11 moderate to severe chronic pain loci (right) for male (red) and female (green) students at Norwegian colleges and universities. Boxes
represent estimated marginal means (EMM; adjusted for age), and error bars represent 95% confidence intervals.
https://doi.org/10.1371/journal.pone.0235419.g002
of participants aged 20–64 years revealed a U-shaped association between exercise frequency
and chronic pain. In contrast, the current study found this association to be linear; the more
frequent the weekly exercise, the lower the risk of chronic pain. There may be several possibili-
ties for these divergent findings, but we cannot disregard the possibility that differences in
both sample composition and pain assessment, may play a role. Specifically, the assessment
of chronic pain in the current study included a more thorough assessment, compared to the
briefer 2-items pain inventory used in the HUNT3 study. Of importance, in a smaller longitu-
dinal follow-up study of 6419 participants in the HUNT-3 study, Landmark et al. [10] found
that regular exercise at baseline was associated with less pain over a 12 month follow-up
period. However, the relationship was substantially reduced when controlling for baseline pain
and was only significant for men. Concluding that the associations were close in time and
weak, the Landmark et al. studies show that the significance of the exercise-pain link remains
open for discussion. As such, the current national study of young adults, extending on previ-
ous evidence by using detailed instruments of both pain and exercise, suggest that there is
indeed a significant association, and stronger in magnitude than previously believed, between
reduced activity and risk of chronic pain.
The findings from the current study have some important clinical and public health impli-
cations. Both sedentary behavior [42] and pain [3] are some of our biggest public health chal-
lenges in the general population. The increasing level of inactivity has led the World Health
Organization (WHO) to launch a global action plan [43] on physical activity for 2018 to 2030
in an attempt to make the world’s population more active. This action plan aims at providing
a system-based framework of effective and practical policy actions to countries in order to
increase physical activity at all levels, emphasizing the need for a paradigm shift. Moreover,
colleges and universities should to a larger extent, consider facilitating their students to take
part in sports and exercise, perhaps also by having physical exercise become more integrated
into the college environment.
In terms of future research, there is a need to conduct well-controlled and prospective stud-
ies to explore if, or to what extent, we can prevent chronic pain by increasing our level of phys-
ical exercise. It is also important to examine this across populations, both in terms of different
age cohorts, and in healthy versus clinical samples. As also emphasized by Landmark et al.
[10], identifying specific groups that may benefit more from exercise interventions to reduce
the risk of chronic pain and improve health in general, would be an important objective for
future investigations.
Methodological considerations
The most important limitation of the current study is the cross-sectional nature of the study,
limiting our ability to study the directionality between physical exercise and chronic pain. As
such, inactivity may be both a risk factor, as well as a consequence of chronic pain. Another
important limitation is the modest response rate, with little information about the characteris-
tics of non-participants beyond age and gender distribution. Selective participation could bias
the prevalence observed to the extent the selection was correlated with reports of chronic pain.
On the one hand, it has been shown that non-participants of health surveys in general have
poorer health than participants [44]. The current results may, therefore, represent an underes-
timation of the true prevalence of chronic pain in the target population. On the other hand,
people are in general more prone to participate in a survey if the topic is relevant to them per-
sonally [45]. As the information material of the SHoT2018-study focused much on “how the
students really are and feel”, one may speculate if this would lead to a higher participation rate
of individuals who felt that the topic was of particular relevance to them. Since response rates
are particularly important in prevalence studies, care should be taken when generalizing
the current findings to the whole student population. Rather, it may be more appropriate to
emphasize the relative differences between men and women, as these estimates are less prone
to selection bias. Using a web-based survey approach may have contributed to the modest
response rate, as electronic platforms have been shown to yield somewhat lower participation
rates compared to traditional approaches [46, 47]. However, there are also reports showing
similar response rates between online and paper questionnaires [48]. A final limitation related
to the self-reported physical activity measure is that it is more accurate to say that we assessed
perceived intensity, as less fit individuals will feel exhausted by an intensity that a fit person will
feel comfortable.
Strengths of the current study include the large and heterogeneous sample, the use of well-
validated instruments, and the inclusion of several potential confounders.
Conclusions
The demonstrated health benefits of regular exercise suggest that facilitating young adults to
become more physically active should be a prioritized task both for political and educational
institutions.
Acknowledgments
We wish to thank all students participating in the study, as well as the three largest student
welfare organizations in Norway (SiO, Sammen, and SiT), who initiated and designed SHoT
study.
Author Contributions
Conceptualization: Børge Sivertsen.
Data curation: Kari Jussie Lønning, Børge Sivertsen.
Formal analysis: Michael Grasdalsmoen, Børge Sivertsen.
Funding acquisition: Kari Jussie Lønning, Børge Sivertsen.
Methodology: Michael Grasdalsmoen, Bo Engdahl, Mats K. Fjeld, Ólöf A. Steingrı́msdóttir,
Christopher S. Nielsen, Hege R. Eriksen, Børge Sivertsen.
Project administration: Kari Jussie Lønning.
Supervision: Børge Sivertsen.
Writing – original draft: Michael Grasdalsmoen, Børge Sivertsen.
Writing – review & editing: Bo Engdahl, Mats K. Fjeld, Ólöf A. Steingrı́msdóttir, Christopher
S. Nielsen, Hege R. Eriksen, Kari Jussie Lønning.
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