Does pain sensitivity correlate with gastrointestinal symptoms in runners? An observational survey study

Abstract

Objective:

Heightened pain sensitivity is common in functional gut disorders, but no research has examined whether it corresponds to exercise-associated gastrointestinal (GI) symptoms. We sought to explore whether scores on a questionnaire of pain sensitivity would correlate with GI symptoms during running.

Design:

This is a cross-sectional study.

Subjects:

The study involves 290 (137 male, 153 female) distance runners.

Methods:

Runners completed a survey inquiring about demographic, anthropometric and training information and rated GI symptoms at rest and during runs. In addition, the Pain Sensitivity Questionnaire (PSQ) was used to quantify pain sensitivity across all items (PSQ-Total) and on items typically rated as minor (PSQ-Minor). Spearman rho correlations were utilized to assess the associations between pain sensitivity and GI symptoms. Partial correlations were used to evaluate the associations after controlling for age, gender, running experience, body mass index and sleep problems.

Results:

PSQ scores weakly correlated with several GI symptoms at rest (rho = 0.13–0.20; p < 0.05), which remained largely intact in partial correlation analyses (partial rho = 0.12–0.18). PSQ scores weakly correlated with fullness, bloating and gas during runs (rho = 0.12–0.18; p < 0.05); fullness and bloating remained significant in the partial correlation analyses (partial rho = 0.12–0.15). These results were relatively consistent for both the PSQ-Total and PSQ-Minor.

Conclusions:

Although PSQ scores only weakly correlate with certain GI symptoms among runners, the effect sizes are similar to that of other predictors of GI distress. These results suggest a minor possible role of pain sensitivity in the development of certain GI symptoms in runners.

Introduction

Participation in endurance sport has increased over recent decades, particularly in events such as marathons, ultra-marathons and triathlons.^1–3 Endurance exercise induces numerous health and psychosocial benefits,^4,5 but there are also various forms of pain and discomfort that can reduce enjoyment of these activities. ⁶ One such factor is gastrointestinal (GI) distress, which is fairly prevalent during endurance exercise and can manifest as symptoms like nausea, vomiting, bloating, regurgitation/reflux, gas, cramping and urges to defecate. ⁷ While the severity and implications of these GI symptoms vary substantially, in some cases they can impair performance,^8,9 cause athletes to drop out of races,^9,10 and even result (albeit rarely) in severe medical consequences. ¹¹ The pathophysiology of exercise-associated GI distress is complex and not fully understood but likely involves a combination of circulatory, neuroendocrine and mechanical factors.^7,12 Regardless of the exact mechanisms, it is clear that intense, prolonged exercise can impair some aspects of GI function (e.g. intestinal barrier integrity, GI motility, esophageal sphincter tone) and ultimately induce GI symptoms.^7,12

An array of risk factors appears to influence the onset and/or severity of GI symptoms during endurance exercise. Athletes are more prone to these problems if they are younger, have less experience, are female, and have a history of GI distress.^7,13,14 Runners tend to experience higher rates of lower GI symptoms than cyclists, potentially due to the repetitive high-impact nature of the activity. ¹⁵ Furthermore, intakes of caffeine, fibre, fat, protein, large volumes of fluids and highly concentrated carbohydrate beverages have all been associated with GI distress in certain contexts.^7,13,16–18Other potential triggers include non-steroidal anti-inflammatory drugs (NSAIDs) ¹⁹ and psychological stress or anxiety.^20–22

While substantial evidence supports these risk factors in the development of exercise-associated GI symptoms, other areas require further exploration. One unexplored possibility is that an athlete’s sensitivity to pain may moderate the incidence and/or severity of such symptoms. Evidence to support this idea comes largely from populations with clinical gut disorders such as irritable bowel syndrome (IBS) and dyspepsia. For example, a common characteristic of IBS is visceral hypersensitivity (i.e. lower thresholds to painful or uncomfortable stimuli in the GI tract).^23,24 However, this sensitivity to painful or uncomfortable stimuli may also extend beyond the GI system. Piché et al. ²⁵ found that women with diarrhoea-predominant IBS not only had increased rectal sensitivity in comparison to healthy controls, but they also reported greater pain at the calf and forearm in response to contact thermode testing. Similarly, Stabell et al. ²⁶ showed that among people who reported symptoms consistent with IBS, tolerance to a cold-pressor test was diminished and heat-pain thresholds were lower in comparison to controls. Given that the cold-pressor and heat-pain tests were carried out using participants’ upper extremities, the researchers concluded that hyperalgesia is widespread in IBS and doesn’t solely affect the gut. ²⁶ Similar findings have been reported in studies of patients with IBS and functional gut disorders,^27,28 yet these types of findings are not unique to IBS. An investigation of Persian Gulf War veterans who developed GI symptoms during their tour of duty, for example, revealed they had higher levels of pain at the hands and feet in response to hot water application. ²⁹

The mechanisms responsible for possible concomitant GI and extraintestinal pain remain understudied but could include spinal sensitization or modulation of brain signalling. ³⁰ A study of IBS patients, for instance, found that intrarectal administration of lidocaine lessened not only rectal pain but also cutaneous pain in response to foot submersion in hot water, which suggests that both forms of pain are mediated by central sensitization mechanisms. ³¹ Furthermore, brain imaging research has revealed that visceral and extraintestinal (e.g. cutaneous) pain both correspond to the joint activation of several brain regions, such as the somatosensory cortex and posterior parietal cortex, which indicates commonalities in central pain processing. ³²

Taken together, the literature supports the notion that GI symptom severity is related to enhanced sensitivity to painful or uncomfortable sensations. However, this is yet to be assessed in athletic populations. Given that runners commonly experience GI symptoms, it would be useful to determine whether their symptoms are associated with pain sensitivity. As such, this study explored the associations between measures of subjective pain sensitivity and GI symptoms at rest and during exercise in trained runners. Our hypothesis was that pain sensitivity, assessed with the Pain Sensitivity Questionnaire (PSQ), would be positively correlated with GI symptoms at rest and during running. It should be noted that most correlation-based, observational studies that seek to identify predictors of GI symptoms during exercise typically only find small-to-moderate effect sizes (r or rho < 0.5) (e.g. Wilson^18,20), and this is likely because GI symptoms can be caused or exacerbated by many factors. In other words, any single factor is unlikely to explain a large proportion of the variance in GI symptoms experienced by athletes. Thus, we encourage readers to interpret the results of this study with that context in mind.

Methods

Participants

Runners were recruited by sending emails to contact persons for running clubs and endurance races with a description of the study and a link to an electronic, anonymous survey. The clubs and races contacted were diverse and included members and participants with wide ranges of running experiences and competition levels. Contact persons were asked to distribute the link. Social media (Twitter and Facebook) posts were also used to promote the study. To be eligible for inclusion, runners had to be at least 18 years of age and run at least 15 miles per week. Upon clicking the survey link, participants were asked to confirm that they met the inclusion criteria before proceeding to the remaining questions.

A total of 292 runners met the criteria and completed the survey. Two participants were dropped from the analyses due to missing data, resulting in 290 total runners (137 men, 153 women) being included in the analyses (Table 1). Most participants reported their race/ethnicity as non-Hispanic White (88.3%), while the remainder reported to be non-Hispanic Black (0.3%), non-Hispanic Asian (2.1%), Mexican American (1.7%), other Hispanic (1.7%), or other race/ethnicity (5.9%). Thirty-three (11.4%) runners reported having a GI condition.

Table 1.

Characteristics of the participants.

	All participants (n = 290)	Women (n = 153)	Men (n = 137)
Age (years)	44.0 (35.0–56.0)	40.0 (33.0–51.0)	50.0 ± (38.5–61.5)
BMI (kg/m2)	22.3 (20.6–24.6)	21.5 (20.2–23.4)	23.3 (21.8–25.8)
Running experience (years)	14.0 (7.0–28.0)	12.0 (6.0–20.0)	15.0 (8.0–33.5)
PSQ-Total (0–10)	2.9 (2.2–3.7)	2.8 (2.1–3.6)	3.2 (2.4–3.9)
PSQ-Minor (0–10)	1.9 (1.3–2.7)	1.9 (1.3–2.5)	2.0 (1.4–2.7)
SPI-I (0–100)	26.7 (16.7–40.0)	30.0 (20.0–43.3)	23.3 (16.7–35.0)
Total GI at rest (0–70)	6 (2–12)	7 (3–14)	5 (2–11)
Nausea (0–10)	0 (0–0)	0 (0–1)	0 (0–0)
Reflux/regurgitation (0–10)	0 (0–1)	0 (0–1)	0 (0–1)
Fullness (0–10)	0 (0–2)	0 (0–2)	0 (0–2)
Bloating (0–10)	1 (0–2)	2 (0–3)	0 (0–2)
Cramps (0–10)	0 (0–1)	0 (0–2)	0 (0–0)
Gas/flatulence (0–10)	2 (0–3)	2 (0–3)	2 (0–3)
Urge to defecate (0–10)	1 (0–3)	1 (0–3)	1 (0–3)
Total GI during runs (0–70)	5 (2–11)	5 (2–12)	5 (2–10)
Nausea (0–10)	0 (0–0)	0 (0–0)	0 (0–0)
Reflux/regurgitation (0–10)	0 (0–0)	0 (0–0)	0 (0–0)
Fullness (0–10)	0 (0–1)	0 (0–1)	0 (0–1)
Bloating (0–10)	0 (0–1)	0 (0–1)	0 (0–1)
Cramps (0–10)	0 (0–1)	0 (0–2)	0 (0–1)
Gas/flatulence (0–10)	1 (0–2)	1 (0–2)	1 (0–2)
Urge to defecate (0–10)	1 (0–4)	1 (0–4)	1 (0–4)

BMI: body mass index; GI: gastrointestinal; PSQ: Pain Sensitivity Questionnaire; SPI-I: Sleep Problems Index I.

Data presented as median (interquartile range).

Procedures

This study utilized a cross-sectional, observational design. An electronic anonymous survey was used for data collection, which included questions about participants’ demographics (age, race/ethnicity, gender), height, weight, running experience, typical GI symptoms at rest and while running, pain sensitivity and sleep habits. The presence of GI conditions was also inquired about but was not used to exclude participants due to the high prevalence of functional GI disorders (e.g. IBS, dyspepsia, constipation) in the general population. ³³ Body mass index (BMI) was calculated from height and weight.

Participants rated the typical severity of seven different GI symptoms at rest and during runs over the past month. Ratings from 0 (‘no discomfort’) to 10 (‘unbearable discomfort’) were possible, with 5 being ‘moderate discomfort’. This retrospective methodology has been previously validated. ³⁴ The following standardized definitions were used for each GI symptom:

• Nausea: A feeling of sickness in the stomach marked by an urge to vomit.

• Regurgitation/reflux: A sensation of food or fluid returning from the stomach to the oesophagus or mouth.

• Stomach fullness: A sensation of fullness or abdominal pressure in the upper abdomen.

• Bloating: A feeling of distension from a build-up of gas in the gut.

• Abdominal cramps: Pain or cramping sensation, often experienced in the mid- or lower portion of the abdomen.

• Gas/flatulence: Gas or flatus expelled through the anus.

• Urge to defecate: Sensation of needing to pass a bowel movement.

Total GI-symptom burdens at rest and during runs were quantified by summing ratings across all symptoms. Given that symptoms can have different causes and consequences for runners, ratings for each independent symptom were analysed as well.

Pain sensitivity was evaluated with the valid and reliable PSQ. ³⁵ The PSQ asks participants to imagine that they are in a series of daily life situations, decide whether the situation would be painful, and rate the pain from 0 to 10. An example situation includes: ‘imagine you pick up a hot pot by inadvertently grabbing its equally hot handles’. Pain severity is rated on a scale from 1 ( ‘just noticeable pain’) to 10 ( ‘most severe pain imaginable’), while a rating of 0 is given if the participant imagines they would not experience pain. Fourteen items involve situations that are expected to be rated as painful for most participants. The remaining three items include situations that are normally not considered painful. These three items are interspersed throughout the PSQ to serve as non-painful reference items. The mean across all items (PSQ-Total) and the mean across items representing situations that typically elicit ‘minor pain’ (PSQ-Minor) were calculated. PSQ-Minor was included in this analysis because it was previously found to have the largest associations with laboratory-based pain threshold and intensity tests, ³⁵ and it may also be appropriate for detecting associations with exercise-induced GI distress, considering that most symptoms tend to be mild-moderate. ⁷

The final portion of the survey included the Medical Outcomes Study (MOS) Sleep Scale, a valid and reliable assessment of general sleep habits. ³⁶ Responses from six items were used to calculate the Sleep Problems Index (SPI)-I, which provides a summary of sleep problems. Sleep problems are known to impact pain sensations ³⁷ and were therefore important to assess as a potential confounding variable.

Statistical analysis

Data were analysed using SPSS version 26 (IBM, Armonk, NY, USA). The distribution of the data was assessed with the Shapiro–Wilk test and visual inspection of histograms. Non-parametric analyses were used because all GI-symptom and PSQ data exhibited non-normal distributions. Furthermore, previous articles on predictors and correlates of GI distress during exercise have utilized non-parametric approaches.^18,20,38 As such, descriptive data are reported as medians and interquartile ranges.

Spearman’s rho correlations were used to evaluate the association between measures of pain sensitivity (PSQ-Total, PSQ-Minor) and measures of GI symptoms (total GI as well as individual symptom severity) at rest and during runs. Partial Spearman’s rho correlations were then used to evaluate the associations after controlling for age, gender, years of running experience, SPI-I and BMI. These variables were chosen as potential confounders because recent studies have identified them as being significant correlates to GI symptoms ¹⁸ and because they are commonly controlled for in similar studies on risk factors for GI symptoms in endurance athletes. ²¹ A two-sided p value of < 0.05 was used as the threshold for statistical significance.

Results

Table 1 displays an overview of participants’ demographics, PSQ scores, SPI-I scores and GI symptoms. Overall, major GI distress was relatively sparse in this sample, with median ratings ⩽ 7 out of 70 for total GI symptoms at rest and during runs. Each individual symptom had a median rating ⩽ 2, though a wide range of responses were provided across all participants (Table 1).

The correlations of age, BMI, running experience and SPI-I with GI symptoms are shown in Table 2. Age had significant negative associations with ratings of nausea, fullness, bloating, cramps, gas/flatulence and total GI symptom scores at rest (rho = −0.15 to −0.23; p < 0.05), and with nausea, reflux/regurgitation, cramps and total GI symptom scores during runs (rho = −0.14 to −0.25; p < 0.05). Similarly, running experience was inversely associated with nausea, bloating, cramps and total GI symptom scores at rest (rho = −0.12 to −0.17; p < 0.05). SPI-I scores were significantly associated with all GI symptoms at rest (rho = 0.16 to 0.30; p < 0.05) and during runs (rho = 0.14 to 0.23; p < 0.05). BMI was not significantly associated with any GI symptom other than reflux/regurgitation at rest (rho = 0.14; p = 0.014).

Table 2.

Correlations of demographic, training and sleep variables with GI symptoms.

	Age	BMI	Running experience	SPI-I
At rest
Total GI	–0.21 (.00)*	0.01 (.90)	–0.13 (.03)*	0.30 (.00)*
Nausea	–0.16 (.01)*	0.01 (.83)	–0.17 (.00)*	0.16 (.01)*
Reflux/regurgitation	–0.05 (.43)	0.14 (.01)*	–0.07 (.22)	0.21 (.00)*
Fullness	–0.19 (.00)*	0.01 (.88)	–0.10 (.10)	0.17 (.00)*
Bloating	–0.23 (.00)*	–0.07 (.26)	–0.13 (.03)*	0.21 (.00)*
Cramps	–0.19 (.00)*	0.05 (.43)	–0.12 (.03)*	0.24 (.00)*
Gas/flatulence	–0.15 (.01)*	–0.03 (.66)	–0.04 (.51)	0.26 (.00)*
Urge to defecate	0.01 (.92)	0.09 (.13)	0.06 (.31)	0.16 (.01)*
During runs
Total GI	–0.20 (.00)*	0.03 (.65)	–0.06 (.30)	0.23 (.00)*
Nausea	–0.14 (.02)*	–0.04 (.46)	–0.12 (.05)	0.14 (.02)*
Reflux/regurgitation	–0.16 (.01)*	0.01 (.82)	–0.11 (.06)	0.19 (.00)*
Fullness	–0.08 (.20)	0.06 (.33)	–0.03 (.60)	0.20 (.00)*
Bloating	–0.11 (.05)	0.02 (.69)	–0.08 (.19)	0.21 (.00)*
Cramps	–0.25 (.00)*	–0.04 (.54)	–0.10 (.09)	0.17 (.00)*
Gas/flatulence	–0.09 (.12)	0.01 (.84)	0.00 (.99)	0.14 (.02)*
Urge to defecate	–0.07 (.23)	0.06 (.28)	0.02 (.69)	0.17 (.01)*

BMI: body mass index; GI: gastrointestinal; SPI-I: Sleep Problems Index I.

Values of p are displayed in parentheses. Total GI is the sum of ratings across all symptoms.

^*Significant at p < 0.05.

The correlations and partial correlations between PSQ measures and GI symptoms at rest are displayed in Table 3. PSQ-Total had significant positive correlations with ratings of reflux/regurgitation, gas/flatulence, urge to defecate and total GI symptom scores (rho = 0.13 to 0.20; p < 0.05). After adjusting for control variables, PSQ-Total was significantly correlated with bloating, gas/flatulence and total GI symptom scores (partial rho = 0.12 to 0.18; p ⩽ 0.04). PSQ-Minor scores significantly correlated with reflux/regurgitation, gas/flatulence, urge to defecate and total GI symptom scores (rho = 0.13 to 0.17; p ⩽ 0.02). The correlations with gas/flatulence, urge to defecate and total GI symptom scores remained significant after adjustment for the control variables (partial rho = 0.13 to 0.16; p ⩽ 0.03).

Table 3.

Correlations between pain sensitivity measures and GI symptoms at rest.

	PSQ-Total		PSQ-Minor
	Correlation	Partial correlation	Correlation	Partial correlation
Nausea	0.04 (.56)	0.05 (.43)	0.09 (.14)	0.09 (.13)
Reflux/regurgitation	0.13 (.03)*	0.10 (.11)	0.13 (.02)*	0.10 (.09)
Fullness	0.08 (.17)	0.08 (.20)	0.10 (.09)	0.09 (.13)
Bloating	0.09 (.12)	0.12 (.04)*	0.10 (.10)	0.11 (.07)
Cramps	0.04 (.45)	0.05 (.37)	0.05 (.39)	0.04 (.49)
Gas/flatulence	0.20 (.00)*	0.18 (.00)*	0.15 (.01)*	0.13 (.03)*
Urge to defecate	0.15 (.01)*	0.12 (.05)	0.17 (.00)*	0.14 (.02)*
Total GI at rest	0.18 (.00)*	0.18 (.00)*	0.17 (.00)*	0.16 (.01)*

GI: gastrointestinal; PSQ: Pain Sensitivity Questionnaire.

Values of p are displayed in parentheses. Partial correlations are the correlation coefficients after controlling for age, gender, body mass index, years of running experience and Sleep Problems Index I scores.

^*Significant at p < 0.05.

The correlations and partial correlations between pain sensitivity measures and GI symptoms during runs are shown in Table 4. PSQ-Total had significant correlations with fullness, bloating and gas/flatulence (rho = 0.12 to 0.13; p ⩽ 0.04). Only the correlation with bloating remained significant after adjusting for control variables (partial rho = 0.12; p = 0.04). Similarly, PSQ-Minor had significant correlations with fullness, bloating, gas/flatulence and total GI symptom scores (rho = 0.12 to 0.18; p ⩽ 0.04). The correlations with fullness and bloating, but not gas/flatulence or total GI symptom scores, remained significant after adjustment (partial rho = 0.13 to 0.15; p ⩽ 0.03).

Table 4.

Correlations between pain sensitivity measures and GI symptoms during runs.

	PSQ-Total		PSQ-Minor
	Correlation	Partial correlation	Correlation	Partial correlation
Nausea	–0.04 (.46)	–0.05 (.45)	0.00 (.98)	0.00 (.93)
Reflux/regurgitation	0.09 (.14)	0.07 (.23)	0.10 (.09)	0.09 (.15)
Fullness	0.12 (.04)*	0.10 (.10)	0.18 (.00)*	0.15 (.01)*
Bloating	0.13 (.03)*	0.12 (.04)*	0.14 (.02)*	0.13 (.03)*
Cramps	–0.04 (.50)	–0.03 (.61)	–0.03 (.60)	–0.03 (.57)
Gas/flatulence	0.13 (.03)*	0.12 (.05)	0.12 (.04)*	0.11 (.07)
Urge to defecate	0.02 (.69)	0.00 (.97)	0.07 (.25)	0.04 (.46)
Total GI during runs	0.09 (.11)	0.09 (.15)	0.12 (.04)*	0.11 (.07)

GI: gastrointestinal; PSQ: Pain Sensitivity Questionnaire.

Values of p are displayed in parentheses. Partial correlations are the correlation coefficients after controlling for age, gender, body mass index, years of running experience and Sleep Problems Index I scores.

^*Significant at p < 0.05.

Discussion

The goal of this study was to assess the associations between measures of pain sensitivity (PSQ-Total and PSQ-Minor) and GI symptoms in runners. Many different triggers for GI disturbances have been identified in previous literature, with most studies focusing on pharmacological, nutritional, environmental and mechanical contributors.^7,12 While unexplored in athletic populations, research has documented that hypersensitivity to painful stimuli is more prevalent in IBS and other functional GI conditions than in healthy populations.^25–29 It is perhaps unsurprising that visceral hypersensitivity is common in these gut disorders, but the literature also points to a more generalized, widespread hypersensitivity to pain as well. The widespread hyperalgesia observed in some studies of IBS patients may be attributable to altered pain processing, increased tendency to report pain and/or comorbid psychological distress.^25,26,39 Based on these observations, we hypothesized that the severity of GI symptoms would be associated with pain sensitivity in distance runners. Overall, measures of pain sensitivity (PSQ-Total and PSQ-Minor) had significant, albeit relatively weak, positive correlations with several of the GI symptom ratings at rest and during runs (nausea was a clear exception). After adjusting for age, gender, running experience, BMI and SPI-I scores, the correlations with these GI symptoms remained very similar (the partial rho effect sizes were no more than 0.03 different than the unadjusted rho effect sizes).

There are several potential reasons for the relatively small associations between GI symptoms and PSQ measures. Pain sensitivity is a complex and multi-dimensional phenomenon, and experimentally evaluated pain sensitivity can vary based on the body location that is investigated, the specific pain stimulus used and the timing of the evaluation. ⁴⁰ The PSQ is thought to represent average sensitivity across different pain modalities, locations and time points, representing a construct of ‘general pain sensitivity’. ³⁵ Ruscheweyh et al. ³⁵ found that PSQ-total and PSQ-minor scores had moderate-to-large correlations (r = 0.56–0.64) with pain intensity ratings reported across a battery of experimental pain tests, although other studies have found weaker associations with pain intensity and tolerance from experimental stimuli (e.g. r < 0.4). ⁴¹ In general, scores on the PSQ tend to correlate more strongly with pain intensity than pain thresholds.^35,41 While IBS patients may experience symptoms due to a widespread hypersensitivity to painful or uncomfortable stimuli,^25,26 it is possible that the construct of pain sensitivity evaluated with the PSQ is not as relevant to exercise-induced GI symptoms.

Another plausible explanation for the relatively weak associations is the fact that other well-established contributors to GI distress typically have small-to-modest correlations with GI symptoms in endurance athletes as well. For example, Wilson ¹⁸ found modest-sized, statistically significant associations between GI symptoms and the intakes of caffeine (rho = 0.30) and energy (rho = 0.28) on the morning of a triathlon. Similar sized correlations with exercise-associated GI symptoms have been found for stress and anxiety, ²⁰ history of GI symptoms, ³⁸ sleep habits, ⁴² average run intensity ²⁰ and macronutrient intake during marathoning. ⁴³ Any individual trigger is unlikely to account for a large proportion of the variance in GI symptoms, as each symptom can have multiple and independent causes. That being said, an unfavourable combination of risk factors could result in a higher risk of symptoms over time. ⁷ Thus, even the small correlations noted in this study could be meaningful if a runner has high pain sensitivity in combination with several other risk factors for GI distress.

The median PSQ scores in this study were slightly lower than values observed in healthy controls from other studies (e.g. Ruscheweyh et al. ³⁵ ), which is not surprising considering that the sample consisted of distance runners who choose to engage in an activity involving physical discomfort. Indeed, several articles have shown that athletes have higher pain tolerance compared with non-athlete controls, ⁴⁴ particularly those who are from sports involving long durations of physical exertion such as triathletes and distance runners.^45,46 Furthermore, GI symptoms were mostly mild in severity (Table 1). The combination of these factors may be another reason for the relatively weak correlations observed in this analysis. In the future, it may be useful to evaluate GI symptoms prospectively, rather than asking runners to retrospectively rate their ‘typical’ symptoms. While a runner may not experience moderate-severe GI distress on a typical day of training, it is likely that they will experience at least one moderate-severe symptom over the course of several weeks. For example, Wilson ²⁰ had runners track GI symptoms during runs over a 30-day period and found that they experienced a GI symptom ⩾ 3 out 10 on nearly half (45.6%) of their runs.

A recent study by Wilson ⁴² found that scores on the SPI-I were modestly correlated (rho = 0.26) with upper GI symptoms during endurance races. Given that sleep disruptions have been shown to exacerbate pain ratings in several contexts, ³⁷ we felt it was prudent to include the SPI-I as a control variable. In congruence with Wilson, ⁴² the current study found that SPI-I had significant positive correlations with total GI-symptom burden (rho = 0.23) as well as with individual GI symptoms during runs (rho = 0.14 to 0.21). However, the inclusion of SPI-I scores in the partial correlation analyses, along with several other control variables, had little-to-no impact on the size of the correlations between pain sensitivity and GI symptoms. This suggests that the associations between pain sensitivity and GI symptoms may function independently of sleep problems among runners.

There are several strengths to this study. The evaluation of potential confounders (age, BMI, gender, running experience, SPI-I) allowed the use of partial correlations in addition to unadjusted Spearman’s rho correlations. The sample size was large and included relatively equal numbers of men and women, which is often not the case in sport science research. Still, there are several limitations, including that this study used an observational design that cannot establish cause and effect. As such, a cautious interpretation of the findings should be taken given that reverse causality is possible. In addition, the evaluation of GI symptoms was retrospective rather than prospective. This was done to reduce the burden on participants and increase the sample size for this novel analysis. Given the somewhat exploratory nature of this investigation, we did not correct for multiple correlations, and therefore our analysis may be more prone to type I error. We also acknowledge that the relatively low variation in PSQ scores and GI-symptom ratings may have contributed to the small correlations. Finally, there are several other confounding variables that would ideally be evaluated and adjusted for, including nutritional intake, NSAID use, and psychological factors (stress and anxiety). Their exclusion from this study was again to reduce the burden on participants. Future studies should consider collecting data prospectively and evaluating additional covariates to further elucidate the association between pain sensitivity and GI distress in runners.

Conclusion

This was the first investigation to evaluate the correlations between subjective pain sensitivity and GI symptoms in runners. After controlling for several potential confounders, pain sensitivity measures were weakly correlated (adjusted rho = 0.12 to 0.18) with several GI symptoms at rest and during runs over the previous month. Overall, the results imply that pain sensitivity could play a modest role in the development of some GI symptoms in runners. Given that pain sensitivity and reported GI symptoms were relatively low in this study, future studies may consider recruiting individuals who report higher levels of pain sensitivity or GI distress during exercise (e.g. during ultra-running). Furthermore, data could be collected prospectively rather than retrospectively, objective measures of pain sensitivity could be evaluated and other covariates (e.g. psychological variables, nutritional intake) could be considered.