Conditioned pain modulation among young, healthy, and physically active African American and non-Hispanic White adults

https://doi.org/10.1016/j.jpsychores.2017.05.012Get rights and content

Highlights

  • African Americans (AAs) show reduced efficiency of pain modulation compared to non-Hispanic Whites (NHWs).

  • Physical activity (PA) may help improve efficiency of pain modulation.

  • We compared pain modulation and PA in AAs and NHWs.

  • AAs and NHWs show similar pain modulation and PA levels.

  • PA may help attenuate the difference in pain modulation between AAs and NHWs.

Abstract

Objective

Research shows that African American (AA) adults experience more severe and frequent pain compared to non-Hispanic White (NHW) adults. Additionally, experimental studies demonstrate that AA adults exhibit less efficient central pain inhibition compared to NHW adults, which may partially explain the racial/ethnic disparities in pain. Evidence suggests that regular physical activity (PA) may help improve central pain inhibition, but research shows that AA adults engage in less PA, and are less likely to meet PA guidelines for health promotion compared to NHW adults. These observations suggest that PA levels may help better understand the racial/ethnic difference in central pain inhibition. Therefore, this study compared central pain inhibition and PA levels among AA and NHW adults.

Methods

Young and healthy participants were recruited on campus, and 27 AA and 27 NHW adults completed this study. Central pain inhibitory processing was assessed using conditioned pain modulation (CPM), where changes in electrical pain ratings were quantified during and after exposure to pressure pain compared to baseline. PA levels were assessed using self-report questionnaires and accelerometer.

Results

The participants were generally physically active, and most participants in both groups met the public recommendation of PA for health promotion. Electrical pain ratings were significantly reduced during and after exposure to pressure pain compared to baseline. There was no racial/ethnic difference in a magnitude of changes in electrical pain ratings.

Conclusion

Young, healthy, and physically active AA and NHW adults exhibit similar CPM responses. Regular PA may help attenuate the racial/ethnic difference in CPM responses.

Introduction

The literature documents that African American (AA) adults suffer from a greater intensity of pain, and experience pain conditions more often compared to non-Hispanic White (NHW) adults in a variety of clinical conditions, including postoperative pain, arthritis, cancer pain, and angina [1], [2], [3], [4]. Although mechanisms underlying the racial/ethnic disparities in clinical pain experience are currently unknown, evidence from experimental studies shows that African American (AA) adults are generally more sensitive to experimental pain stimuli, characterized by reduced pain thresholds and tolerances, as well as increased pain ratings, when compared to non-Hispanic White (NHW) adults [1], [2], [5], [6], [7]. Furthermore, physiological thresholds of nociceptive flexion reflex in response to noxious stimuli are found to be lower in AA adults compared to NHW adults [8]. These findings collectively suggest that AA adults exhibit an increased sensitivity to pain compared to NHW adults.

It has been suggested that pain sensitivity may be determined by the complex interactions of endogenous pain modulatory mechanisms that can either inhibit or facilitate nociceptive transmission [9]. Therefore, it is possible that the observed racial/ethnic difference in pain sensitivity may reflect a difference in efficiency of endogenous pain modulation between AA and NHW adults. A laboratory pain test that has been used frequently to investigate central pain inhibitory processing has been termed as conditioned pain modulation (CPM). The CPM is typically characterized by reduced sensitivity to pain stimulus applied to one part of body during and immediately after concurrent application of the other pain stimulus applied to a distant part of body [10], [11]. Using the CPM paradigm, one study demonstrated that AA adults exhibit smaller CPM responses compared to NHW adults [12], suggesting the presence of racial/ethnic difference in efficiency of central pain inhibition, which may potentially explain the documented racial/ethnic difference in clinical pain experience [1].

Currently, our understanding on the underlying mechanisms of CPM responses is still limited; however, past research generally demonstrates that a neurophysiological interaction exists between pain and cardiovascular regulatory systems [13], [14]. For example, ample evidence from experimental studies indicates that there is an inverse association between blood pressure and pain sensitivity [15], [16], and it has been hypothesized that this blood pressure-related hypoalgesia may reflect a function of descending pain modulation that is initiated by increased neural input from baroreceptor that occurs in response to elevation of blood pressure. It was shown, however, that AA adults report a greater intensity of muscle pain during exercise compared to NHW adults, albeit a similar magnitude of blood pressure elevation during exercise, suggesting a potential impairment in the descending pain modulatory processing linked to cardiovascular regulatory system among AA adults [7]. The role of blood pressure in CPM responses is still poorly understood, but there is preliminary evidence that blood pressure elevation plays a role in augmenting CPM responses [17], [18].

There is growing evidence in the literature suggesting that regular engagement in physical activity (PA) may influence pain sensitivity [19], [20], [21], [22] and CPM responses [23], [24], [25], [26], such that physically active individuals exhibit lower sensitivity to pain stimuli and greater CPM responses compared to less active individuals. Benefits of regular PA on general health promotion are well accepted, and a PA guideline has been published to help promote general health among the public (e.g., 150 min or more of aerobic nature of moderate intensity PA per week) [27]. It has been shown that those who are active enough to meet the PA guideline exhibit reduced pain sensitivity compared to those who are insufficiently active [20]. Furthermore, a recent study reports that those who engage in the publicly recommended amount of PA exhibit greater CPM responses compared to less active adults [24], suggesting that regular PA at the recommended levels may help improve central pain inhibitory processing. In addition to regular engagement in PA, it has been well-documented that acute exercise also influences pain sensitivity, such that individuals typically experience systemic reductions in pain sensitivity during and after a single bout of exercise, a phenomenon termed as exercise-induced hypoalgesia [28], [29]. Interestingly, one study showed that AA adults exhibit smaller exercise-induced hypoalgesia responses compared to NHW adults [6], adding to the database regarding potential impairment of central pain inhibitory processing among AA adults. It is well known that benefits of regular PA extend into psychological health as well, and past research shows an inverse association between regular PA and pain catastrophizing [30], a psychological factor that is known to influence pain sensitivity. Pain catastrophizing generally describes one's negative thoughts and feelings associated with pain experiences, and there is some evidence that CPM responses are inversely associated with the degree of pain catastrophizing [31], [32]. However, the involvement of pain catastrophizing in CPM responses in AA and NHW adults is still unclear.

Despite such beneficial effects of regular PA on pain sensitivity and CPM responses, epidemiological studies generally shows that AA adults are less physically active [33], [34], [35], and are less likely to be active enough to meet similar PA guidelines when compared to NHW adults [36], [37], [38]. These observations potentially lead to a hypothesis that reduced CPM responses among AA adults may be explained by their reduced PA levels compared to NHW adults. However, no study has been published thus far examining the influence of PA levels on racial/ethnic difference in CPM responses between AA and NHW adults. Therefore, this study compared CPM responses and PA levels using both subjective and objective assessment of PA in AA and NHW adults to examine the potential influence of their PA on CPM responses. Based on the past research, we hypothesized that AA adults would show reduced PA levels and CPM responses compared to NHW adults.

Section snippets

Participants

A total of 54 healthy AA and NHW adults participated in this study (13 AA men, 13 NHW men, 14 AA women, & 14 NHW women). The participants were recruited at a large state university located in south region of the United States of America, where student body traditionally consists of racially diverse populations. A brief study advertisement was incorporated into a weekly campus newsletter, and the newsletter was circulated to students and university staff via a campus-wide electronic mailing

Participants' characteristics

A total of 27 AA and 27 NHW adults completed this study, with an interval between the two sessions ranging from 8 to 18 days. Results for the participants' characteristics indicated that there were no significant racial/ethnic differences in BMI, resting SBP, resting DBP, and resting HR (F1, 52 = 0.079–2.371, ps > 0.05). However, the results indicated a significant racial/ethnic difference in age (F1, 52 = 4.971, p = 0.030), showing that NHW adults were older than AA adults. Results for the PCS data

Discussion

The purpose of the present study was to examine the potential role of PA in the relationship between race/ethnicity and central pain inhibitory processing as quantified by CPM. The results indicated that CPM responses were comparable in young and healthy AA and NHW adults who were recruited on campus. The results also indicated that most participants were physically active enough to meet the public recommendation of PA, and the percentage of those who met the publicly recommended amount of PA

Conflict of interest

There is no conflict of interest among the authors.

Acknowledgement

We thank Ramona Harwell for her administrative support for this study.

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