European Journal of Pain. 2016 Jul; 20(6): 967-976. doi: 10.1002/ejp.821
Lean mass predicts conditioned pain modulation in adolescents across weight status.
Stolzman S. – Program in Exercise Physiology, Department of Health & Human Performance, Concordia University Wisconsin, Mequon, WI.
Hoeger Bement M. – Department of Physical Therapy, Marquette University, Milwaukee, WI
BACKGROUND: There is a wide continuum of conditioned pain modulation (CPM) in adults with older adults experiencing an attenuated CPM response compared with younger adults. Less is known for adolescents and the role of anthropometrics.
METHODS: Fifty-six adolescents (15.1 ± 1.8 years; 32 normal weight and 24 overweight/obese; 27 boys) completed in a CPM session that included anthropometric testing. Pressure pain thresholds were measured at the nailbed and deltoid muscle (test stimuli) with the foot submerged in a cool or ice water bath (conditioning stimulus). Weight status, body composition (Dual-energy X-ray absorptiometry scan), physical activity levels and clinical pain were also evaluated.
RESULTS: The CPM response in adolescents was similar across sites (nailbed vs. deltoid), weight status (normal vs. overweight/obese) and sex. CPM measured at the deltoid muscle was positively associated with left arm lean mass but not fat mass; lean mass of the arm uniquely predicted 10% of the CPM magnitude. CPM measured at the nailbed was positively correlated with physical activity levels.
CONCLUSIONS: These results suggest that lean mass and physical activity levels may contribute to endogenous pain inhibition in adolescents across weight status.
Individuals who are overweight or obese are more likely to report pain than individuals with normal weigh, and as weight status increases (overweight to class III obesity), reports of pain also increase. The reasons for this positive relation between weight status and pain are not clear. Potential contributing factors for the increase in pain include weight related increases in mechanical stress, chronic low grade inflammation, psychological factors, low fitness levels, and abnormal endogenous pain modulation.
One measurement of endogenous pain modulation is conditioned pain modulation (CPM), which is the concept that ‘pain inhibits pain.’ In other words, when we perceive pain our bodies have an amazing ability to inhibit subsequent pain by activating descending inhibitory pain pathways. Little research has been done regarding the impact of weight status on CPM; however there is quite a bit of research showing that people with chronic pain have abnormal endogenous pain modulation including less efficient CPM. Therefore, we hypothesized that overweight/obese adolescents would report more pain and have attenuated CPM compared with normal weight adolescents.
To our surprise, CPM and clinical pain reports were similar between the weight groups. Earlier studies that showed the high prevalence of pain in overweight/obese adolescents were in a clinical setting,1 whereas our population was a community-based sample with the majority of the adolescents categorized as physically fit.2 Physical fitness is an important contributor to weight status and endogenous pain modulation.3,4 Thus, the negligible pain reports by the adolescents combined with the high physical fitness levels likely explains why the adolescents had similar CPM across weight groups. Thus, this adolescent population may not represent the clinical population of adolescents with overweight/obesity and co-morbidities; however, this adolescent population may be more representative of a community population who is still overweight/obese but also physically fit active and therefore, not as medically intense. These results demonstrate the importance of a comprehensive approach, including assessment of physical activity participation and physical fitness levels, when evaluating the impact of weight status on health.
In this study, we used Dual-energy X-ray absorptiometry (DXA) scans to measure body composition (Figure 1). Body composition analysis gives us more detailed information than more traditional measures of weight status, such as body mass index (BMI), about the total amount of fat on the body and specifically where it is located. Because of the relation between increasing weight status and pain, we were mainly interested on the impact of body fat on endogenous pain modulation (e.g., CPM). The CPM protocol involved measuring pressure pain thresholds with and without another noxious conditioning stimulus (Figure 2); pressure pain thresholds were measured while the adolescent placed his/her foot in a neutral non-painful water bath and again with the foot submerged in a painful ice water bath. Pressure pain should be less (i.e., increase in pain thresholds) with the application of the painful conditioning stimulus (i.e., pain inhibits pain) than without the conditioning stimulus. Pain thresholds were measured at two sites (nailbed and deltoid muscle) that varied in body fat distribution. For both sites, CPM was similar between the normal weight and overweight/obese adolescents. In other words, increased weight status does not preclude overweight/obese adolescents from experiencing endogenous pain inhibition.
Figure 1 – Dual-energy X-ray absorptiometry (DEXA) Scan for body composition analysis
What we did not expect was that CPM measured at the deltoid muscle would be associated with left arm lean mass but not fat mass. In hindsight, this makes sense given the importance of physical activity in endogenous pain modulation. Thus, increasing physical activity and lean mass provides insight into how exercise can provide pain relief through more efficient endogenous pain modulation.2
Previously we have shown an association between pain relief following exercise (exercise-induced hypoalgesia [EIH]) and lean mass in this same adolescent population.2 Interestingly, the exercise-induced pain relief was also related to sedentary behavior; adolescents with greater sedentary behavior reported less pain relief following maximal treadmill running. From the clinical standpoint, health care professionals often encourage physical activity, and our research emphasizes the importance of decreasing sedentary behaviors to optimize pain relief with exercise (EIH). In today’s health care system, exercise is an excellent nonpharmacological approach for pain relief.
Overall, this study reinforces the importance of regular physical activity and the potential benefits related to pain management potentially by increasing lean mass. From a weight management standpoint, these results highlight the importance of a multi-focus approach that does not solely focus on weight loss. Increasing lean mass is crucial for improving strength and aerobic capacity; both of which contribute to improved physical fitness. Previously we have shown that physical fitness impacted quality of life reports more than weight status.2 Thus, the health benefits of increasing physical activity to improve overall physical fitness are extensive and may occur independent of weight loss.
Future exercise training studies with a focus on increasing lean mass are warranted and should incorporate adolescents across the weight status from both clinical and community populations. In addition, while this study demonstrated a relation between CPM and lean mass, future training studies should incorporate more comprehensive assessments of endogenous pain modulation.
Figure 2 – Conditioned pain modulation protocol set-up
1. Hainsworth KR, Miller LA, Stolzman SC, et al. Pain as a comorbidity of pediatric obesity. ICAN. 2012;4(5):315-320.
2. Stolzman S, Danduran M, Hunter SK, Bement MH. Pain response after maximal aerobic exercise in adolescents across weight status. Med Sci Sports Exerc. 2015;47(11):2431-2431-40.
3. Naugle KM, Riley JL,3rd. Self-reported physical activity predicts pain inhibitory and facilitatory function. Med Sci Sports Exerc. 2014;46(3):622-629.
4. Waleh MQ. Impacts of physical activity on the obese. Prim Care. 2016;43(1):97-107, ix.
• Foundation for Physical Therapy — Promotion of Doctoral Studies (PODS) I Scholarship (SS)
• Foundation for Physical Therapy – Promotion of Doctoral Studies (PODS) II Scholarship (SS)
• American Association of University Women – Dissertation Fellowship (SS)
• Marquette University President’s Council — Raynor Fellowship (SS)
• National Center for Advancing Translational Sciences, National Institutes of Health, through Grant Number 8UL1TR000055 (SS & MHB)
Stacy C Stolzman, PhD, MPT
Assistant Professor & Pediatric Physical Therapist
Department of Health & Human Performance
Program in Exercise Physiology
College of Arts & Sciences
Concordia University Wisconsin
12800 N Lake Shore Drive
Mequon, WI 53097