Kelly M. Naugle

A Meta-Analytic Review of the Hypoalgesic Effects of Exercise

UNLABELLED The purpose of this article was to examine the effects of acute exercise on pain perception in healthy adults and adults with chronic pain using meta-analytic techniques. Specifically, studies using a repeated measures design to examine the effect of acute isometric, aerobic, or dynamic resistance exercise on pain threshold and pain intensity measures were included in this meta-analysis. The results suggest that all 3 types of exercise reduce perception of experimentally induced pain in healthy participants, with effects ranging from small to large depending on pain induction method and exercise protocol. In healthy participants, the mean effect size for aerobic exercise was moderate (d(thr) = .41, d(int) = .59), while the mean effect sizes for isometric exercise (d(thr) = 1.02, d(int) = .72) and dynamic resistance exercise (d(thr) = .83, d(int) = .75) were large. In chronic pain populations, the magnitude and direction of the effect sizes were highly variable for aerobic and isometric exercise and appeared to depend on the chronic pain condition being studied as well as the intensity of the exercise. While trends could be identified, the optimal dose of exercise that is needed to produce hypoalgesia could not be systematically determined with the amount of data available. PERSPECTIVE This article presents a quantitative review of the exercise-induced hypoalgesia literature. This review raises several important questions that need to be addressed while also demonstrating that acute exercise has a hypoalgesic effect on experimentally induced pain in healthy adults, and both a hypoalgesic and hyperalgesic effect in adults with chronic pain.

Self-reported Physical Activity Predicts Pain Inhibitory and Facilitatory Function.

UNLABELLED Considerable evidence suggests regular physical activity can reduce chronic pain symptoms. The dysfunction of endogenous facilitatory and inhibitory systems has been implicated in multiple chronic pain conditions. However, few studies have investigated the relationship between levels of physical activity and descending pain modulatory function. PURPOSE The purpose of this study was to determine whether self-reported levels of physical activity in healthy adults predicted 1) pain sensitivity to heat and cold stimuli, 2) pain facilitatory function as tested by temporal summation (TS) of pain, and 3) pain inhibitory function as tested by conditioned pain modulation (CPM) and offset analgesia. METHODS Forty-eight healthy adults (age range = 18-76 yr) completed the International Physical Activity Questionnaire (IPAQ) and the following pain tests: heat pain thresholds, heat pain suprathresholds, cold pressor pain, TS of heat pain, CPM, and offset analgesia. The IPAQ measured levels of walking, moderate, vigorous, and total physical activity over the past 7 d. Hierarchical linear regressions were conducted to determine the relationship between each pain test and self-reported levels of physical activity while controlling for age, sex, and psychological variables. RESULTS Self-reported total and vigorous physical activity predicted TS and CPM (P < 0.05). Individuals who self-reported more vigorous and total physical activity exhibited reduced TS of pain and greater CPM. The IPAQ measures did not predict any of the other pain measures. CONCLUSIONS These results suggest that healthy older and younger adults who self-report greater levels of vigorous and total physical activity exhibit enhanced descending pain modulatory function. Improved descending pain modulation may be a mechanism through which exercise reduces or prevents chronic pain symptoms.

Obesity and diabetes as accelerators of functional decline: can lifestyle interventions maintain functional status in high risk older adults?

Obesity and diabetes are known risk factors for the development of physical disability among older adults. With the number of seniors with these conditions rising worldwide, the prevention and treatment of physical disability in these persons have become a major public health challenge. Sarcopenia, the progressive loss of muscle mass and strength, has been identified as a common pathway associated with the initial onset and progression of physical disability among older adults. A growing body of evidence suggests that metabolic dysregulation associated with obesity and diabetes accelerates the progression of sarcopenia, and subsequently functional decline in older adults. The focus of this brief review is on the contributions of obesity and diabetes in accelerating sarcopenia and functional decline among older adults. We also briefly discuss the underexplored interaction between obesity and diabetes that may further accelerate sarcopenia and place obese older adults with diabetes at particularly high risk of disability. Finally, we review findings from studies that have specifically tested the efficacy of lifestyle-based interventions in maintaining the functional status of older persons with obesity and/or diabetes.

Spatiotemporal variability during gait initiation in Parkinson's disease

During gait initiation (GI), consistency of foot placement while stepping is important in making successful transitions from a state of stable static posture to an unstable state of dynamic locomotion. In populations characterized by gait dysfunction and postural instability, such as persons with Parkinsons disease (PD), the ability to generate a consistent stepping pattern during GI may be essential in the prevention of falls. However, little is known about GI variability in persons with PD as compared to their healthy elderly peers. Therefore, this study investigated spatiotemporal variability during the first two steps of GI in 46 persons with idiopathic PD and 49 healthy age-matched adults. Stepping characteristics, including the length, width, and time of the first two steps of GI as well as their coefficients of variation (CV) were compared between groups. Persons with PD initiated gait with significantly shorter steps (swing step length=.463 vs. .537 m, stance step length=.970 vs. 1.10 m) and higher variability in step length (swing step CV=8.82 vs. 5.45, stance step CV=6.76 vs. 3.61). Persons with PD also showed significantly higher variability in the time of the swing step (swing step CV=10.0 vs. 7.4). GI variability did not differ significantly between disease stages in persons with PD. Because greater variability in these measures during gait is related to an increased risk of falls, we propose that higher GI variability may play a considerable role in falls frequently observed during transitions from quiet standing in PD.

Emotional influences on locomotor behavior

Emotional responses to appetitive and aversive stimuli motivate approach and avoidance behaviors essential for survival. The purpose of the current study was to determine the impact of specific emotional stimuli on forward, approach-oriented locomotion. Steady state walking was assessed while participants walked toward pictures varying in emotional content (erotic, happy people, attack, mutilation, contamination, and neutral). Step length and step velocity were calculated for the first two steps following picture onset. Exposure to the mutilation and contamination pictures shortened the lengths of step one and step two compared to the erotic pictures. Additionally, step velocity was greater during exposure to the erotic pictures compared to (1) the contamination and mutilation pictures for step one and (2) all other picture categories for step two. These findings suggest that locomotion is facilitated when walking toward approach-oriented emotional stimuli but compromised when walking toward aversive emotional stimuli. The data extend our understanding of fundamental interactions among motivational orientations, emotional reactions, and resultant actions. Theoretical and practical implications are discussed.

Emotional state affects the initiation of forward gait.

The aim of the current study was to determine the extent to which pleasant and unpleasant emotional states impact the initiation of forward gait. Participants initiated gait and walked for several steps following the presentation of low arousing pleasant, high arousing pleasant, low arousing unpleasant, high arousing unpleasant, and neutral pictures. Reaction time, displacement, and velocity of the center of pressure (COP) trajectory, and length and velocity of the first and second steps were calculated. Exposure to the highly arousing unpleasant pictures reduced reaction times compared to all other affective conditions. Compared to the low arousing unpleasant pictures, exposure to the high and low arousing pleasant pictures increased the displacement of the COP movement during the anticipatory postural adjustment phase of gait initiation. Additionally, exposure to the low arousing pleasant pictures increased the velocity of the COP movement during the anticipatory postural adjustment phase, compared to the high and low arousing unpleasant pictures. Exposure to the high and low arousing pleasant pictures increased the velocity of the first step relative to the low arousing unpleasant pictures. These findings demonstrate that highly arousing unpleasant emotional states accelerate the initial motor response, but pleasant emotional states generally facilitate the initiation of forward gait due to the approach-oriented directional salience of the movement. These findings extend the scope of the motivational direction hypothesis by demonstrating the effects of emotional reactivity on the initiation of gait.

Intensity thresholds for aerobic exercise-induced hypoalgesia.

INTRODUCTION Despite many studies investigating exercise-induced hypoalgesia, there is limited understanding of the optimal intensity of aerobic exercise in producing hypoalgesic effects across different types of pain stimuli. Given that not all individuals are willing or capable of engaging in high-intensity aerobic exercise, whether moderate-intensity aerobic exercise (MAE) is associated with a hypoalgesic response and whether this response generalizes to multiple pain induction techniques needs to be substantiated. PURPOSE This studys purpose is to test for differences in the magnitude of pressure and heat pain modulation induced by MAE and vigorous-intensity aerobic exercise (VAE). METHODS Twelve healthy young males and 15 females completed one training session and three testing sessions consisting of 25 min of 1) stationary cycling at 70% HR reserve, 2) stationary cycling at 50% HR reserve, or 3) quiet rest (control). Pain testing was conducted on both forearms before and immediately after each condition and included the following tests: pressure pain thresholds, suprathreshold pressure pain test, static continuous heat test, and repetitive pulse heat pain test. Repeated-measures ANOVA was conducted on each pain measure. RESULTS VAE and MAE reduced pain ratings during static continuous heat stimuli and repetitive heat pulse stimuli, with VAE producing larger effects. VAE also increased pressure pain thresholds, whereas neither exercise influenced suprathreshold pressure pain ratings. CONCLUSION These results suggest that MAE is capable of producing a hypoalgesic effect using continuous and repetitive pulse heat stimuli. However, a dose-response effect was evident as VAE produced larger effects than MAE.

Isometric Exercise as a Test of Pain Modulation: Effects of Experimental Pain Test, Psychological Variables, and Sex

OBJECTIVE Little is known regarding whether exercise-induced hypoalgesia (EIH) produced by isometric exercise is influenced by psychological factors or systematically varies across multiple experimental psychophysical pain tests. Thus, this study sought to determine the influence of experimental pain test, psychological factors, and sex on the hypoalgesic response of submaximal isometric exercise. METHODS Healthy young males (N = 12) and females (N = 15) completed one training and two testing sessions consisting of quiet rest (control condition) or a 3-minute isometric handgrip performed at 25% of maximum voluntary contraction. Pain testing was conducted on both forearms prior to and following exercise and quiet rest. The pain tests included: pressure pain thresholds (PPT), suprathreshold pressure pain test, static prolonged heat test, and temporal summation of heat pain. Participants completed the Pain Catastrophizing Scale during the training session and the State-Trait Anxiety Inventory-State version prior to each session. The data were analyzed with mixed model analyses of variance, partial Pearson correlations, and hierarchical regression analyses. RESULTS Isometric exercise increased PPTs for men and women, reduced pain perception during static prolonged heat stimuli for women, and reduced temporal summation of pain for men and women. Greater pain catastrophizing was associated with smaller reductions in temporal summation following isometric exercise. CONCLUSIONS These findings demonstrate that the hypoalgesic response to submaximal isometric exercise is partially a function of sex and experimental pain test. Furthermore, the relationship between EIH and pain catastrophizing was psychophysical pain test specific, with greater pain catastrophizing predicting diminished EIH only during the temporal summation of pain trials.

Offset analgesia is reduced in older adults.

Summary Offset analgesia was reduced in older adults compared to younger adults when tested on the volar forearm, and was nonexistent for all subjects on the palm. Abstract Recent studies indicate that aging is associated with dysfunctional changes in pain modulatory capacity, potentially contributing to increased incidence of pain in older adults. However, age‐related changes in offset analgesia (offset), a form of temporal pain inhibition, remain poorly characterized. The purpose of this study was to investigate age differences in offset analgesia of heat pain in healthy younger and older adults. To explore the peripheral mechanisms underlying offset, an additional aim of the study was to test offset at 2 anatomical sites with known differences in nociceptor innervation. A total of 25 younger adults and 20 older adults completed 6 offset trials in which the experimental heat stimulus was presented to the volar forearm and glabrous skin of the palm. Each trial consisted of 3 continuous phases: an initial 15‐second painful stimulus (T1), a slight increase in temperature from T1 for 5 seconds (T2), and a slight decrease back to the initial testing temperature for 10 seconds (T3). During each trial, subjects rated pain intensity continuously using an electronic visual analogue scale (0–100). Older adults demonstrated reduced offset compared to younger adults when tested on the volar forearm. Interestingly, offset analgesia was nonexistent on the palm for all subjects. The reduced offset found in older adults may reflect an age‐related decline in endogenous inhibitory systems. However, although the exact mechanisms underlying offset remain unknown, the absence of offset at the palm suggests that peripheral mechanisms may be involved in initiating this phenomenon.

Emotional state affects gait initiation in individuals with Parkinson’s disease

The purpose of the present study was to determine the impact of manipulating emotional state on gait initiation in persons with Parkinson’s disease (PD) and healthy older adults. Following the presentation of pictures that are known to elicit specific emotional responses, participants initiated gait and continued to walk for several steps at their normal pace. Reaction time, the displacement and velocity of the center of pressure (COP) trajectory during the preparatory postural adjustments, and length and velocity of the first two steps were measured. Analysis of the gait initiation measures revealed that exposure to (1) threatening pictures, relative to all other pictures, speeded the initiation of gait for PD patients and healthy older adults; (2) approach-oriented emotional pictures (erotic and happy people), relative to withdrawal-oriented pictures, facilitated the anticipatory postural adjustments of gait initiation for PD patients and healthy older adults, as evidenced by greater displacement and velocity of the COP movement; and (3) emotional pictures modulated gait initiation parameters in PD patients to the same degree as in healthy older adults. Collectively, these findings hold significant implications for understanding the circuitry underlying the manner by which emotions modulate movement and for the development of emotion-based interventions designed to maximize improvements in gait initiation for individuals with PD.