Massage Reduces Pain Perception and Hyperalgesia in Experimental Muscle Pain: A Randomized, Controlled Trial

The Journal of Pain, Vol 9, No 8 (August), 2008: pp 714-721 Available online at www.sciencedirect.com

Massage Reduces Pain Perception and Hyperalgesia in Experimental Muscle Pain: A Randomized, Controlled Trial Laura A. Frey Law, Stephanie Evans, Jill Knudtson, Steven Nus, Kerri Scholl, and Kathleen A. Sluka Program in Physical Therapy and Rehabilitation Science, The University of Iowa, Iowa City, Iowa.

Abstract: Massage is a common conservative intervention used to treat myalgia. Although subjective reports have supported the premise that massage decreases pain, few studies have systematically investigated the dose response characteristics of massage relative to a control group. The purpose of this study was to perform a double-blinded, randomized controlled trial of the effects of massage on mechanical hyperalgesia (pressure pain thresholds, PPT) and perceived pain using delayed onset muscle soreness (DOMS) as an endogenous model of myalgia. Participants were randomly assigned to a no-treatment control, superficial touch, or deep-tissue massage group. Eccentric wrist extension exercises were performed at visit 1 to induce DOMS 48 hours later at visit 2. Pain, assessed using visual analog scales (VAS), and PPTs were measured at baseline, after exercise, before treatment, and after treatment. Deep massage decreased pain (48.4% DOMS reversal) during muscle stretch. Mechanical hyperalgesia was reduced (27.5% reversal) after both the deep massage and superficial touch groups relative to control (increased hyperalgesia by 38.4%). Resting pain did not vary between treatment groups. Perspective: This randomized, controlled trial suggests that massage is capable of reducing myalgia symptoms by approximately 25% to 50%, varying with assessment technique. Thus, potential analgesia may depend on the pain assessment used. This information may assist clinicians in determining conservative treatment options for patients with myalgia. © 2008 by the American Pain Society Key words: Myalgia, delayed onset muscle soreness, analgesia, manual therapy, treatment.

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usculoskeletal pain is one of the most prevalent forms of pain reported in primary care22 and for chronic pain conditions.21 However, relatively little is known regarding treatment outcomes for deep tissue muscle pain. Chronic musculoskeletal pain is a primary component in several pain syndromes that include both inflammatory and noninflammatory conditions. Approximately 10% to 15% of the US population has chronic widespread muscle pain; 20% to 50% of the population has chronic regional muscle pain.10,21 Although

Received April 6, 2007; Revised January 30, 2008; Accepted March 10, 2008. Supported by departmental funding from the Graduate Program in Physical Therapy and Rehabilitation Science at The University of Iowa. Address reprint requests to Dr. Laura Frey Law, Graduate Program in Physical Therapy and Rehabilitation Science, The University of Iowa, 1-252 Medical Education Building, Iowa City, IA 52242. E-mail: [email protected] 1526-5900/$34.00 © 2008 by the American Pain Society doi:10.1016/j.jpain.2008.03.009

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pharmacological treatment for musculoskeletal pain is common, increasingly patients and clinicians are seeking alternative therapies with minimal risk. Temporary muscle pain frequently occurs after unaccustomed eccentric exercise (muscle lengthening contractions), resulting in delayed onset muscle soreness (DOMS) 8 to 24 hours after activity.1,7,17,27,40,42 This can be used experimentally as an endogenous muscle pain model to produce sensations similar to clinical muscle pain conditions, including deep tissue muscle pain with contraction or stretch, taut bands, occasional resting pain, mechanical hyperalgesia, and the perception of trigger points.10,39 DOMS provides a controlled pain model to study therapeutic interventions, which is challenging in clinical populations due to variation in underlying pathology, concomitant interventions, and so forth. Massage has been used for rehabilitation and relaxation for thousands of years around the world, with few adverse effects. A number of different massage techniques are in use today; however, classic Western mas-

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sage, that is, Swedish massage, is the most common. Massage has been proposed to decrease tissue adhesion, promote relaxation, increase regional blood circulation, increase parasympathetic circulation, increase intramuscular temperature, and decrease neuromuscular excitability.47 However, despite its common use, there is only limited scientific evidence to support the use of massage to prevent or decrease muscle pain.4,14,19,34 Many studies combine massage with other treatments or include a range of populations, making it difficult to interpret the isolated influence of massage. For example, massage in conjunction with acupuncture reduced pain in a randomized-controlled trial (RCT) of cancer patients undergoing surgery.34 A quantified review of 9 RCTs investigating massage in pediatric populations revealed that arthritis pain was significantly reduced after multiple treatments.4 Conversely, patient satisfaction increased but pain scores did not change in an RCT involving patient choice of 1 alternative therapy (massage, chiropractic, or acupuncture) added to standard care for low back pain.14 A Cochrane systematic review of massage for neck disorders was unable to conclude whether massage had a significant effect due to the mix of findings and lack of quality studies.16 However, a Cochrane review of massage for low back pain concluded that it might be beneficial but needed additional investigation.19 Treatment for DOMS has also been investigated. Massage applied 15 minutes to 3 hours after the unaccustomed exercise but before the development of DOMS results in reduced DOMS pain relative to control conditions.23,35,49 However, once DOMS has developed, 24 to 48 hours after exercise, massage has been reported to have no effect26 as well as provide some benefit.15 Unfortunately, few well-controlled trials of massage exist either in clinical or experimentally induced pain populations. Further, the potential confounding influence of cutaneous touch is rarely considered. Thus, the purpose of this study was to determine the effects of massage using an endogenous muscle pain model in otherwise healthy individuals, using a blinded, randomized, controlled trial to compare deep soft-tissue massage, light superficial touch, and no treatment (control). We hypothesized that a single dose of deep-tissue massage would result in a reduction in DOMS pain ratings and mechanical hyperalgesia versus cutaneous stroking or no treatment.

Methods Subjects Written informed consent was obtained before participation from all study participants as approved by The University of Iowa Biomedical Institutional Review Board. Subjects were recruited from the community and campus using posted fliers and word of mouth. Exclusion criteria included current complaints of pain, a history of chronic pain, any current or past medical condition restricting exercise, a history of sensory loss or numbness in

the arms or legs, pregnancy, and the inability to understand or follow directions. Subjects were randomly assigned to 1 of 3 treatment groups: Control (no massage, quiet rest), cutaneous, light stroking of the skin (superficial touch), or treatment (deep-tissue massage of the muscles) by a random drawing. Subjects were not informed ahead of time of the 3 treatment groups. Each subject attended 2 sessions. Unaccustomed eccentric wrist extensions were performed at session 1 to induce DOMS. The treatment session, control, cutaneous, or deep massage, occurred at the second visit 24 to 48 hours after session 1. Strength, pain, and sensory testing were performed before and after exercise at session 1 and before and after treatment at session 2, by the same 2 investigators for all subjects. These investigators divided the tasks consistently across subjects and assisted each other as necessary to facilitate testing. The testers remained blinded to group assignments throughout the study. A third investigator was responsible for scheduling and random assignment, and a fourth investigator was responsible for the massage treatment. The study protocol is outlined in Table 1.

Strength Testing Maximum isometric wrist extension torque measurements were obtained for each participant using the Biodex Isokinetic Dynamometer System 3 (Biodex Medical Systems, New York, NY). Participants were positioned with their forearms secured, the wrist positioned in neutral, and the wrist lateral joint line centered with the Biodex center of rotation. Measurements were repeated 4 times: Baseline and after exercise at session 1 and before and after treatment at session 2.

Pain and Sensory Testing Several pain and sensory measurements were evaluated to assess the effect of massage on experimental muscle pain. The pressure pain threshold (PPT) has been

Table 1.

Experimental Protocol

ORDER

SESSION 1

1 2 3

Pain (VAS) at rest Pain (VAS) with stretch Pressure pain threshold (PPT) Maximum isometric torque Pain (VAS) with max contraction Eccentric exercise to fatigue (3 sets)

4 5 6

7 8 9 10 11

Pain (VAS) at rest Pain (VAS) with stretch PPT Maximum isometric torque Pain (VAS) with max contraction

SESSION 2 Pain (VAS) at rest Pain (VAS) with stretch PPT Maximum isometric torque Pain (VAS) with max contraction 6-minute treatment (deep massage, superficial, control) Pain (VAS) at rest Pain (VAS) with stretch PPT Maximum isometric torque Pain (VAS) with max contraction

Abbreviations: VAS, visual analog scale; PPT, pressure pain threshold.

716 defined as the lowest stimulus intensity at which an individual perceives mechanical pain.45 PPTs provide a means to evaluate mechanical hyperalgesia,28,36,38 where a reduction in PPT values relative to baseline indicates mechanical hyperalgesia. Four PPT values were obtained over the extensor digitorum muscle belly, each spaced approx 1 cm apart in a diamond pattern, using a hand-held digital pressure algometer (Somedic AB, Farsta, Sweden), using the 1 cm2 tip at a rate of 40 kPa/s. The mean of the 4 measures was used for each time point: Baseline and after exercise (session 1) and before and after treatment (session 2). The mean PPT values were normalized by baseline PPT values to determine relative mechanical hyperalgesia values. This measure has demonstrated good repeatability and reliability in a number of previous investigations with intraclass correlation coefficients (ICCs) between 0.95 and 0.99.12,38,46 Pain intensity was evaluated using a 10-cm visual analog scale (VAS) with the far left and right ends anchored with the phrases, “no pain” and “the worst pain imaginable,” respectively.37 Subjects were asked to mark the line indicating their level of muscle pain, discomfort, or soreness. VAS measurements were obtained at rest, during stretch, and immediately after maximum isometric contraction (Biodex 3.0; Biodex Medical Systems) at 4 time points: Baseline and after exercise (session 1); before and after treatment (session 2), for a total of 12 VAS measures. The VAS provides a valid and reliable measure of acute pain.5,8

Fatiguing Exercise To induce DOMS, subjects were asked to perform 3 sets of eccentric (lengthening) wrist extensor contractions to fatigue using a 10-lb hand weight. Fatigue was defined as the point when individuals were no longer able to control the weight during 3 consecutive eccentric (lowering phase) repetitions. Assistance during the concentric (shortening) phase of the motion using the opposite hand was permitted to encourage maximum eccentric fatigue. A short rest of approximately 1 to 2 minutes between sets was allowed. For this study, we operationally defined DOMS as increased pain with rest, stretch, or contraction of ⱖ0.5 cm on a 10-cm VAS and/or mechanical hyperalgesia of ⱖ10% change in PPTs 24 to 48 hours after eccentric exercise.

Massage Treatment All subjects were exposed to the same environmental conditions (room, music, massage cream, and therapist) for the 6-minute intervention (regardless of treatment group). Six minutes was chosen, based on the clinical practice experience of the investigators for a small region of interest. The experimental group received a deep-tissue massage to the extensor mass of the forearm, consisting of effleurage (superficial, light stroking primarily of the cutaneous layers) for 1 minute, petrissage (deep-tissue kneading of the muscles) for 4 minutes, and effleurage again for 1 minute. The superficial touch group received only effleurage of the skin without ma-

Massage Reduces Pain and Hyperalgesia nipulating the deeper tissues for 6 minutes. The control group had a thin layer of massage cream applied but received no further touch during the 6 minutes. This was done to maintain consistency and ensure blinding of the coinvestigators. Each massage was performed by the same experimenter (female) and prefaced with the statement, “if at any time the pressure is uncomfortable, just let me know and I can change it.” Subjects were escorted to a separate, quiet room and instructed to lay supine on a plinth. The same 2 songs of soothing music (Yoga Energy, BMG special products, 2002) were played in the background. The experimenter did not speak to the subject during the 6 minutes allotted for treatment. After the treatment, subjects were asked not to reveal details of their treatment to the other investigators.

Statistical Analyses To test for differences in peak torque, a 3-way mixed, repeated-measures analyses of variance (ANOVA) was used (time ⫻ sex ⫻ group), with the Huynh-Feldt correction for nonsphericity as needed.24 To test for betweengroup and sex differences in treatment effectiveness of DOMS symptoms, 2-way (treatment group ⫻ sex) ANOVA were used. When no sex differences occurred, the data were collapsed into 1 group (1-way ANOVA). The effect of treatment group on pain and hyperalgesia was evaluated by using a percent (%) reversal (absolute change after treatment normalized by pain increase between sessions 1 and 2) for pain and mechanical hyperalgesia. Post hoc testing was done using Dunnett’s t statistic, comparing the massage groups against the no-treatment control. Only subjects with the respective DOMS symptom (eg, stretch pain) at the beginning of session 2 were considered for treatment effects, operationally defined as decreased PPTs by 10% or more or increased VAS pain scores of 0.5 or greater from baseline (cohort determined separately for each measure). This approach avoided evaluating if massage decreased pain in individuals not reporting pain for a particular activity (eg, at rest), with adjusted sample sizes for each variable. Mean, standard error of the mean (SEM), and percent change values are reported. Significance was set at ␣ ⫽ 0.05.

Results Subjects Forty-four healthy individuals (22 male, 22 female) participated in this study and were randomly placed into the deep massage (n ⫽ 16), superficial touch (n ⫽ 17), and control (n ⫽ 11) groups. Mean age was 23.3 ⫾ 3.5, with a range of 19 to 41 years. All but 1 of the 44 subjects reported development of DOMS, as operationally defined. One subject (female, deep massage group) was removed from further analyses due to lack of any DOMS symptoms, as evidenced by either pain or mechanical hyperalgesia, leaving a total of 43 subjects included in the remaining analyses. Muscle pain with stretch and

Frey Law et al Table 2.

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Frequency of Delayed Onset Muscle Soreness (DOMS) Symptoms Observed MASSAGE TREATMENT GROUP

1 Resting pain ⱖ0.5 1 Stretch pain ⱖ0.5 1 Contraction pain ⱖ0.5 Mechanical hyperalgesia ⱖ10% DOMS observed (any of above)

DEEP (N ⫽ 16)

SUPERFICIAL (N ⫽ 17)

CONTROL (N ⫽ 11)

TOTAL (N ⫽ 44)

6 14 5 13 15

8 17 5 14 17

5 11 1 9 11

19 (43.2%) 42 (95.5%) 11 (25.0%) 36 (81.8%) 43 (97.7%)

mechanical hyperalgesia were the most frequent measures of DOMS (Table 2). The most inconsistent indicator of DOMS was pain during maximal contraction, with only 25% of subjects reporting this symptom.

Analyses of All Participants With DOMS Peak Torque Subjects were successfully fatigued after eccentric exercise; mean maximum torque decreased by 40.4% immediately after eccentric exercise relative to baseline (Fig 1). Although absolute peak torque values were approximately double for men than women (eg, baseline ⫽ 10.3 vs 5.9 Nm, F1,37 ⫽ 31.07, P ⬍ .0001), the relative changes in strength due to fatigue were not significantly different between men and women (F1,37 ⫽ 3.65, P ⫽ .06). Torque partially recovered at the beginning of the second session but remained significantly lower than baseline by 12.2% (F2,74 ⫽ 56.1, P ⬍ .0001). Treatment did not produce any additional torque recovery.

Muscle Pain Wrist extensor muscle pain during stretch, rest, and maximal contraction for all 43 subjects with any form of DOMS are shown in Fig 2A–C. No differences between baseline DOMS pain ratings were observed between

men and women (F1,37 ⫽ 0.19 –2.99, P ⫽ .09 – 0.67) or treatment groups (F2,37 ⫽ 0.311– 0.945, P ⫽ .40 – 0.74). DOMS significantly increased during stretch by 2.44 ⫾ 0.28 cm (10 cm VAS; F1,37 ⫽ 68.7, P ⬍ .0001) and minimally increased at rest (0.75 ⫾ 0.16 cm; F1,37 ⫽ 20.0, P ⬍ .0001). No significant increase in muscle pain during maximal contraction with DOMS occurred relative to pre-exercise ratings (0.03 ⫾ 0.24 cm; F1,37 ⫽ 0.02, P ⫽ .89). Due to the lack of increased contraction pain with DOMS, it was omitted from further analyses.

Mechanical Hyperalgesia Mechanical hyperalgesia occurred with a mean decrease in PPTs of 25.8 ⫾ 2.78% (F1,37 ⫽ 80.65, P ⬍ .0001; Fig 2D) for the 43 subjects. Absolute PPT values were significantly higher for men than women at every time point (mean baseline values: 192.3 vs 152.0 kPa/sec, F1,37 ⫽ 7.56, P ⫽ .009). However, when normalized to baseline, the relative change in PPT (eg, mechanical hyperalgesia) was not different between sexes (eg, ⫺21.9% vs ⫺29.9%, F1,37 ⫽ 2.58, P ⫽ .12). Thus, data between men and women are reported as 1 group for subsequent analyses.

Cohort-Specific Analyses Stretch and Resting Pain A significant treatment effect (F2,36 ⫽ 3.87; P ⫽ .03) was observed in the 42 subjects exhibiting pain with muscle stretch (Fig 3). No significant sex main effect (F1,36 ⫽ 1.07, P ⫽ .31) or treatment ⫻ sex interaction (F2,36 ⫽ 0.31, P ⫽ .74) occurred. Between-group post hoc tests revealed deep massage produced a reversal in stretch pain (48.4% reduction) compared with the no-treatment control (17.7% increase, P ⬍ .01), with a mean between-group difference in pain ratings of 1.1 ⫾ 0.5 cm. However, the superficial touch group was not significantly different from the other 2 groups (P ⫽ .3). Of the 19 subjects reporting DOMS at rest, there was no difference in pain reversal between sexes (F1,13 ⫽ 0.08, P ⫽ .78) or treatment groups (Fig 3): deep massage (66.5 %), superficial touch (55.2%), and no treatment (33.2%), (F2,18 ⫽ 1.14, P ⫽ .34).

Mechanical Hyperalgesia Figure 1. Mean (SEM) maximum wrist extensor torque normalized to baseline values for each treatment group. No significant group or group ⫻ time interactions were observed. *Significantly different than baseline (P ⱕ .05).

In the 36 subjects with mechanical hyperalgesia, treatment effects (% reversal) did not vary by sex (F1,30 ⫽ 0.97, P ⫽ .33) but did vary by group (F2,35 ⫽ 3.44, P ⫽ .04; Fig 3).

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Massage Reduces Pain and Hyperalgesia

Figure 2. Mean (SEM) baseline and delayed onset muscle soreness (DOMS) symptoms for all 43 subjects with any one DOMS symptom. A, pain at rest; B, pain during stretch; C, pain during maximal isometric contraction; and D, pressure pain thresholds (PPTs). *Significantly different than baseline (P ⱕ .05). Mechanical hyperalgesia was reduced by 27% after deep massage and superficial touch (27.6 ⫾ 14.7% and 27.5 ⫾ 20.4%, respectively), whereas no treatment resulted in further increased hyperalgesia by 38.4 ⫾ 20.8% (P ⫽ .02).

Discussion Deep tissue massage was able to reduce mechanical hyperalgesia (increase thresholds) and decrease stretch

Figure 3. Mean (SEM) percent reversal of DOMS symptoms in

those subjects exhibiting resting pain (n ⫽ 19), stretch pain (n ⫽ 42), and mechanical hyperalgesia (n ⫽ 36) by treatment group. *Significantly different than the no-treatment control group (P ⱕ .05).

pain relative to the no-treatment control group. Superficial touch alone was able to reverse DOMS mechanical hyperalgesia equally as well as that observed with deep massage. Further, when combining the superficial touch and deep massage groups, stretch pain reduction remained significantly greater than the control group, although independently superficial touch was not significantly better than no treatment. These results would suggest that deep-tissue massage is better than superficial touch in reducing muscle pain but that superficial touch may contribute some benefit. It is challenging to test massage relative to a placebo treatment due to the sensory feedback system, but superficial touch may provide a form of placebo intervention. However, it is likely that the no-treatment control provided little to no placebo effect. In the classically referenced report by Beecher,3 placebo responses occurred in 35% of the 15 studies analyzed (range, 21%–58%) in a total of 1082 patients. However, in low-back pain patients, as many as 65% to 70% of those studied reported pain relief with sham or discredited treatment.44 Thus, the reduction in mechanical hyperalgesia observed after superficial touch may be a placebo response. Conversely, superficial touch may involve an active treatment effect, similar to deep-tissue massage. Animal models would suggest that even light stroking can produce an anti-nociceptive response.31 Massage-like stimulation in rats increases the endogenous release of oxytocin in the plasma and the periaqueductal gray (PAG),

Frey Law et al and the antinociceptive effects are prevented by blockade of oxytocin receptors.2,31,48 Oxytocin is a hormone that has been shown to increase pain threshold, induce physical relaxation, and lower blood pressure and cortisol levels in rats. Injection of oxytocin into the PAG produces analgesia by activation of opioid receptors in the PAG.31 In humans, oxytocin has been shown to relieve cancer pain33 and low back pain48 and increase the pain threshold to colonic distension in people with irritable bowel syndrome.29 Thus, massage may decrease hyperalgesia and pain through activation of descending inhibitory pathways, using the PAG-opioid system and oxytocin. Resting pain was not altered by massage relative to control subjects but rather decreased regardless of the treatment group. However, the mean increase in resting pain intensity was low, less than 1 cm on the VAS, which may not be clinically meaningful. Indeed, DOMS is more frequently associated with movement and muscle contraction.11,32,43 Alternatively, the lack of treatment effect for resting pain may be that it is mediated by different mechanisms than stretch pain or mechanical hyperalgesia, such as central versus peripheral, or activation of chemoreceptors versus mechanical nociceptors. To assess muscle pain with contraction, we asked subjects to rate their contraction pain after performing a maximal isometric effort. DOMS is typically associated with pain with movement and muscle contraction.32 However, maximal contractions were perceived as equally painful at baseline and with DOMS, with mean pain ratings of 2.35 cm. Further, the maximum effort may have been compromised at the second session due to the DOMS. The peak torque was significantly reduced with DOMS, consistent with prior studies.11,30 Using a controlled submaximal contraction (eg, pain with lifting a constant load) may be a better measure of DOMS contraction pain for future studies. Studies involving DOMS may neglect to indicate the conditions under which pain is assessed. Our results demonstrate notable differences between pain ratings at rest, during stretch and with maximal contraction, suggesting this information is valuable. The current study demonstrates that soft-tissue massage can reduce hyperalgesia and pain using a DOMS model. Prior studies have had varied findings regarding the effects of massage on DOMS pain. Massage applied shortly after bouts of eccentric exercise (immediately to 3 hours after fatigue) but before the development of DOMS typically reduces pain associated with DOMS at 24 to 48 hours.23,35,41,49 However, Jonhagen et al26 reported no improvement in DOMS pain with massage provided both after exercise and repeated daily for an additional 2 days. Participants rated their pain before and after massage without discussion of the conditions used to elicit pain (ie, palpation, contraction, or rest). If their pain rating is analogous to what we term resting

719 pain in the current study, this may partially explain their lack of pain reduction. Some literature suggests that men and women may respond differently to pain due to different pain modulatory mechanisms such as baroreceptor reflex arch (blood pressure related analgesia)6; descending inhibitory controls20; endogenous opioid system18; and hormones, family history, and affective/cognitive factors.25 However, no sex differences were observed in this cohort for any of the pain intensity scales, consistent with prior studies involving DOMS.9,13 Our study found men to have higher absolute PPTs, a common finding.45 However, when normalized to baseline, no further sex differences were noted in relative change in PPTs with DOMS (hyperalgesia) or treatment (reversal of hyperalgesia). Further, no treatment ⫻ sex interactions were evident, suggesting that men and women responded similarly to massage. Although we observed a positive effect of deep tissue massage relative to a no treatment control, these findings may not be universally applicable. The confined analyses to those individuals reporting increased pain resulted in a reduced sample size. A type II error may have occurred for the resting pain condition, adversely influencing our conclusion that massage did not affect resting pain. Additionally, we were not adequately able to assess contraction pain using our current methodology. The results from our 6-minute Swedish massage treatment may or may not translate to different treatment durations and/or massage techniques. Although we were able to detect significant improvements in pain with a 6-minute massage from a well-trained doctor of physical therapy (DPT) student, therapist experience level may have an influence on outcomes.35 Nevertheless, advanced massage skills probably would result in greater treatment effects, not reduced. Last, DOMS provides a controlled model of muscle soreness but may not mimic precisely the peripheral and central pain mechanisms associated with other muscle pain conditions. In conclusion, the current study supports the use of massage to decrease stretch pain perception and hyperalgesia after the induction of DOMS. We have demonstrated that deep-tissue massage partially reverses stretch pain, and both deep-tissue and superficial touch treatments partially reversed mechanical hyperalgesia— the 2 most frequent measures of DOMS in this study. Several clinical implications can be drawn from these results. Even a relatively brief, 1-time treatment can produce measurable changes in muscle pain. Massage is capable of partially reversing muscle pain and hyperalgesia associated with muscle stretch and mechanical pressure but may not be able to reverse resting pain. The conditions under which muscle pain is assessed may account for some of the disparity in the literature regarding the effect of massage on muscle pain.

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