All the participants were informed about the objective and content of the project and gave written informed consent to participate in the study that conformed to The Declaration of Helsinki, and was approved by the Local Ethical Committee (H-3-2010-062). The trial was registered in ClinicalTrials.gov (NCT01478451) before the enrollment of the participants.
For clarity, this section is divided into description of the randomization process, the protocol used to induce soreness, the treatments tested, the measurements used for quantification of soreness, and finally the statistical procedures.
Using a computer-generated random numbers table, the participants were allocated to active exercise for the right or left shoulder followed 2 hours later by massage on the contralateral shoulder (n = 10), or to massage on the right or left shoulder followed 2 hours later by active exercise with the contralateral shoulder (n = 10). In this way, massage and active exercise were never performed on the same shoulder to avoid carryover effects from the first to the second round. In both situations, the passive shoulder served as control. In this way, data for active exercise, massage and control were obtained for all the participants, allowing for a balanced and paired statistical design. One author (L.L.A.) performed the randomization, and a physical therapist informed the participants of their respective allocation.
Induction of Soreness
Using a Biodex Medical isokinetic dynamometer (System 3 Pro, Brookhaven R&D Plaza, NY, USA), the participants performed eccentric contractions for the upper trapezius muscle during the first visit to the laboratory. The participant was standing erect with arms to the side and performed maximally resisted shoulder shrugs through a full range of motion. The participant relaxed the shoulders when the handle of the dynamometer traveled upward (i.e., the concentric phase) and resisted with maximal voluntary effort when the handle traveled downward (i.e., the eccentric phase). The participants performed 3 low- to moderate-intensity warm-up sets with 15 repetitions and then a total of 10 sets with 10–15 repetitions of maximal voluntary eccentric contractions: 10 repetitions at slow velocity (30°·s−1) during the first 4 sets, 15 repetitions at medium velocity (60°·s−1) during the next 4 sets, and 15 repetitions at high velocity (90°·s−1) during the final 2 sets. One minute of rest was given between each set. A computer screen provided visual feedback of the force output during all sets. Delayed onset muscle soreness presented 48 hours later. The participants were asked to refrain from physical exercise during the 48 hours after eccentric exercise.
On the second visit to the laboratory, that is, 48 hours after the eccentric protocol, the participants were randomly assigned to receive one of the aforementioned combinations of massage and active exercise. The duration of 10 minutes for both treatments was chosen from a practical perspective, that is, to achieve a certain degree of warm-up yet not too long to fatigue the muscles and hinder implementation in most field settings.
For the massage protocol, an experienced massage therapist provided 10 minutes of massage on the right or left upper trapezius muscle while the contralateral shoulder was made to relax. The participant was lying prone on a massage couch. Massage involves various types of pressure, friction, and rubbing (22). In this study, the therapist used both petrissage, that is, kneading and friction, and effleurage, that is, a succession of light and deep stroking and gliding motions. The force used was adjusted according to the participant's level of soreness.
For the active exercise protocol, the participant performed unilateral shoulder shrugs with the Thera-Band elastic tubing, that is, elevating one shoulder while relaxing the contralateral shoulder. The participant was standing erect with 1 foot on the elastic tubing, which was elongated to 150% of resisting length. Within a 10-minute period, the participants performed 10 sets with 10 repetitions for a total of 100 repetitions. The participants used red elastic tubing during the first 3 sets, green elastic tubing during the next 3 sets, and blue elastic tubing during the final 4 sets, corresponding to 2-, 3-, and 4-kg resistances, respectively (1). Each set was completed in approximately 20 seconds allowing for 40 seconds of rest between sets.
The primary outcomes determined 48 hours after the eccentric protocol were differences between the experimental shoulder compared with the control shoulder in (a) perceived soreness and (b) PPT of the upper trapezius muscle from immediately before treatment to 0, 10, 20, and 60 minutes after treatment (Table 2). For descriptive purposes and to habituate the participants with the test procedures, these measurements were also performed during the first visit to the laboratory before the eccentric protocol (Table 1).
The participants were asked to rate perceived soreness of the left and right trapezius muscle on a numerical rating scale of 0–10, where 0 is “no soreness” and 10 is the “worst imaginable soreness.” The rating scale was horizontally oriented to represent a modified visual analog scale (33).
Using an electronic pressure algometer (Somedic, Hörby, Sweden), an examiner blinded to group allocation measured PPT of the left and right upper trapezius muscles. The contact area of the circular probe was 1 cm2. Pressure was applied at a rate of 30 kPa·s−1 perpendicular to the skin at the 5 points in each side: at the midbelly of the muscle and 1 and 2 cm laterally and medially of this point. For the upper trapezius, the midbelly was determined as midway between the acromion to the seventh cervical vertebrae. The participant was instructed to clearly state when the sensation of “pressure” changed to “pain.” At each time point (immediately before and 0, 10, 20, and 60 minutes after the intervention), PPT was measured once at each of the 5 measurement sites in both the right and the left trapezius. Subsequently, PPT was expressed as the average value of the 5 sites for each shoulder at each time point. Previous studies have shown satisfactory to good test-retest reliability of PPT (32,38).
Because outcome expectations can influence subjective pain ratings (34), we included the following question in the screening questionnaire: “To what extent do you believe that the following affects muscle soreness in the neck and shoulders?” (a) massage and (b) active exercise with elastic resistance. The response options were “causes less soreness,” “causes no change in soreness,” and “causes more soreness.”
Power calculations performed before the study showed that 20 participants in a paired design were necessary for testing the null hypothesis of equality of treatment at an alpha level of 5%, a statistical power of 80%, an SD of 1.5 and a minimally relevant difference in the intensity of soreness of 1 on a scale of 0–10 (15).
Using the Mixed procedure of SAS (SAS institute, Cary, NC, USA, version 9.2), we performed a repeated measures 2-way analysis of variance to model the changes in (a) perceived soreness and (b) PPT. The independent variables treatment (massage, active exercise, control), time (immediately before and 0, 10, 20, and 60 minutes after treatment) and the interaction treatment by time were entered in the model as fixed effects. Subject (i.e., each individual participant) was entered in the model as a random effect. When a significant main effect or interaction was found post hoc tests were performed to locate differences. The values for each treatment at the different time point are reported as means (SD) and differences between treatments at each time point as least square means (95% confidence intervals), unless otherwise stated. The p values of <0.05 were accepted as statistically significant.
On an exploratory basis, we tested the influence of outcome expectations on the change in perceived soreness and PPT by entering outcome expectations (“causes less soreness,” “causes no change in soreness,” and “causes more soreness”) and time (immediately before and 0, 10, 20, and 60 minutes after treatment) and outcome expectations by time in the analysis of variance stratified for treatment.
Finally, we calculated effect sizes as Cohen’s d (13) at each time point (between-group differences divided by the pooled SD).
Table 1 shows descriptive characteristics of the participants. At baseline, before the eccentric protocol (i.e., day 1), perceived soreness was 0.8 (1.1) on a scale of 0–10, and PPT was 197 (75) kPa. 48 hours later (i.e., day 3), immediately before treatment perceived soreness was 5.0 (2.2) and PPT 138 (78), showing induction of DOMS.
Complete data were obtained for all the 20 participants according to the randomization. A significant treatment by time interaction was found for perceived soreness (p < 0.001) and PPT (p < 0.05). Table 2 shows least square mean differences and 95% confidence intervals for perceived soreness and PPT between the treatments at the different time points. Compared with control, both active exercise and massage significantly reduced perceived soreness and increased PPT at most time points. No significant differences were observed between massage and active exercise at any time points, although compared with control, only massage showed significant effect on PPT at 0 minutes and only active exercise showed a significant effect on perceived soreness at 60 minutes.
Figure 2 illustrates the timewise change in perceived soreness and PPT. Perceived soreness adapted quickly, with the greatest effect observed immediately after treatment. Pressure pain threshold adapted more slowly, peaking 20 minutes after treatment.
Table 3 shows effect sizes at the different time points. For intensity of soreness (pooled SD = 2.2), a moderate effect size was observed immediately after treatment leveling of to a small effect size after 20–60 minutes. For PPT (pooled SD = 78), effect sizes were small at all time points.
Based on the screening questionnaire replies, outcome expectations were higher for massage than for active exercise (χ2, p < 0.05, Table 1). Exploratory analyses showed that there was no significant outcome expectation by time interaction for perceived soreness and PPT for either treatment, that is, outcome expectations did not significantly influence the outcome.
There were no reported adverse events in response to massage or active exercise.
This is the first randomized controlled trial to directly compare the timewise effect of massage with exercise for relieving muscle soreness. Our study showed acute reductions of soreness in women with DOMS in response to both active exercise and massage compared with a control condition. The magnitude and timewise change of soreness and PPT were comparable between the 2 treatments.
The eccentric protocol used in our study resulted in DOMS as evidenced by the markedly lowered PPT and increased perceived soreness at 48 hours. Many previous studies have used pressure algometry to obtain information on the level of muscle tenderness in musculoskeletal pain conditions (2,36,39). The levels of perceived soreness and PPT induced by the eccentric protocol in our study were comparable with the levels commonly observed in patients with chronic musculoskeletal disorders (3,5,18,21,29,30,35), and with the levels observed in athletes subjected to unaccustomed eccentric exercise (10). Thus, the eccentric protocol used in our study induced adequate levels of muscle soreness as compared with other study populations.
Previous studies have investigated the acute analgesic effects of exercise on muscle soreness. Zainuddin et al. investigated the effect of very light concentric exercise performed as 10 sets of 60 continuous elbow flexions (a total of 600 repetitions in 25 minutes) compared with no treatment on DOMS and muscle function 1, 2, 3, 4, and 7 days after strenuous eccentric exercise for the elbow flexors. In that study, muscle soreness was alleviated immediately after the light exercise bouts on days 1–4, whereas no effect on plasma markers of catabolism was observed at day 7. Thus, based on that study, the effect of light exercise on muscle soreness appears to be temporary without aiding recovery. However, to provide better practical guidelines, determining the duration of this temporary effect is important. Our study used a different timewise approach than Zainuddin et al. and measured soreness several times during the hour after treatment at 48 hours after eccentric exercise. Our study elaborates on the findings by Zainuddin by showing that the maximal benefit of exercise is achieved within the first 20 minutes after treatment. Also, the study by Zainuddin reported a decrease in muscle strength immediately after the light concentric exercise bouts consisting of 10 times 60 repetitions, suggesting that less volume may be preferred to avoid decrements in performance. In our study, we chose not to measure muscle strength continuously in the follow-up hour after treatment because such repetitive measurements can affect the perception of soreness and thus bias the results.
The intensity of active exercise for relieving DOMS may also be important. Andersen et al. showed that high-intensity strength training using resistance levels of 70–80% of 1 repetition maximum (∼10–15 kg during the shrug exercise) increased pain immediately after exercise in untrained women with trapezius myalgia, that is, chronic soreness of the trapezius muscle (3). In this study, the intensity during the shrug exercise was low to moderate, that is, progressing from red to blue thera-bands equivalent to 2–4 kg—during the 10 sets of 10 repetitions. In the study by Zainuddin, the intensity was likely lower than in our study, that is, the participants were able to perform 600 repetitions in 25 minutes (40). Thus, low to moderate intensities appear to effectively and safely relieve soreness, whereas high intensities may not.
Previous studies have also investigated the acute analgesic effects of massage on muscle soreness, but few well-designed randomized controlled trials exist (28). Frey Law et al. investigated in a randomized controlled trial the effect of deep-tissue massage applied to the forearm extensors (2-minute petrissage and 4-minute effleurage) compared with no-treatment or a sham intervention on DOMS at rest and during stretching 48 hours after strenuous eccentric exercise for the wrist extensors. In that study, the authors reported a decrease in stretching pain and PPT after deep-tissue massage compared with the no-treatment group, but no significant between-group difference in resting pain despite a numerical difference. In our study we found a significant positive effect of massage on resting muscle soreness. The number of subjects in each experimental group in the study by Frey Law was approximately the same as in our study, but in contrast to their study, we used a paired design allowing for greater statistical power per subject. Nevertheless, both studies support that massage can reduce symptoms of DOMS. Our study elaborates on the previous findings by showing that the maximal benefit of massage is achieved within the first 20 minutes after treatment and diminishes within an hour.
In adults with musculoskeletal pain, a change in pain intensity of 1 on a scale of 0–10 is considered the minimally relevant difference and a change of 2 is considered to be moderately clinically meaningful (15). In our study, soreness decreased on average by 1 on a scale of 0–10 compared with the control shoulder, equivalent to the minimal relevant difference. A clinical relevant change in PPT may be more difficult to define; therefore we included effect size calculations. According to Cohen, effect sizes of 0.20 are small, 0.50 moderate, and 0.80 large (13). In our study, effect sizes were moderate for the acute change in intensity of perceived soreness and small for change in PPT (Table 3). Thus, this study shows only small to moderate effects of massage and active exercise for relieving DOMS.
The effect of both massage and active exercise peaked immediately after treatment for perceived soreness and 20 minutes after treatment for PPT. The different timewise change in perceived soreness and PPT indicates that several mechanisms with different timewise influence could have acted in concert. Massage stimulates cutaneous receptors (20), potentially causing local lateral inhibition of pain feedback in the spinal cord. The stretch of and force applied to the muscle fibers from the different massage techniques also activate Ia afferents and Golgi tendon organs (9,17). The activation of these larger rapidly conducting nerve fibers could partially block the smaller, slower conducting nerve fibers detecting pain (37). Likewise, dynamic active exercise inherently activates various receptors such as Ia afferents, Golgi tendon organs, and cutaneous receptors. Thus, the gate control theory (27) may partly explain the acute reduction in soreness from both types of treatment. As another possible mechanism, massage also increases lymphatic drainage and squeezes out metabolic waste products and pain mediators such as histamines and bradykinins (20,31). Increased blood flow in response to active exercise may also provide washout of metabolites, and increased muscle temperature from the energy released during active exercise may make the sore muscles more compliant. By contrast, massage does not cause an elevation in muscle temperature (24). Thus, although the reduction in soreness was equivalent between massage and exercise, different mechanisms may have acted.
Placebo is a potential mechanism to influence subjective pain ratings (25). Before the study, 90% of the participants expected massage to reduce soreness and only 10% expected no effect or worsening from massage. By contrast, only 55% of the participants expected active exercise to reduce soreness and 45% expected no effect or worsening. Because the outcome expectations are known to influence subjective pain-related outcomes (34) placebo effects could have influenced especially the results of massage. However, exploratory analyses did not confirm a statistically significant influence of outcome expectations on the change in soreness in this study. Thus, it is conceivable that placebo effects only minimally influenced our results.
There are both strengths and limitations of our study. The randomized design and blinding of the examiner increase the validity of our results. The paired design allows for high statistical power with relatively few subjects, that is, 20 in this study. By contrast, power calculations showed that an unpaired design with 3 independent groups would require 36 in each group, that is, a total of 108 participants. Thus, economizing the number of participants using a paired design to compare the effect of massage and active exercise is both scientifically and ethically sound. However, a possible crossover effect from the experimental shoulder to the control shoulder may have underestimated the true treatment effect, causing only small to moderate effect sizes. This can be visualized in Figure 2, where the control shoulder also shows improvement over time. Thus, our estimates are likely conservative. Carryover effects from the first to the second test round can also underestimate true effect sizes, but because each shoulder received only one of the treatments while the other served as control this could only have minor impact on our results. Because DOMS most commonly occurs in response to unaccustomed physical exertion, we used untrained subjects. However, this also limits the generalizability of our findings, and future studies should compare the effectiveness of massage and exercise on soreness in trained athletes and in adults with chronic musculoskeletal disorders. Finally, future studies should include measures of muscle function and mechanisms of acute pain adaptation.
In conclusion, active exercise using elastic resistance provides similar acute relief of muscle soreness as compared with that by massage, and both treatments are superior to no treatment. For both types of treatment, the greatest effect on perceived soreness occurred immediately after treatment, whereas the effect on PPT peaked 20 minutes after treatment. Altogether, the greatest effects were observed within the first 20 minutes after treatment and diminished within an hour.
Active exercise using low to moderate resistance and massage provided equal relief of muscle soreness with the greatest effects occurring during the first 20 minutes after treatment. The present knowledge provides more flexible treatment options for athletes, coaches and therapists needing to acutely relieve DOMS. For example, the coach can safely advise the athlete to do a gradual warm-up with active exercise rather than visiting the massage therapist when muscle soreness is present. We recommend using fairly light resistance during the first few sets of active warm-up and gradually increasing the resistance to tolerable levels during the later sets. However, athletes, coaches, and therapists should be aware that the effect is greatest during the first 20 minutes after treatment and diminishes within an hour. Thus, actively warming up the muscles relieves DOMS only temporarily and should be performed immediately before competition or strenuous work. Although not investigated in this study, stretching cannot be recommend for muscle soreness as a Cochrane review concluded that stretching neither prevents nor relieves exercise-induced DOMS (23).
The authors thank physical therapists Louise Houg Bengtson and Martina Dyrberg for practical assistance during the project and the Hygenic Corporation for supporting the study. The authors have no conflicts of interest to declare. The results of this study do not constitute endorsement of any product by the authors or the National Strength and Conditioning Association.
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Keywords:Copyright © 2013 by the National Strength & Conditioning Association.
hyperalgesia; delayed onset muscle soreness; experimental pain; algometry; physical exercise; intervention