Immediate Effects of Acupuncture on Force and Delayed Onset of Muscle Soreness

Abstract

Background: The ability to produce force is critical to several daily activities. Strategies to reduce delayed onsent muscle soreness (DOMS) and restore force-generating properties that occur in response to training and impair physical performance have been proposed. Acupuncture has been proposed to accelerate recovery and optimize muscle functioning. It was to determine the effects of acupuncture on DOMS and on the muscle force production capacity.

Methods: Thirty physically active volunteers (26.3 ± 3.1 years old, 1.70 ± 0.08 m, 66.5 ± 12.6 kg) were allocated in a control (CG; n = 10), placebo (PG; n = 10), and acupuncture (AG; n = 10) groups. The groups were subjected to an exercise protocol to induce DOMS and were assessed for muscle force, threshold, and rate of perceived pain and activation of the biceps brachialis muscle before (PRE) and 20 minutes after (POST) a single acupuncture session using a mixed model analysis.

Results: The threshold and rate of perceived pain were reduced in the AG (P < 0.05) but remained unchanged in the other groups (P > 0.05). Muscle activation also showed larger changes in the AG in comparison with the other groups (P < 0.05). No changes in the ability to produce force were found after acupuncture in any groups (P > 0.05).

Conclusions: Acupuncture may reduce discomfort and improve muscle activation but was not effective to promote force improvement and/or restore the force-generating properties. It may be speculated that muscle disruption may have played a role and did not allow participants to restore their muscular performance.

Rebec Number; RBR-8bh5k7 (www.ensaiosclinicos.gov.br/rg/RBR-8bh5k7); Clinical Trial Registry (UTN No.: U1111-1234-9553).

Introduction

Strength is an essential component for functionality, mobility, and performance in several physical activities and sports.¹ In tradition, strength can be incremented through resistance training programs in which muscles and tendons are exposed to moderate/heavy training loads.^2,3 However, the mechanical stress induced by traditional resistance exercises causes some degree of exercise-induced muscle damage, even in trained individuals.⁴

Muscle damage is usually assessed through a set of proxy markers such as increases in muscle swelling, blood creatine kinase concentration, delayed onset muscle soreness (DOMS), reduced joint range of motion, and diminished ability to generate force. The changes in these proxy markers last from 1 to 7 days depending on the muscle damage magnitude.⁵ Evidence suggests that decrease in muscle force production capacity is one of the main muscle damage proxy markers, presenting significant correlations with skeletal muscle morphological indices, such as Z-line streaming and lack of desmin stain.⁶

The 2 most incapacitating muscle damage symptoms are the DOMS and reduction in muscle force production capacity, due to the burden on physical performance and daily life activities. Several strategies have been designed to alleviate the severity of DOMS and to restore muscle functioning. These strategies include the use of nonsteroidal anti-inflammatory drugs,⁷ cryotherapy,⁸ massage,⁵ homeopathy, ultrasound, electrical stimulation, static and passive stretching,⁹ and physical exercise.¹⁰ Recently, acupuncture has been proposed as a viable strategy to accelerate the recovery of muscle functioning and performance in physically active individuals.^11–15 There is evidence that acupuncture reduces discomfort and pain,^16–18 which may lead to improved (or restored) muscle functioning and performance. However, no study has analyzed the acute effects of acupuncture on pain rating and threshold, and muscle force production capacity. Therefore, this study aimed to determine the effects of acupuncture on DOMS and muscle force production capacity after intense exercise designed to produce muscle damage.

Methods

In total, 52 subjects volunteered to participate in the study. Participants with upper limb articular and muscular conditions that could affect muscle strength (tendinitis, bursitis, recent fractures, etc.), hypertension/hypotension, and/or under the effect of drugs (corticoids, psychotropic, anti-inflammatory, and analgesic) were excluded from the study. In addition, participants with excessive fear of needles were not included. Participants should have at least 2 years of resistance training experience, in which the biceps curl exercise was part of their training routines. Participants were considered as physically active (i.e., exercised from 2 to 3 times per week using light to moderate intensities) before the commencement of the experiment. Thirty participants (12 men and 18 women; 26.3 ± 3.1 years old, 1.70 ± 0.08 m, 66.5 ± 12.6 kg) met the inclusion/exclusion criteria. Participants were randomly assigned to one of the following groups: acupuncture group (AG; n = 10), placebo group (PG; n = 10), and control group (CG; n = 10). The experimental procedures of this study were approved by the Ethics Committee of the Worker's Hospital (Approval No. CAAE: 23187113.7.0000.5225). After being informed of the risks and benefits associated with the participation in this study, participants signed an informed consent form.

Experimental design

This was a parallel group repeated measures design, in which participants from the AG, PG and CG performed 3 testing sessions. In all testing sessions, pain threshold test (i.e., algometry [ALG]), rating of perceived pain (i.e., visual analogic scale [VAS]), maximal voluntary isometric contractions (MVICs), and muscle activation (i.e., surface electromiography [EMG]) were assessed. In the first experimental session, participants got acquainted with the experimental procedures and performed assessment 1 (ALG, VAS, MVICs, and EMG). Forty-eight hours after assessment 1, participants returned to the laboratory for session 2. In this session, participants performed the exercise-induced muscle damage protocol. The exercise protocol consisted of 3 sets of 8–12 repetitions of the biceps curl exercise to concentric failure. Two to 3 minutes of rest was imposed between sets, and verbal encouragement was provided throughout the sets. Before and after (2 minutes after) the exercise protocol, muscle damage proxy markers were assessed in a manner similar to session 1. Twenty-four hours after session 2, participants underwent the actual experimental session (session 3). Initially, muscle damage proxy markers were assessed before the allocated treatment (i.e., PRE). Then, CG remained sited for the duration of the acupuncture intervention, PG received (whatever it was), and the AG received the acupuncture treatment. After the experimental intervention, muscle damage proxy markers were reassessed (i.e., POST). Figure 1 displays a pictorial view of the allocation procedures and experimental design.

FIG. 1.

Schematic representation of the experimental design.

Experimental interventions

The CG followed the same assessment procedures performed by the other groups but remained laying down (blindfolded) for 20 minutes with no intervention. The PG received the same treatment and the same acupuncture maneuvers, except by the fact that the needles only touched the skin but were not inserted (i.e., pricking). Blindfolding the participants was effective as 95% of the PG reported a series of typical symptoms produced by the acupuncture (dull sensation—deqi). In addition, the PG participants were sure they had needles inserted when they were asked whether they received the actual acupuncture treatment. The participants of the AG were positioned in a prone recumbent position and sterile stainless-steel acupuncture needles (Dongbang, 0.25 × 40 mm) were inserted perpendicularly to the skin with the aid of a guide tube at the points IG4, IG11, E36, and VB34 by a qualified and experienced acupuncturist. Before introducing the needles, puncture sites were cleaned with sterilized gauze bathed with isopropyl alcohol. The session lasted for ∼20 minutes. After the needles were removed, skin was cleaned and adhesive tape was placed over the puncture sites and participants remained laying down for an additional 10 minutes before the final (POST) assessment. These sites were chosen because they are described as having analgesic effects in the traditional Chinese Medicine.^3,19–21 The anatomical location of these sites can be found elsewhere.²² Participants were blindfolded during the experimental procedures, irrespective of their groups.

Pain threshold

Pain threshold was assessed using a pressure algometer (Wagner, model Force Dial TM FDK/FDn) with capacity of 30 kgf/300 N and pressure end diameter of 1 cm. Participants were seated with the arm supported in the armrest of a chair, while the algometer was positioned on the most prominent aspect of the biceps belly. Then, a constant pressure was applied until the participant reported a strong discomfort, from which test was interrupted. The interobserver reliability of the pain threshold test is deemed as high.^23,24

Perceived rating of pain

The perceived rating of pain was assessed using the VAS. Participants were requested to mark their perceived pain rating in a scale ranging from 0 to 10, where 0 represented no pain at all and 10 the most unbearable pain. The reliability of the VAS for measurement of acute pain has been deemed as high.²⁵

Maximal voluntary isometric contraction

The MVIC was assessed at the nondominant side with the participants seated on a chair. Participants performed a couple of submaximal trials in an attempt to reduce learning effects, while minimizing the repeated bout effect. During the actual tests, the shoulder was positioned in a neutral position and the elbow was flexed at 90° with respect to the vertical and the forearm supported at the chair armrest. A velcrum strap firmly secured the cable of the load cell, which was fixed perpendicularly to the forearm, at the wrist level. Verbal encouragement was provided during the 10 seconds in which participants were required to exert a maximal effort. Three maximal trials were recorded, and the peak force was used for comparison purposes. An interval of 5 minutes was allowed between trials. The load cell (model IK-1C; Kratos, Brazil) was anchored to the ground by a set of steel cables and provided the force–time traces of each MIVC. An A/D board (model NI USB 6218; National Instruments, USA) was used to convert signals to a personal computer. Signals were sampled at 2,000 Hz and analyzed using a specific software (LabVIEW Signal Express 3.0; National Instruments, USA) to identify the peak force (defined as the largest force exerted during the MVIC test).²⁶ Figure 2 depicts the experimental setup during the MVIC test.

FIG. 2.

Experimental setup to determine MVIC of the elbow flexor muscles. MVIC, maximal voluntary isometric contraction.

Muscle recruitment

The recruitment of the biceps brachialis was assessed during the MVIC test. Surface electromyography signals were sampled at 2,000 Hz (model Trigno Wireless; Delsys). The electrode was positioned according to the SENIAM recommendations.²⁷ Before electrode placement, the skin was shaved and cleaned with gauze bathed with isopropyl alcohol. Electrode position was marked on the skin with semipermanent ink to reposition the electrodes accurately between assessments and sessions. The EMG data were filtered using a fourth order Butterworth filter with a cutoff frequency set at 20–500 Hz. The root mean square (RMS) of the surface EMG signal was calculated in Windows of 1 second centered around peak force.

Statistical approach

Initially, the D'Agostino and Levene tests were applied and confirmed normality and homogeneity, respectively. Sessions 1 and 2 were also used to determine the stability of the measurements. An independent t-test was implemented for each dependent variable. The magnitude of the exercise-induced muscle damage was assessed on sessions 2 and 3 using a mixed model having group and time as fixed factors and participants as a random factor. Finally, the acupuncture effect on hampering the increase in the exercise-induced muscle damage proxy markers was determine using a mixed model having group and time as fixed factors and participants as random factor. All of the statistical analyses were conducted using the SAS 9.2^® Software and the significance level was set at P < 0.05.

Results

The analyses showed assessments produced stable values with no difference between the first and second assessments (P < 0.05). Therefore, data from the first assessment (assessment 1) were omitted and only the data from the second assessment (assessment 2) are presented. Thus, variations within and between AFTER-to-PRE and PRE-to-POST sessions were assumed as exercise-induced or treatment-induced changes, respectively. All muscle damage proxy markers reduced significantly between assessment 2 and AFTER (P < 0.05) on session 2, indicating that the exercise protocol was effective to cause muscle damage. Pain threshold reduction and increased perception experienced by all groups (P > 0.05) are a strong indication that the stimuli were equivalent before the interventions. The perceived rating of pain was above 6 points immediately before the intervention (PRE) and indicated an important effect of the protocol applied to induce pain.

All groups experienced diminished MVICs immediately after the protocol applied to induce DOMS (∼30%; P < 0.05), which was still reduced by 21% before (PRE; P < 0.05) applying the interventions. After intervention (POST), the MVICs remained relatively stable (P < 0.05) and corresponded to ∼20% of the initial condition (assessment 2). No differences were identified in the MVICs measured PRE or POST interventions in any group (P > 0.05). Figure 3 presents the relative changes in MVICs (normalized with respect to the initial condition; assessment 2) of the experimental groups before (PRE) and after (POST) intervention.

FIG. 3.

MVIC of the elbow flexor muscles from the CG, PG, and AG before (PRE) and after (POST) the acupuncture session. AG, acupuncture group; CG, control group; PG, placebo group.

The perceived pain prior intervention indicated a moderate discomfort in response to the exercise, which was similar between groups (P > 0.05). The perceived pain increased 24 hours after the protocol used to induce muscle pain in all groups (P < 0.05), but no differences between groups were detected (P > 0.05). After the intervention (POST), the placebo (GP) and the control group (CG) reported no changes in the perceived pain, which remained comparable (P > 0.05) with that observed before the interventions (PRE). In contrast, the AG showed a reduced perception of the pain after the intervention (P < 0.05), which was similar to that observed immediately after the DOMS exercise protocol. The mean pain threshold after the exercise protocol was 7.3 kgf and did not differ between groups (P > 0.05). The pain threshold before the interventions indicated less tolerance (∼60% less) to the stimuli in all groups (P < 0.05) 24 hours after the protocol designed to induce DOMS. No differences were detected between groups (P > 0.05). Postintervention data (POST) showed a negligible change in the pain threshold of the CG and PG, however, the AG presented a large recovery (P < 0.05) with respect to the other groups, which was equivalent to that observed immediately before the protocol designed to induce muscle damage (assessment 2). Figure 4 shows the rate of perceived pain and pain threshold of the experimental groups before (PRE) and after (POST) intervention.

FIG. 4.

Rate perceived pain (upper panel) and pain threshold (lower panel) of the CG, PG, and AG before (PRE) and after (POST) the acupuncture session. *Indicates differences between groups (P < 0.05).

Figure 5 presents the muscle activation (RMS) of all groups before (PRE) and at the end of the interventions (POST). Muscle activation was increased by ∼50% with respect to the baseline but did not differ between groups before intervention (PRE; P > 0.05) or was influenced by the interventions (POST; P > 0.05).

FIG. 5.

Muscle activation of the biceps brachialis muscle (% RMS) from the CG, PG, and AG before (PRE) and after (POST) the acupuncture session. RMS, root mean square.

Discussion

Reducing discomfort and DOMS is of interest of those involved in athletic performance and active life style. Protocols that cause immediate pain relief are even more attractive as short recovery periods between training and competitions are required. Thus, accelerating recovery may help to improve performance and to reduce training-related muscle discomfort. The results of this study corroborate with the hypothesis that acupuncture has immediate effects on the threshold and the rate of perceived pain. This is further evidenced because the PG was not able to identify whether they received or not acupuncture treatment at the end of the intervention session. Thus, psychologic effects may be discarded.

In this study, a large proportion of the participants of the PG thought they had received active acupuncture treatment and also reported a series of typical symptoms produced by the acupuncture (dull sensation—deqi). Some studies have reported controversial results in PGs after treatment.^28,29 It may be related to the fact that they inserted needles in some part of the bodies, which may stimulate encephalic trunk pathways and activate the descending pain control routes that may provide analgesic effects.³⁰ Therefore, pain inhibition may have occurred, irrespective of the site the acupuncture stimuli were applied, and some procedures may not be considered as a “true placebo.” The light touch applied on the acupuncture site used in the PG is encouraging to rule out analgesic effects from intervening mechanisms such as the diffuse noxious inhibitory control that are related to the acupuncture treatment (i.e., nociceptive ascendant or descendent of pain control).

Although the experimental approach does not allow the identification of the underlying mechanisms responsible for increasing the threshold and decreasing the rate of perceived pain, it was possible to conclude that the acupuncture protocol provided a clear positive immediate effect. This is in agreement to the findings of other studies in which a complete symptom clearance was obtained only 7 days after a single acupuncture treatment session.³¹

This is the first study to demonstrate improved pain perception and increased (i.e., restored) pain threshold immediately after an acupuncture intervention. It must be viewed with caution, as reducing pain perception or increasing pain threshold is not related to a complete recovery of the underlying tissues, which may take several days.³² Therefore, subjecting the muscles to maximal or submaximal exertions without a complete recovery process may increase the muscular damage even further, especially if the threshold and/or perception of the pain are dampened due to the analgesic effect of the acupuncture. It seems that the procedures applied before the intervention diminished the pain threshold and increased the perception of the discomfort.

Despite the fact that pain was reduced in response to the acupuncture intervention, no effects were observed in the ability to generate force. It is interesting to note that even after relieving the pain symptoms, force was not restored. It suggests that strength itself may not be modulated by pain. It must be considered the fact that the muscle damage induced in this study is within a “realistic” stress that is generally applied in training sessions. More pronounced induced damage may present different outcomes and warrants further investigation.

The increase in the EMG activity after acupuncture is not unexpected. The reduction in pain threshold and perception may have decreased afferent signal to the central nervous system (SNC). It has been demonstrated that pain afferent signal may inhibit spinal and supraspinal centers decreasing the efferent drive to skeletal muscles and, therefore, muscle activation.³³

As a general finding, muscle activation increased after the exercises and was reduced after the resting period. It reflects a large central activation to achieve a maximal or submaximal force.³⁴ Thus, the accelerated ability to restore the initial activation status after a single acupuncture session may be viewed as positive treatment outcome.

This study has a number of limitations such as the reduced number of participants, the specific point of acupuncture, and the amount of muscle damage induced. Larger numbers are required to strengthen the present findings. The use of different acupuncture points may also influence the results as there is no consensus in terms of precise needle insertion. Besides, it is likely that even shallow needling may trigger mechanoreceptors and cause microtrauma leading to analgesia, thus, other studies are required to minimize such effects. The protocol applied to induce muscle damage caused a “physiologic” stimulus, which is generally applied in exercise routines; however, more intense damage (derived from heavy training) may require longer intervention periods and, thus, produce different outcomes. In addition, this study was limited to a single acupuncture session (transversal study) and the effect of a more comprehensive treatment is still required (longitudinal study).

Conclusion

It was concluded that a single acupuncture session has immediate effects on muscle activation. It was also observed that acupuncture provided an analgesic effect that was able to modulate pain rating and threshold. Despite the changes in muscle activation and pain, no modifications were observed in the ability of the muscles to produce strength. It may be speculated that despite the benefits of acupuncture, muscle disruption caused by strenuous exercise was still present and may have impeded a full recovery of the ability to produce force.

Stricta

Traditional Chinese acupuncture was applied to observe it could alleviate delayed onsent muscle soreness (DOMS) due its properties to relief pain. In addition, it was also observed if acupuncture was able to restore muscle strength during a period of DOMS, which is a common acute symptom after sport and vigorous physical activity practices. As far as we are aware, no studies have explored this issue. Four needles (Dongbang, 0.25 × 40 mm) were inserted in each session at the points IG4, IG11, E36, and VB34. Needles were manually inserted at superficial level and were maintained in place during ∼20 minutes. A short-term treatment (acute) was applied by an experienced and qualified acupuncturist immediately before and after an extenuating set of exercises that intended to cause DOMS. A control group (sham) was applied in which needle insertion was simulated while subjects were blindfolded.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

To receive CME credit, you must complete the quiz online at: www.medicalacupuncture.org/cme

CME Quiz Questions

Article learning objectives: After studying this article, participants should be able to identify the immediate effects of manual acupuncture in the delayed onset of muscle soreness after exhausting exercise; identify the immediate effects of manual acupuncture on force development capacity after exhausting exercise; and explain the role of immediate manual acupuncture in the fields of sports medicine, rehabilitative medicine and recovery.

Publication date: June 16, 2021

Expiration date: June 30, 2024

Disclosure Information:

Authors have nothing to disclose.

Richard C. Niemtzow, MD, PhD, MPH, Editor-in-Chief, has nothing to disclose.

Questions:

• 1. After exercise causing diffuse muscle soreness, the immediate effects of manual acupuncture on the rate and threshold of perceived pain by algometry is?

  • A. Reduced pain perception compared to control groups

  • B. Increased pain perception compared to control groups

  • C. Reduced pain perception in both control and acupuncture groups

  • D. No differences were seen between groups

• 2. After exercise causing diffuse muscle soreness, the immediate effects of manual acupuncture on muscle activation showed?

  • A. Smaller changes than control groups

  • B. Larger changes than control groups

  • C. Large changes in both control and acupuncture groups

  • D. No differences were seen between groups

• 3. After exercise causing diffuse muscle soreness, the immediate effects of manual acupuncture on muscle force generation showed?

  • A. Small improvement in muscle force generation compared to controls

  • B. Small reduction in muscle force generation compared to controls

  • C. No improvement in muscle force generation compared to controls

  • D. Small improvement in both the control and acupuncture groups

• 4. An exercise-induced muscle damage metric might include all but which of the following?

  • A. Blood Creatine Kinase concentration

  • B. Diminished capacity to generate force

  • C. Delayed onset of muscle soreness

  • D. Blood Troponin T concentration

• 5. The acupuncture points used in this protocol were?

  • A. LI4, LI11, ST36, GB34

  • B. TH5, MH6, ST36, SP6

  • C. LI4, ST36, GB34, SP6

  • D. LI4, MH6, ST36, SP6

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