Comparison of Outcomes From Radial Extracorporeal Shock Wave Therapy Combined With Physical Therapy Versus Infrared Therapy Combined With Physical Therapy Among Patients With Myofascial Low Back Pain

Introduction

Myofascial pain syndrome (MPS) is a major contributor to chronic low back pain. Although prevalence estimates vary by setting, it affects up to 93% of patients in specialized pain management centers, substantially contributing to the burden of chronic musculoskeletal complaints [1,2]. This condition is characterized by hyperirritable spots within taut muscle bands, known as myofascial trigger points, which generate both localized and referred pain [2]. In populations with low back pain, active myofascial trigger points are present in 30% to 55% of quadratus lumborum muscles, 34% to 45% of gluteus medius muscles, and 42% of piriformis muscles; patients typically present with multiple trigger points simultaneously [1]. The pathophysiology of MPS involves complex peripheral and central mechanisms, including sustained muscle contraction, localized ischemia, algogenic substance accumulation, and progressive central sensitization [2,3]. This multifaceted pathology results in considerable functional impairment, such that patients experience clinically significant disability (mean Oswestry Disability Index [ODI] scores of 30–35 points), reduced work productivity, and diminished quality of life [4].

Current treatment approaches for low back MPS include physical therapy, manual techniques, pharmacological interventions, and thermal modalities such as infrared therapy. Physical therapy focused on core stabilization, stretching, and manual therapy constitutes the foundation of conservative management [5], although treatment outcomes remain inconsistent [6]. Among thermal modalities, infrared therapy is widely regarded as a standard adjunctive intervention to physical therapy in clinical settings due to its ease of application and low cost. Infrared therapy primarily functions through superficial thermal energy transfer, inducing vasodilation and temporary muscle relaxation. However, its role as a comparator is important: despite widespread adoption, recent evidence has led to questions about its specific efficacy beyond placebo, suggesting that this therapy provides only transient symptomatic relief without addressing the underlying pathology [7,8]. The discrepancy between robust popularity and uncertain efficacy highlights the need to rigorously compare emerging modalities (eg, radial extracorporeal shock wave therapy [rESWT]) with this established standard of care.

rESWT, a form of extracorporeal shock wave therapy (ESWT), represents a promising noninvasive treatment modality for musculoskeletal disorders. The therapeutic mechanism of rESWT involves mechanotransduction, whereby high-energy acoustic waves generate interstitial and extracellular responses that produce multiple biological effects [9,10]. Systematic reviews have demonstrated that rESWT provides efficacy comparable or superior to that of focused ESWT for various musculoskeletal conditions [11]; radial shock waves offer the advantage of treating larger tissue areas with less precise targeting requirements [12,13]. Recent prospective trials have further supported the efficacy of focused ESWT in reducing pain and improving function among individuals with chronic low back pain, providing a strong rationale for investigating shock wave interventions in the lower back [14].

For myofascial pain syndrome specifically, emerging evidence supports the therapeutic potential of rESWT. Multiple systematic reviews and meta-analyses have consistently shown that ESWT yields superior outcomes compared with control interventions, substantially reducing pain intensity and improving pressure pain thresholds across various muscle groups [15,16]. Mechanistically, ESWT appears to interrupt the self-perpetuating pain cycle in MPS by reducing peripheral nociceptor sensitivity, decreasing substance P levels, relieving sustained muscle contraction, and improving local microcirculation [17]. Thus far, most studies have evaluated ESWT as a standalone intervention or have focused on upper body regions [18]; there has been limited investigation of rESWT combined with physical therapy for low back MPS.

The rationale for combining rESWT with physical therapy lies in their complementary therapeutic mechanisms. Whereas rESWT directly addresses trigger point pathology via mechanical disruption, enhanced perfusion, and pain modulation, physical therapy targets biomechanical dysfunction, muscle imbalance, and motor control deficits that contribute to the development and persistence of MPS [19]. This multimodal approach may produce synergistic effects by simultaneously addressing both localized trigger point pathophysiology and broader musculoskeletal dysfunction. Recent evidence from acute musculoskeletal injuries suggests that combining rESWT with rehabilitation programs can accelerate recovery and improve functional outcomes relative to rehabilitation alone [20], although this combination has not been systematically evaluated for chronic low back MPS.

Despite the theoretical rationale and preliminary evidence supporting rESWT for MPS, considerable knowledge gaps remain. First, no randomized controlled studies have directly compared the combination of rESWT with physical therapy versus physical therapy with infrared therapy (a commonly used control modality) for low back MPS. Second, the clinical implications of adding rESWT to standard physical therapy protocols require quantification using validated patient-reported outcome measures. Third, the optimal integration of rESWT into multimodal rehabilitation programs for chronic low back pain associated with MPS warrants empirical validation.

Given the high prevalence of MPS in chronic low back pain and the limitations of current conservative treatments, identification of optimal nonpharmacological management strategies is critical. We hypothesized that the rESWT combination would demonstrate clinically meaningful superiority (defined as a medium effect size, Cohen’s d≥0.5) in reducing pain intensity and improving functional disability compared with the infrared combination.

Therefore, this study included patients with myofascial low back pain and aimed to compare outcomes after treatment with rESWT combined with physical therapy versus infrared therapy combined with physical therapy.

Material and Methods

ETHICAL APPROVAL:

This study was conducted in strict accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Shanghai Second Rehabilitation Hospital on July 24, 2024 (Approval No. 2024-13-01). The study protocol was registered in the institutional project management system (Project Registration No.: Y2024-07). Written informed consent was obtained from all participants prior to enrollment. Participants were fully informed of the study objectives, procedures, potential risks and benefits, and their right to withdraw at any time without consequence.

STUDY PARTICIPANTS:

Participants were recruited from patients attending the Second Rehabilitation Hospital of Shanghai between April 2024 and June 2025.

The key inclusion criterion was diagnosis of low back MPS, established according to clinical diagnostic criteria [21]. The diagnosis required simultaneous presence of all 3 essential criteria: (a) a palpable taut band in the skeletal muscle of the lumbar or pelvic region; (b) an exquisitely hypersensitive tender nodule within the taut band; and (c) reproduction of the patient’s recognized pain complaint by digital pressure on the tender nodule. Additionally, at least 1 of the following confirmatory criteria was required: (d) a local twitch response elicited by snapping palpation of the taut band; (e) painful limitation of range of motion during muscle stretching; or (f) a referred pain pattern consistent with known referral zones of the identified trigger point. All physical examinations were performed by the same experienced physician to ensure diagnostic consistency. Other inclusion criteria were as follows: (1) age between 18 and 75 years; (2) chronic low back pain for at least 3 months; (3) a baseline Numerical Rating Scale (NRS) score of 4 or greater for pain intensity; (4) cognitive ability to comply with follow-up and assessment procedures, as evidenced by a Mini-Mental State Examination score of 24 or greater; and (5) provision of informed consent to participate.

Exclusion criteria were as follows: (1) severe cardiovascular, hepatic, or renal disease; (2) history of lumbar spine surgery or invasive interventions, such as intra-articular injections, within the preceding 6 months; (3) clinically significant neurological or musculoskeletal conditions that could interfere with assessment or treatment; (4) pregnancy or breastfeeding; (5) body mass index of 30 kg/m² or greater (excluded to minimize variability in shock wave transmission due to attenuation by subcutaneous adipose tissue, and to ensure accurate manual palpation of trigger points); (6) psychiatric disorders or a Mini-Mental State Examination score below 24; and (7) withdrawal or protocol deviations that could compromise data integrity.

DROPOUT CRITERIA:

Participants were considered to have dropped out of the study if they met any of the following criteria: (1) failure to attend more than 2 consecutive treatment sessions without a valid reason; (2) withdrawal of informed consent at any time during the study; (3) noncompliance with study protocols, including failure to complete required assessments or follow-up procedures; (4) occurrence of serious adverse events related to the intervention, resulting in discontinuation of treatment; (5) development of conditions that interfered with participation, such as severe adverse reactions, major illness, or pregnancy during the study period; or (6) loss of contact with the research team or inability to attend follow-up assessments. Data analysis was conducted according to the per-protocol principle, including only participants who completed the full intervention course.

STUDY DESIGN:

This prospective, parallel-group randomized controlled trial was conducted from April 2024 to June 2025; it comprised 6 weeks of active intervention for each participant, with outcome assessments performed at baseline and after the 6-week treatment period. Participants received either physical therapy combined with infrared therapy (control group) or physical therapy combined with rESWT (experimental group). Outcome assessments, including pain intensity (NRS), disability (ODI), and patient-reported improvement (Patient Global Impression of Change [PGIC]), were performed at baseline and immediately after 6 weeks of treatment (Figure 1).

SAMPLE SIZE:

Sample size determination was performed using a 2-tailed hypothesis test with an expected medium effect size (Cohen’s d=0.5), statistical power of 80%, and significance level (α) of 0.05. Based on a preliminary pilot study conducted before the main study, calculations using G*Power 3.1 software indicated a requirement of 51 participants per group, for a total of 102 participants. Considering a potential dropout rate of 10%, the final recruitment target was set at 112 participants, who were then randomly allocated to the control and experimental groups.

GROUP ALLOCATION:

Randomization was performed using a computer-generated random number sequence stratified by sex (female vs male). Participants were assigned to either the control group (physical therapy combined with infrared therapy) or the experimental group (physical therapy combined with rESWT) after baseline assessments. Allocation concealment was achieved using opaque, sealed envelopes. Group assignment was independently verified by 2 blinded assessors. Randomization and data analysis were managed by 2 independent statisticians to minimize selection bias.

At baseline, no statistically significant differences were observed between the 2 groups in key characteristics, including age (control group: 53.25±9.68 years; experimental group: 52.88±11.60 years; P=0.853), sex distribution (control group: 55.36% women; experimental group: 51.79% women; P=0.705), NRS scores (control group: 6.07±1.64; experimental group: 6.11±1.67; P=0.909), and ODI scores (control group: 30.82±12.11; experimental group: 31.21±12.03; P=0.864). These findings confirmed that the groups were comparable at baseline (Table 1). This study used a single-blind design. Outcome assessors were blinded to group allocation to minimize detection bias; however, participants and physical therapists could not be blinded due to obvious sensory and visual differences between the rESWT and infrared interventions. To reduce potential performance bias, strict standardized treatment protocols were applied in both groups.

CONTROL GROUP:

In the control group, participants received physical therapy combined with infrared therapy. The physical therapy regimen consisted of 5 sessions per week, each lasting 30 minutes. The physical therapy program focused on core stability exercises aimed at strengthening the deep abdominal muscles and lumbar spine stabilizers. Stretching exercises were included to improve flexibility of the lumbar spine, hip flexors, and hamstrings; postural correction exercises were implemented to promote proper alignment of the pelvis and lumbar spine during daily activities. Manual therapy techniques, including soft tissue mobilization and joint mobilization, were incorporated to alleviate pain and improve range of motion in the lumbar region.

In addition to physical therapy, participants in the control group received infrared therapy twice weekly; each session lasted 15 minutes. Treatment was delivered using the YSHT-II infrared thermal radiation therapy lamp (Shanghai Yuejin Medical Optical Instruments Factory, Shanghai, China; input power: 400 W). The lamp was positioned approximately 40 cm from the skin surface and directed at the lumbar and pelvic regions where participants reported pain.

EXPERIMENTAL GROUP:

In the experimental group, participants received the same physical therapy regimen (5 sessions per week, each lasting 30 minutes). Exercises were identical to those used in the control group (eg, core stability, stretching, postural correction, and manual therapy). These interventions were intended to reduce pain, improve function, and enhance mobility in the lumbar region.

In addition to physical therapy, participants in the experimental group received rESWT twice weekly; each session lasted 10 to 15 minutes. Treatment was administered using the Swiss DolorClast device (Electro Medical Systems S.A., Nyon, Switzerland) equipped with a 15-mm applicator. The energy level was set at 2.0 to 2.5 bar with a frequency of 5 to 10 Hz, and 2000 pulses were delivered in each session. Ultrasound gel was used as a coupling medium. Shock waves were applied to painful trigger points in the lumbar region, including the erector spinae and iliopsoas muscles, using a sweeping motion to ensure even distribution. Care was taken to avoid direct application to bony structures.

ASSESSMENT TOOLS:

Primary outcome measures in this study were pain intensity, functional disability, and patient-reported improvement, assessed using the NRS, ODI, and PGIC. All outcome measures were self-reported by the participants under the guidance of a research assistant who was blinded to group allocation.

NUMERICAL RATING SCALE: Pain intensity was evaluated using the NRS, a validated and commonly used tool for assessing pain severity [22]. Participants were asked to rate their current pain level on an 11-point scale from 0 (no pain) to 10 (worst imaginable pain). Higher scores indicate greater pain intensity. The NRS was assessed at baseline and after 6 weeks of treatment.

OSWESTRY DISABILITY INDEX: Functional disability was assessed using the ODI, a widely used self-administered questionnaire designed to measure the degree of disability caused by low back pain [23]. The ODI consists of 10 items that assess pain intensity, personal care, lifting, walking, sitting, standing, sleeping, sex life, social life, and traveling. Each item is scored from 0 to 5, and the total score is expressed as a percentage (0–100%); higher scores indicate greater disability. Participants completed the ODI at baseline and after 6 weeks of treatment.

PATIENT GLOBAL IMPRESSION OF CHANGE:

Patient-reported improvement was assessed via the PGIC, which asks participants to rate their overall perception of improvement or deterioration in their condition [24]. The PGIC uses a 7-point Likert scale; scores range from 1 (very much improved) to 7 (very much worse). Lower scores indicate greater perceived improvement. This tool was used to assess participants’ perception of treatment effectiveness at the end of the 6-week treatment period.

STATISTICAL ANALYSIS:

Data analysis was performed using SPSS version 26.0 (IBM Corp., Armonk, NY, USA) and GraphPad Prism version 10.6 (GraphPad Software, San Diego, CA, USA). Continuous outcomes, including NRS, ODI, and PGIC scores, were expressed as mean±standard deviation. Regarding attrition, 7 participants dropped out (4 in the control group and 3 in the experimental group). To ensure that the study remained adequately powered, these participants were replaced by recruiting new eligible individuals to maintain the target sample size of 112. Consequently, data analysis followed the per-protocol principle. Given the sample size of 56 per group, parametric tests were considered appropriate based on the central limit theorem. Between-group differences in changes from baseline to the 6-week follow-up were assessed with independent-samples t-tests. Within-group changes were analyzed using paired-samples t-tests. Categorical variables were compared via Pearson chi-square tests. GraphPad Prism software was used for data visualization.

Effect sizes for all t-tests were calculated using Cohen’s d to provide a measure of the clinical significance of the observed changes. All statistical tests were 2-sided. To control for Type I error inflation due to multiple primary endpoints (NRS, ODI, and PGIC), Bonferroni correction was applied, adjusting the significance threshold to α=0.017 (0.05/3).

Results

PARTICIPANT FLOW AND BASELINE CHARACTERISTICS:

In total, 119 participants were initially enrolled and randomized. During the intervention phase, 7 participants (4 in the control group and 3 in the experimental group) discontinued the study for personal reasons. Consequently, 112 participants completed the full protocol and were included in the final analysis: 56 in the control group and 56 in the experimental group. Baseline demographic and clinical characteristics were well balanced between the 2 groups (Table 1).

GROUP COMPARISON RESULTS:

In the control group, paired t-tests were conducted to evaluate changes in NRS and ODI scores from baseline to the 6-week follow-up. The analysis revealed no significant changes in either outcome. Specifically, the NRS score showed a slight reduction from 6.07±1.64 at baseline to 5.95±1.59 at the 6-week follow-up, with a mean difference of 0.13 (95% confidence interval [CI]: −0.052 to 0.302; t=1.412, P=0.163), which was not statistically significant. The ODI score marginally decreased from 30.82±12.11 at baseline to 29.98±12.69 at the 6-week follow-up, with a mean difference of 0.84 (95% CI: −0.632 to 2.310; t=1.143, P=0.258), which also did not demonstrate statistical significance.

Effect sizes for the changes in NRS and ODI scores were calculated using Cohen’s d. For the NRS score, Cohen’s d was 0.189, indicating a very small effect size. For the ODI score, Cohen’s d was 0.153, suggesting a negligible effect.

In contrast, the experimental group showed statistically significant improvements in both NRS and ODI scores after 6 weeks of treatment. The NRS score decreased from 6.11±1.67 at baseline to 5.43±1.82 at the 6-week follow-up, with a mean difference of 0.68 (95% CI: 0.461–0.896; t=6.258, P<0.01). Similarly, the ODI score decreased from 31.21±12.03 at baseline to 25.93±13.98 at the 6-week follow-up, with a mean difference of 5.29 (95% CI: 3.756 to 6.816; t=6.923, P<0.01).

Effect sizes in the experimental group also were substantial. Cohen’s d for the NRS score was 0.836, indicating a moderate effect size. For the ODI score, Cohen’s d was 0.925, also indicating a moderate effect size (Table 2).

BETWEEN-GROUP COMPARISON RESULTS:

Between-group comparisons were performed to assess differences in changes from baseline to the 6-week follow-up between the control and experimental groups. The results revealed significant differences in all primary outcomes: PGIC, NRS, and ODI (Figure 2).

For the PGIC, the experimental group showed significantly greater improvement than the control group. The mean PGIC score in the control group was 4.07±1.36, whereas the experimental group reported a mean score of 2.82±1.53. The mean difference between groups was 1.25 (95% CI: 0.71 to 1.79), with a t-value of 4.575 (P<0.0001) and Cohen’s d of 0.865. To assess clinical significance, responders were defined as participants achieving a PGIC score of 2 or less (“much improved” or “very much improved”). The experimental group demonstrated a significantly higher responder rate (44.6%, n=25) compared with the control group (10.7%, n=6), representing a statistically significant difference (χ²=15.96, P<0.01).

The NRS score showed a significantly greater reduction in the experimental group than in the control group. The control group exhibited a mean change of 0.13±0.66, whereas the experimental group showed a mean change of 0.68±0.81. The mean difference between groups was 0.55 (95% CI: 0.28 to 0.83), with a t-value of −3.955 (P<0.001) and Cohen’s d of 0.747.

The ODI score also decreased significantly more in the experimental group. The control group exhibited a mean change of 0.84±5.49, whereas the experimental group showed a mean change of 5.29±5.71. The mean difference between groups was 4.45 (95% CI: 2.35 to 6.55), with a t-value of −4.198 (P<0.0001) and Cohen’s d of 0.793 (Table 3).

Discussion

This randomized controlled trial provides evidence that combining rESWT with physical therapy yields clinically meaningful improvements in pain, functional disability, and patient-reported outcomes among patients with low back MPS, relative to physical therapy combined with infrared therapy. The experimental group demonstrated moderate-to-large effect sizes across all primary outcomes (Cohen’s d=0.747–0.865). However, regarding absolute clinical relevance, we acknowledge that the between-group difference in NRS (0.55 points) did not exceed the commonly cited minimal clinically important difference threshold of 1.5 to 2.0 points for chronic pain. This discrepancy suggests that, although rESWT provides a consistent statistical benefit at the population level, the additional magnitude of pain relief for an individual patient may be modest. Nevertheless, the significantly higher responder rate (PGIC ≤2) in the rESWT group (44.6% vs 10.7%) indicates that, for some patients, the intervention yields perceptible and clinically meaningful benefits.

Our findings are consistent with the most comprehensive meta-analytic evidence on ESWT for chronic low back pain. In a 2023 systematic review and meta-analysis of 12 randomized controlled trials involving 632 patients, Liu et al demonstrated that ESWT provided significantly greater pain relief than control interventions at both 4 weeks (weighted mean difference [WMD]=−1.04; 95% CI=−1.44 to −0.65; P<0.01) and 12 weeks (WMD=−0.85; 95% CI=−1.30 to −0.41; P<0.01). Similarly, functional disability measured by ODI showed significant improvement in the ESWT group at 4 weeks (WMD=−4.22; P<0.01) and 12 weeks (WMD=−4.51; P=0.03) [25]. Our observed between-group differences in NRS (0.55 points) and ODI (4.45 points) fall within these meta-analytic estimates, confirming consistency with the broader evidence base and suggesting that our treatment protocol achieved effects comparable to pooled international data. Our results also align with recent findings by Ogbeivor et al [18], who reported positive outcomes for myofascial pain. However, the present study differs in that it specifically demonstrates the additive benefit of rESWT over a standardized active thermal control.

The importance of long-term follow-up in evaluating rESWT efficacy was highlighted in the 2019 prospective randomized single-blind trial conducted by Walewicz et al, which demonstrated that the analgesic effects of rESWT became more pronounced during extended observation [19]. In that study of patients with chronic low back pain, the rESWT group showed progressive improvement from the immediate post-treatment period through the 3-month follow-up, with Visual Analog Scale scores decreasing from 4.6 at 1 week to 2.0 at 3 months (P<0.01), whereas the sham group’s pain increased from 3.5 to 4.4 over the same period [19]. This pattern of sustained and progressive benefit contrasts with our 6-week assessment time point, suggesting that the present study might have underestimated the full therapeutic potential of rESWT by not extending follow-up beyond the active treatment phase.

However, a critical gap in the current literature is the absence of long-term efficacy data. In a 2024 systematic review of focused ESWT for low back pain, Ferdinandov identified only 3 randomized controlled trials (94 patients total) that met the inclusion criteria; pain levels at 3 months no longer showed statistically significant differences between groups, and none of the studies included follow-up beyond this time point [26]. This consistent lack of extended follow-up represents a major limitation in the field, preventing definitive conclusions about whether ESWT produces lasting structural changes or primarily provides temporary symptomatic relief that diminishes after treatment cessation.

Comparison with pharmacological interventions provides additional context for interpreting the present findings. In a 2021 randomized trial comparing rESWT, rESWT combined with celecoxib and eperisone, and celecoxib and eperisone alone in 140 patients with chronic nonspecific low back pain, Guo et al demonstrated that rESWT was not inferior to standard pharmacological treatment in a Chinese population [27]. At the 12-week follow-up, all 3 groups showed statistically significant improvement over time; rESWT displayed efficacy comparable to that of pharmaceutical therapy while avoiding medication-related adverse effects. These findings suggest that rESWT represents a viable nonpharmacological alternative, with the potential to reduce reliance on nonsteroidal anti-inflammatory drugs (NSAIDs) and muscle relaxants, which are associated with gastrointestinal, cardiovascular, and hepatorenal risks during long-term use.

The minimal improvement observed in our infrared control group (NRS reduction 0.13 points, P=0.163; ODI reduction 0.84 points, P=0.258) is consistent with the limited evidence supporting infrared therapy for musculoskeletal pain. To our knowledge, there are no recent high-quality cost-effectiveness analyses specifically comparing rESWT with infrared therapy; however, the economic burden of musculoskeletal disorders provides relevant context. In a 2013 analysis of National Health Interview Survey data (2004–2010, n=185 829 adults), Dall et al estimated that musculoskeletal disorders were responsible for $510 billion in direct medical expenditures and $339 billion in lost productivity annually in the United States [28]. In this context, interventions that reduce pain and improve function may generate substantial societal economic benefits through improved work participation and reduced disability payments, although formal cost-utility analyses are required to quantify the specific economic value of rESWT.

The comparative efficacy of rESWT versus other trigger point interventions, particularly dry needling, also merits consideration. A randomized trial by Luan et al revealed no significant differences in pain relief or functional improvement between rESWT and dry needling for myofascial trigger points [29]. This finding is consistent with systematic reviews suggesting that, although dry needling is effective, it does not demonstrate clear superiority over rESWT [30,31]. Given this apparent therapeutic equivalence, treatment selection should consider patient preference and safety profile; rESWT provides a noninvasive alternative for patients with needle phobia or contraindications to invasive procedures, offering a practical clinical advantage despite similar efficacy outcomes.

An additional advantage of rESWT is its favorable safety profile. In a 2020 comprehensive update on ESWT, Auersperg and Trieb concluded that it is a safe treatment with few known side effects, most commonly pain during treatment and minor hematomas; severe complications are not expected when the procedure is performed following recommended guidelines [32]. Reported contraindications include severe coagulopathy for high-energy ESWT, treatment directed toward the fetus or embryo, and the presence of severe infection. In a 2017 systematic review examining complications of ESWT in the treatment of plantar fasciitis (39 studies, 2493 patients, 6424–6497 treatment sessions), Roerdink et al also found that ESWT was likely to be safe; no complications were reported at the 1-year follow-up, although long-term complications beyond this time point remain uncertain due to the absence of extended surveillance data [33]. Common transient adverse effects included temporary pain increase, swelling, erythema, petechiae, and small hematomas, which typically resolved before subsequent treatment sessions.

This safety profile compares favorably with pharmacological alternatives. NSAIDs carry risks of gastrointestinal bleeding, cardiovascular events, and renal impairment, particularly during prolonged use in older adults and patients with comorbidities. Muscle relaxants may cause sedation, dizziness, and cognitive impairment that can affect work performance and driving safety. Opioid analgesics present risks of dependence and respiratory depression; they also contribute to the ongoing opioid epidemic. Trigger point injections, whether with local anesthetic or corticosteroid, involve procedural risks such as infection, bleeding, pneumothorax (for thoracic locations), and – with corticosteroids – potential tendon weakening or rupture upon repeated administration. Against this background of therapeutic alternatives with substantial adverse-effect profiles, the rESWT-related transient local discomfort and minor soft-tissue reactions represent a meaningful safety advantage.

Clinical factors requiring consideration in ESWT application include current use of NSAIDs or anticoagulants, recent corticosteroid injections, and the presence of cardiac pacemakers or other implantable devices. Although coagulopathy is cited as a contraindication in the International Society for Medical Shockwave Treatment 2019 guidelines, patients receiving such treatment typically are excluded from research studies, making safety evaluation difficult in this population [32]. The International Society for Medical Shockwave Treatment guidelines recommend an energy flux density of 0.10 to 0.32 mJ/mm2 for various musculoskeletal conditions, with parameters adjusted according to patient pain tolerance and tissue depth. Our protocol (2.0–2.5 bar, 5–10 Hz, 2000 pulses) falls within these recommended ranges, supporting the generalizability and safety of the present approach.

Although the precise biological pathways underlying the effects of rESWT in MPS have not been fully elucidated, existing basic science evidence supports several key mechanisms. Experimental studies have shown that shock waves stimulate neovascularization and upregulate angiogenic growth factors in ischemic tissues. In the context of MPS, these physiological changes may help reverse the local ischemia-hypoxia cycle characteristic of myofascial trigger points, addressing the underlying energy deficit. Furthermore, the immediate pain relief observed in the present study is likely mediated by hyperstimulation analgesia and disruption of sensory nerve impulse transmission, as suggested by previous neurophysiological findings. Interventions that modulate muscle function (eg, intramuscular electrical stimulation) have also demonstrated beneficial effects on multifidus muscle properties in patients with chronic low back pain [34]. We hypothesize that the combination of rESWT with physical therapy provides synergistic benefits, where rESWT primarily targets microscopic physiological abnormalities and physical therapy corrects macroscopic biomechanical dysfunction.

Peripherally, mechanical stimulation of large-diameter mechanoreceptive fibers may activate descending inhibitory pathways via gate-control mechanisms. Centrally, repeated noxious stimulation might trigger counterregulatory responses, including endogenous opioid release and modulation of central sensitization. The biochemical effects of shock waves on nociceptor sensitivity and neurotransmitter expression represent additional potential mechanisms that require further investigation in controlled laboratory studies.

These findings have several practical implications for the management of chronic low back MPS. First, rESWT combined with physical therapy represents an evidence-based treatment escalation option for patients with an inadequate response to conventional physical therapy and thermal modalities. The moderate-to-large effect sizes (Cohen’s d=0.747–0.865) indicate clinically relevant improvement; however, the modest absolute between-group differences (NRS 0.55 points, ODI 4.45 points) suggest that benefits gradually accumulate and may require more than 6 weeks of treatment to achieve changes that exceed minimal clinically important difference thresholds.

Second, the protocol used in this study (2000 pulses per session, energy level 2.0–2.5 bar, frequency 5–10 Hz, twice weekly for 6 weeks) provides a reproducible framework that falls within international guideline recommendations and demonstrated acceptable safety in our cohort. Clinicians implementing rESWT should consider that optimal parameters may require individualization according to patient pain tolerance, tissue depth, and specific anatomical factors.

Third, the absence of statistically significant improvement with infrared therapy in the control group, despite its frequent use in clinical practice, raises questions about routine use of this modality for MPS. Clinical resources may be more effectively allocated to interventions with established efficacy or to increasing the frequency and duration of physical therapy. The comparable efficacy of rESWT and dry needling suggests that patient preference, contraindications, and practitioner expertise should guide selection between these trigger-point-targeted interventions.

Fourth, the apparent greater effectiveness of rESWT in chronic rather than acute conditions suggests that the timing of treatment initiation is important. Early aggressive use of rESWT for acute low back pain is not supported by current evidence; delayed initiation after chronicity develops may involve the treatment of more established pathological changes that are less responsive to therapy. The optimal timing for introduction of rESWT during the natural course of low back pain requires prospective investigation.

Finally, the favorable safety profile and absence of serious adverse events reported in large systematic reviews support the use of rESWT as a low-risk intervention appropriate for outpatient rehabilitation settings. The transient and self-limited nature of reported adverse effects, in addition to the absence of systemic complications, compares favorably with pharmacological alternatives, particularly for patients requiring long-term pain management or those with contraindications to medication.

Several limitations should be acknowledged. First, the single-blind design introduces potential performance and detection bias. Although outcome assessors were blinded, the lack of participant and therapist blinding – due to obvious sensory differences between interventions – remains a limitation that may affect patient-reported outcomes. Second, the 6-week follow-up period precludes evaluation of long-term efficacy. Given the chronic nature of MPS, future studies should explore whether the observed benefits persist beyond the immediate treatment phase. Third, objective trigger point assessment tools were not used, and participants were not stratified according to trigger point characteristics, thus limiting mechanistic insight into specific pathological changes. Fourth, strict inclusion criteria – particularly exclusion of individuals with body mass index 30 kg/m2 or greater to ensure consistent shock wave transmission – hinder generalizability to obese populations and to patients with severe refractory conditions. Fifth, the use of infrared therapy as the active control prevents direct comparison with other evidence-based interventions, such as dry needling. Finally, missing data were handled by replacing dropouts to maintain the target sample size, resulting in a per-protocol analysis rather than intention-to-treat analysis; although this approach preserved statistical power, it may have introduced selection bias favoring participants who completed the study.

Conclusions

Compared with infrared therapy plus physical therapy, rESWT plus physical therapy yielded greater improvements in pain and disability. These findings support use of rESWT for the management of chronic low back MPS.