Abbreviations

NRS: Numeric Rating Scale

MCID: Minimal Clinically Significant Difference

EMF: Electromagnetic Field

PEMF: Pulsed Electromagnetic Field

1. Introduction

Chronic musculoskeletal pain is a global health issue, affecting over 1.7 billion people, including 619 million with low back pain, a leading cause of disability [1]. One in five adults in many countries reports pain for over three months, limiting mobility, lowering quality of life, and increasing socioeconomic burdens through lost productivity and healthcare costs. Its prevalence rises with age and often persists into work years. Retail workers are at high risk due to long-standing hours and repetitive tasks, with 30% to over 60% experiencing upper extremity and back pain annually, and nearly 90% reporting neck or back discomfort [2]. Factors like repetitive motions, heavy lifting, long standing, and awkward postures contribute to these disorders [3].

Existing treatments for chronic musculoskeletal pain such as NSAIDs, opioids or non-drug methods are often inadequate. Electromagnetic field (EMF) therapies, including static magnetic therapy and pulsed electromagnetic field (PEMF) therapy, offer alternative options for treating musculoskeletal pain [4,5]. Static magnets are claimed to relieve pain, but evidence is limited and meta-analyses show no significant pain reduction compared to a placebo [4]. On the other hand, PEMF therapy has shown some promising results, reducing pain and improving function in conditions like knee osteoarthritis, shoulder impingement, neck pain, back pain, fibromyalgia, and plantar fasciitis [6]. Although the evidence is mixed and studies are small, these findings suggest that time-varying EM fields may have therapeutic potential for painful joints and soft tissues.

Preclinical studies have demonstrated biological effects of this field configuration, including a 39.9% increase in fibroblast migration and a 24% reduction in endogenous oxygen radicals, suggesting regenerative and antioxidative properties [7]. Besides these cellular effects, the technology is designed to support modulation of nociceptive signaling and circulation during daily use without requiring an external power source. We, therefore, conducted a prospective, double-blind, randomized controlled trial with retail workers suffering from chronic musculoskeletal pain to determine whether daily use of the Powerinsole® device for 40 days reduces pain more effectively than a placebo. The trial also evaluated functional outcomes, analgesic use, and patient acceptance.

2. Material and Methods

2.1. Powerinsole® device

The Powerinsole® is a wearable device based on innovative technology, featuring precisely aligned permanent magnets mounted on a flexible printed circuit board (FPC, Figure 1). This setup creates a complex, spatially varied magnetic field characterized by overlapping strengths and directions. The field structure displays a multipolar magnetic pattern like natural physiological cell communication processes, potentially affecting ion transport (primarily calcium and sodium ions), neuronal excitability, and microcirculation.

2.2.Trial design and participants

Randomization and blinding: Participants were randomized 1:1 using computer-generated block randomization. Allocation concealment was ensured with opaque, sealed envelopes prepared by an independent staff member not involved in enrollment or data collection. Both participants and outcome assessors were blinded to allocation throughout; at study end, allocation guesses were within chance levels, indicating successful blinding.

By following the CONSORT guidelines, this investigation was conducted as a prospective, double-masked, placebo-controlled, crossover application trial. The total trial duration was 40 days, during which participants were randomized in a 1:1 allocation to either the active Powerinsole® or a visually identical placebo Powerinsole® device. Group A received the active intervention for the entire trial period, and Group B initially received the placebo for 20 days and was then switched to the active product from Day 21 onward. Follow-up assessments were conducted at Days 10, 20, 30, and 40.

A total of 117 retail employees (72 female, 45 male) were enrolled, with a mean age of 43.2 years (range, 19-68 years). All participants were engaged in physically demanding tasks, including shelf stocking, cashiering, and warehouse work. Inclusion criteria required adults aged 18-68 years with chronic pain lasting longer than three months and a baseline pain intensity score of 4 or greater on a 0-10 Numeric Rating Scale (NRS). Exclusion criteria included pregnancy or breastfeeding, implanted electronic devices such as pacemakers, active drug or alcohol abuse, and participation in other pain studies within the previous three months.

Participants wore the device for ≥ 4 hours/day. The placebo unit was externally identical and applied in the same manner, but did not contain the polymorphic magnetic array.

The trial maintained rigorous blinding procedures, with both participants and investigators unaware of treatment allocation. Intervention protocols required daily use of the Powerinsole® device for a minimum of 4 hours. Participants could wear the Powerinsole® inside their everyday shoes (for foot and heel pain, with the magnetic side facing upward) or apply it directly to painful sites such as the back, shoulders, or knees using skin-friendly medical tape (e.g. kinesiology tape; Figure 2). Device placement was tailored to each participant’s symptoms, and self-application was supported through written instructions and an instructional video.

2.3. Endpoints and assessments

The primary efficacy endpoint was the change in pain intensity (0-10 NRS) from Day 0 to Day 20. Pain was assessed by asking “How intense is your pain right now?” on each survey. Secondary endpoints included proportion of participants achieving a clinically meaningful improvement (defined a priori as ≥ 2 point drop in NRS, consistent with published MCID thresholds [8,9], patient-reported function, changes in analgesic medication use, and safety/acceptability measures including side effects, comfort, satisfaction, and willingness to continue. Questionnaires were administered at baseline (Day 0) and at Days 10, 20, 30, and 40 via an online platform; response rates exceeded 95% at each time point.

3. Statistical Analysis

A priori sample size calculations assumed a between-group difference of 2.0 NRS points (SD 2.5) with two-sided α = 0.05 and 80% power, requiring ≥ 52 participants per arm at Day 20; with N = 117 randomized, the trial was adequately powered for the primary endpoint.

Analyses followed an intention-to-treat principle. Continuous outcomes (e.g. pain scores) were summarized by group as means ± standard deviations and compared using mixed-effects linear models with group, time, and group-by-time interaction terms, adjusting for baseline score. A p < 0.05 (two-sided) was considered significant. Missing data were infrequent; outcomes were analyzed using all available data.

4. Results

4.1. Baseline characteristics

A total of 117 participants (72 women, 45 men; mean age 43.2 years, range 19-68) were randomized (Group A n = 58; Group B n = 59). The two groups were similar in baseline demographics and pain metrics. Baseline pain intensity averaged about 5.3 ± 1.3 on a 0-10 numeric rating scale (NRS) in both groups, with no significant difference. Pain was chronic and spread across the targeted regions: about one-third reported low-back pain (~ 33%), nearly half had foot or heel pain (~ 44%), with smaller groups reporting neck pain (Group A 16% vs Group B 3%) or shoulder pain (2% vs 15%), and a few had knee pain (7% vs 0%). 

The qualitative nature of pain varied but showed some imbalance between groups: for example, “stabbing” pain was endorsed by 61% in Group A vs 83% in Group B, whereas “pulling” pain was more common in Group A (63% vs 17%). Despite these minor differences in pain descriptors, overall baseline pain severity and interference were similar between groups (Table 1).

4.2. Treatment exposure and compliance

Over 90% of participants in both groups reported wearing the Powerinsole® device for at least 4-8 hours/day on most days. There was no significant difference in adherence between groups. Use of concomitant pain medications was permitted; similar proportions in each group used occasional analgesics at baseline.

 4.3. Primary endpoint: pain intensity outcomes

By Day 20, after the double-masked phase, the active treatment group demonstrated a reduction in pain compared to the placebo. Group A’s mean pain score improved from approximately 5.3 at baseline to 3.6 on Day 20, while Group B remained essentially unchanged (mean approximately 5.8 after placebo). The difference in pain intensity between groups at 20 days was -2.21 NRS, 95% CI -2.79 to -1.63; p < 0.001. Work interference also favored the active group -2.53 NRS, 95% CI -3.06 to -2.00; p < 0.001. MCID responder rates at Day 20 were higher with active treatment compared to placebo (61.5% [32/52] vs 1.9% [1/54]; p < 0.001) (Figure 3).

4.4. Responder analysis

The proportion of participants achieving a clinically significant improvement in pain (≥ 2 points NRS reduction) by Day 20 was dramatically higher in Group A (61.5%) than in Group B (1.9%), as shown in Figure 4. In practical terms, virtually none of the placebo-treated subjects reached the minimal clinically significant difference (MCID) at 20 days, versus well over half of those receiving active treatment (p < 0.001).

4.5. Crossover phase and longitudinal outcomes to 40 Days

After the placebo group crossed over to active treatment at Day 21, and both groups were on active treatment, their pain scores began to improve for Group B. By Day 30 (10 days into crossover), Group B’s mean pain had decreased to approximately 4.1. Group A, continuing active treatment, maintained their improvements with a mean pain score of about 2.6 at Day 40. By Day 40, the differences had narrowed but still favored the initially active group for pain, with a mean pain score of 2.8 versus 3.7 in Group B -0.86, 95% CI -1.44 to -0.29; p = 0.004; d = 0.5, and work interference of −0.84, 95% CI -1.48 to -0.19; p = 0.012; d = 0.7. Day-40 responder rates were similar at 66.7% [38/57] versus 59.3% [32/54]; p = 0.42 (Fig. 3. D, C).

Notably, once Group B received the active Powerinsole® device, their rate of pain responders also increased significantly, 66.7% [38/57] vs 59.3% [32/54]; p = 0.42. By Day 40, 59% of the original Group B had achieved ≥ 2-point improvements, nearly matching the 67% responder rate in Group A (difference 7%, p = 0.42). In other words, the pain relief observed at 3 weeks in Group A was also seen in Group B after they received the device, supporting an analgesic effect rather than a permanent difference between groups. There were no significant interactions between treatment and baseline subgroups (e.g. similar relative benefits across different pain sites and demographics), supporting the consistent efficacy of the device.

4.6. Secondary outcomes: sleep, mood, quality of life, and walkability

Across secondary outcomes, consistent patterns emerged that further supported the effectiveness of the Powerinsole® intervention. As shown in Figure 5, for sleep, both groups reported moderate impairment at baseline (NRS ~3-4/10). Group A (active device from Day 0) showed steady improvement over the 40 days, while Group B (placebo until Day 20) experienced a temporary worsening during the placebo phase, peaking at Day 20. After switching to the active device, Group B’s sleep outcomes improved significantly, catching up to Group A by Day 40. Mood trends demonstrated a similar pattern. Group A improved steadily from baseline, with improvements maintained through Day 40. Conversely, Group B stayed more impaired while on placebo, then improved quickly after switching to the active device, reaching similar levels as Group A by the end of the trial. Quality of life results followed the same trend: Group A continued to improve across all time points, while Group B showed little to no benefit under placebo, and sometimes worsened, until crossover at Day 21. Afterward, their scores improved and matched Group A by Day 40. Finally, walkability steadily increased in Group A over the trial period, with significant functional gains reported by Day 40. Group B’s walkability scores remained unchanged during the placebo phase but improved significantly after crossover, again aligning with Group A by the end of the trial. Overall, these findings suggest that, alongside pain reduction, the Powerinsole® device delivered broader benefits across sleep, mood, quality of life, and physical function, with effects only appearing under active treatment and converging after crossover.

5. Safety and acceptability

The Powerinsole® device was well tolerated, with no serious adverse events reported throughout the 40-day trial. Only one participant (0.9%) described a mild, transient side effect in this case, localized skin irritation. No other device-related complaints emerged. On the contrary, user feedback at trial conclusion was overwhelmingly positive (Table 2). Participants rated the Powerinsole® device as highly comfortable to wear with a mean comfort score of 4.3 ± 0.9 on a 5-point scale, with 86% rating comfort as “good” or “excellent”. Ease of use was nearly unanimously praised, with 96% finding daily use “easy” or “very easy” (mean ease score 4.8 ± 0.7).

Overall satisfaction was high (mean 4.3 ± 0.9, with 83% “satisfied” or “very satisfied”). Accordingly, 91.5% of all participants stated they would recommend the Powerinsole® to others, and 96.6% said they intended to continue using it beyond the trial. There were no notable differences in these acceptability measures between the originally active vs placebo groups after both had experienced the device. In summary, the intervention demonstrated an excellent safety profile and strong user acceptance, suggesting it can be readily integrated into daily life without comfort or compliance issues.

6. Discussion and Conclusion

Existing treatments for chronic musculoskeletal pain such as NSAIDs, opioids or non-drug methods are often inadequate. NSAIDs and opioids offer temporary relief but carry risks [10]. Long-term NSAID use can cause serious health issues. Non-drug methods like physical therapy, exercise, and cognitive-behavioral therapy are recommended, but many patients still suffer persistent pain and disability [11-13]. Exercise and rehabilitation improve function modestly, but require ongoing effort. Many patients experience only partial relief from pharmacological treatments and face adverse effects that limit dosage. Overall, no treatment reliably provides long-term relief, highlighting the need for complementary approaches such as pulsed or static electromagnetic devices [4,5].

Several theories exist how magnetic fields reduce pain. Magnetic fields influence nerve activity and pain signaling, possibly altering the excitability of peripheral nociceptors by shifting the resting membrane potential to increase their activation threshold [14]. Magnetotherapy could enhance microcirculation and tissue perfusion, delivering more oxygen and nutrients for healing [15]. At the cellular level, PEMF stimulation may induce currents that disrupt cell membranes, activate pathways, and upregulate growth factors like FGF-2, promoting angiogenesis and speeding wound repair [16]. Clinical evidence shows static magnetic insoles reduce pain over weeks, likely penetrating up to 20 mm to reach nociceptors, and studies indicate decreased oxidative stress and faster fibroblast migration, supporting tissue repair [17]. Overall, wearable magnetic devices might provide neuromodulation and circulation improvements to relieve pain without drugs [18]. In the present trial, mechanistic endpoints were not measured; mechanistic interpretations are therefore hypothetical and based on prior preclinical literature.

In this trial, retail workers using the Powerinsole® technology experienced significantly greater pain relief compared to those using a placebo version of the device. The active intervention resulted in an average 3-point reduction in NRS pain over 40 days, surpassing the commonly cited MCID of approximately 2-3 points. In contrast, pain reduction in the placebo group was more modest. Correspondingly, a substantially higher proportion of participants receiving the active treatment achieved a ≥ 2-point improvement. These findings indicate a genuine analgesic effect of the wearable polymorphic magnetic field device beyond placebo.

The pain improvement trajectory shows that the effect appeared by Day 10 and was sustained through Day 40. By day 40, groups experienced some early improvement, consistent with a placebo response; however, the active group continued to improve steadily. Patient-reported outcomes, including function and satisfaction, reflected the pain results, with enhanced activity in 67% of the active group compared to 31% of the placebo group. Importantly, no safety concerns arose; all participants tolerated the device without issues. Acceptability was excellent, with over 96.6% willing to continue use and more than 91.1% recommending it, indicating high ratings for comfort and ease of use.

These results support previous research on non-drug pain treatments. For instance, a trial of a topical micro/nanotechnology patch showed significant pain score reductions [19]. Our trial builds on this by showing the effectiveness of a wearable polymorphic magnetic field device in a strict double-blind randomized controlled trial. The retail worker group was specifically selected because of chronic pain from prolonged standing; while the results might apply to other pain groups, they need to be confirmed with broader patient samples. Effect sizes observed here are comparable to those reported for selected non-pharmacological approaches, and while findings may generalize beyond retail workers, confirmation in broader populations is warranted.

The trial relied on self-reported outcomes without objective functional testing. About 5% of survey non-responses might introduce bias, although completion rates were high. Adherence could only be estimated through self-report. Participant matching across survey waves was not perfect; however, analyses based on randomized assignment (Group A vs B) ensured robustness. The relatively short follow-up period of 40 days does not offer insight into long-term durability. Lastly, while the placebo was visually identical, subtle differences could have unblinded some users; nonetheless, the significant difference in pain outcomes indicates a genuine treatment effect beyond expectations. In addition, no washout period was included between phases in the crossover; although carryover effects cannot be fully excluded, the post-crossover improvement in Group B mirrored early changes in Group A, suggesting minimal carryover under the protocol.

Larger trials with objective functional measures, longer follow-up periods, and more diverse populations are needed. Mechanistic studies (e.g. neuroimaging or biomarkers) could help clarify how polymorphic magnetic fields create analgesic effects. Exploring optimal daily wear times and potential synergy with physiotherapy or exercise may also prove beneficial.

In conclusion, the use of a novel wearable polymorphic magnetic field technology device named Powerinsole® significantly alleviated chronic musculoskeletal pain in retail workers compared to a placebo, with most participants reporting clinically meaningful benefits. The device was safe, well-tolerated, and highly acceptable. These findings support further development of polymorphic magnetic field therapies as part of multimodal pain management strategies.

7. Acknowledgements

The authors thank Lidl Österreich GmbH, Betriebsrat, Unter der Leiten 11, A-5020 Salzburg, Austria, for their kind support and the opportunity to conduct this trial.

8. Conflict of Interest

The study was supported logistically by Lidl Österreich GmbH. Prof. Dr. Dartsch served as a scientific consultant but had no role in data collection. Data analysis and interpretation were conducted independently.

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