Abstract Latent myofascial trigger point (MTrP) pain is commonly managed with manual techniques and heat therapy. To enhance therapeutic convenience and efficacy, a cordless heat-assisted massage device was developed by integrating mechanical massage with superficial heat application. This pilot randomized controlled crossover trial was conducted in 20 female participants with latent MTrPs of the upper trapezius muscle. Each participant received two conditions in random order: (1) massage with the cordless heat-assisted device with heating activated and (2) sham massage with the device without heating, separated by a 24–48 hour washout period. Each intervention lasted 10 minutes. Skin temperature, tissue blood flow, and pressure pain threshold (PPT) were assessed at baseline, immediately after treatment, and 5 minutes post-treatment. Data were analyzed using two-way repeated measures ANOVA. The treatment condition significantly increased skin temperature (P < 0.01) and tissue blood flow (P < 0.001) compared with baseline. Furthermore, increases in skin temperature (P < 0.01) and tissue blood flow (P < 0.05) were significantly greater in the treatment condition than in the sham condition.  However, no significant changes in pressure pain threshold were observed across conditions (P > 0.05). This study suggests that the cordless heat-assisted massage device effectively increased skin temperature and enhanced tissue blood flow at latent MTrP of the upper trapezius muscle, supporting the potential of this device as a musculoskeletal therapeutic tool. The findings could also contribute to the further development of this device to improve its therapeutic efficacy in musculoskeletal treatment.

Keywords: Health, Prototype, Massage stick, Heat therapy, Myofascial pain

Funding: The authors would like to express their gratitude to the Faculty of Associated Medical Sciences, Chiang Mai University for providing partial funding for this research.

Citation:  Sukkasem, S., Seammativong, S., Udwai, A., and Paungmali, A. 2026. Effects of cordless heat-assisted massage device on skin temperature, tissue blood flow, and pressure pain threshold at myofascial trigger points in upper trapezius muscle. Natural and Life Sciences Communications. 25(4): e2026072.

Graphical Abstract:

INTRODUCTION

Latent trigger points are a highly prevalent musculoskeletal condition and represent a significant public health concern, affecting up to 85% of the global population (Wu et al., 2024). They are characterized by localized hyperirritable regions within taut bands of skeletal muscle or fascia and may be activated by factors such as mechanical compression, muscle overuse, prolonged stress, or muscle imbalance. Latent trigger points are associated with reduced range of motion, increased muscle stiffness, and potential sensory–motor dysfunction (Öztürk et al., 2022). The upper trapezius is among the most commonly affected muscles, with increased stiffness reported in 50–82% of cases (Xie et al., 2019). Unlike active trigger points, latent trigger points are not typically associated with acute inflammation, allowing the application of deeper manual and thermal therapeutic interventions.  Latent myofascial trigger point (MTrP) pain can be managed through various therapeutic approaches, such as acupressure, kneading massage, and heat therapy (Barbero et al., 2019; Chaithavuthi and Muangsiri, 2025). In traditional practices, locally available wooden materials have been modified into massage tools or acupressure sticks to enhance the effectiveness of manual massage and reduce the physical effort required by the therapist (Wamontree et al., 2015; Sansiriphun et al., 2023). Existing studies in this area are limited in number and largely outdated. Therefore, the present innovative study is both timely and necessary to advance the healthcare context and support its potential clinical application. Building upon this concept, the development of innovative devices that combine both mechanical pressure and heat therapy may provide more efficient, portable, and user-friendly options for trigger point management. To address this need, an innovative self-administered (or assisted) device was designed to deliver both mechanical pressure and superficial heat therapy simultaneously. The device generates superficial heat through internal coils and infrared radiation within its probe, which transfers heat to the targeted tissue via conduction. This method eliminates the need for gels or conductive media, thereby avoiding messiness or discomfort during application.  Despite the potential therapeutic benefits, the physiological effects of this newly developed cordless heat-assisted massage device on latent MTrPs have not yet been investigated. Specifically, no prior studies have examined its impact on skin temperature (ST), tissue blood flow (TBF), and pressure pain threshold (PPT) at the upper trapezius muscle. Therefore, the present study aimed to evaluate the physiological changes in ST, TBF, and PPT following treatment with the developed device compared to a sham treatment. This study forms part of the broader process of developing innovative therapeutic tools for the management of myofascial trigger point pain.

MATERIALS AND METHODS

Participants

The sample size was calculated based on pilot data, using preliminary estimates of the primary outcome (i.e., tissue blood flow) to inform feasibility and effect size assumptions, before conducting the main study.  Using the G*Power software (version 3.1.9.7), with an effect size of 0.7 for tissue blood flow, an alpha level of 0.05, and a statistical power of 80%. The required within-subject sample size was approximately 19-20 participants per condition. Therefore, this preliminary study was conducted in 20 female participants with latent myofascial trigger point (MTrP) pain. Only females were recruited for this preliminary investigation due to known sex-related differences in pain thresholds and subcutaneous blood flow (Lee et al., 1994). The inclusion criteria were as follows: age between 18 and 55 years, no history of injuries in the neck or shoulder region, presence of at least one latent MTrP on the upper trapezius muscle bilaterally. Latent MTrP was diagnosed using standardized palpation criteria, including identification of a taut band in the upper trapezius, localization of a hypersensitive trigger point nodule, and reproduction of the participant’s familiar pain with sustained pressure (Shah et al., 2015), and pressure pain threshold (PPT) at the MTrP ranging between 1.5–2.0 kg/cm². The exclusion criteria included: sensory impairments in the skin of the neck or shoulder region, dermatological conditions affecting the neck or shoulder, heat hypersensitivity, vascular disorders or contraindications/precautions for heat therapy, premenstrual phase (within one week before menstruation) or during menstruation, and presence of fever (body temperature > 38°C) (Carmeron, 2017).

Ethical considerations

The study protocol was approved by the Institutional Human Research Ethics Committee (approval number: AMSEC-67Ex-085). All participants provided written informed consent prior to data collection.

Outcome measures

Physiological outcomes were assessed over the latent MTrP of the upper trapezius muscle.  Skin temperature was measured using an infrared thermometer (Model Handheld#66, Fluke corporation, USA), tissue blood flow was assessed with a laser Doppler flowmeter (Model VMS-LDF, Moor Instruments, UK), and pressure pain threshold (PPT) was determined using a pressure algometer (Model FPK 60, Wagner Instruments, USA). Each parameter was recorded at three time points: baseline (pre-treatment), immediately post-treatment, and 5 minutes post-treatment.

Research tools

The developed cordless heat-assisted massage device was specifically designed to deliver superficial heat through the skin at a controlled temperature of 45°C. The device incorporated an internal temperature sensor to ensure consistent heat delivery. It was powered by a rechargeable battery with USB-C charging capability, equipped with a charging control circuit that displayed battery status (lasting for 30 minutes per charge). In addition, the device featured a safety mechanism to prevent electrical leakage during use.

Research procedure

The order of conditions (treatment or sham) and shoulder sides was randomized for each participant. For the treatment condition, participants received a massage at the identified latent MTrP of the upper trapezius muscle using the cordless heat-assisted massage device with the heating function activated. The probe had a diameter of approximately 1.5 inches. The applied pressure was standardized using a spring scale, set to 600 g. (i.e., comfortable sensation). Massage strokes were performed in overlapping circular motions (diameter of 2.5 inches) at a frequency of 12 cycles per minute. Each treatment session lasted 10 minutes (Figure 1). For the sham condition, the same procedure was applied to the contralateral upper trapezius muscle, but with the heating function deactivated.

Figure 1. Application of the cordless heat-assisted massage device over the latent myofascial trigger point of the upper trapezius muscle.

Data analysis

Data were first tested for normal distribution. A two-way repeated measures analysis of variance (ANOVA) was then used to determine the effects of condition (treatment vs. sham) and time (pre-treatment, immediately post-treatment, and 5 minutes post-treatment) on skin temperature, tissue blood flow, and pressure pain threshold. A significance level of P < 0.05 was considered statistically significant.  Statistical analyses were conducted in SPSS version 30.0.

RESULTS

All experimental sessions were conducted in a research laboratory maintained at a room temperature of 24.0 ± 0.5°C. General characteristics of the participants are presented in Table 1.

Table 1. Characteristics of the study participants (n = 20).

Reliability testing

Prior to the main study, intra-tester reliability of the measurement techniques was confirmed. Intra-class correlation coefficients (ICC_3,1) ranged from 0.77 (tissue blood flow), 0.82 (skin temperature) to 0.88 (pressure pain threshold), and standard errors of measurements (SEMs) for skin temperature (0.19°C), tissue blood flow (35.13 flux/min), and pressure pain threshold (0.16 kg) were less than 5%, indicating acceptable reliability.

Main outcomes 

Application of the cordless heat-assisted massage device with the heating function activated produced significant physiological changes. Compared with baseline, both skin temperature (P < 0.01) and tissue blood flow (P < 0.001) increased significantly after treatment (Tables 2-3). In addition, the treatment condition exhibited significantly greater increases in skin temperature (P < 0.01) and tissue blood flow (P < 0.05) immediately after treatment and at 5 minutes post-treatment compared with the sham condition (Tables 2-3; Figures 2-3). In contrast, no significant changes were observed in pressure pain threshold in either condition across time points (P > 0.05) (Table 4). Main Outcomes:  Application of the cordless heat-assisted massage device with the heating function activated produced significant physiological changes. Compared with baseline, both skin temperature (P < 0.01) and tissue blood flow (P < 0.001) increased significantly after treatment (Tables 2-3).  In addition, the treatment condition exhibited significantly greater increases in skin temperature (P < 0.01) and tissue blood flow (P < 0.05) immediately after treatment and at 5 minutes post-treatment compared with the sham condition (Tables 2-3; Figures 2-3). In contrast, no significant changes were observed in pressure pain threshold in either condition across time points (P > 0.05) (Table 4).

Table 2. Mean ± standard deviation (SD) of skin temperature (ST) at the upper trapezius muscle for both study conditions (treatment and sham) at pre-treatment, immediately post-treatment, and 5 minutes post-treatment.

Note: Minimal Clinically Important Difference (MCID) for ST = 0.33°C; Effect size presented as partial Eta squared a = statistically significant compared with pre-treatment (P < 0.01), b = statistically significant compared with immediately post-treatment (P < 0.01), c = statistically significant between conditions (P < 0.01).

Figure 2. Comparison of changes (mean ± SD) in skin temperature between the cordless heated massage device treatment condition and the placebo-controlled sham condition, expressed as percentage change (%Ch), immediately after treatment (0 min) and at 5 minutes post-treatment (5 min).

Table 3. Mean ± standard deviation (SD) of tissue blood flow (TBF) at the upper trapezius muscle for both study conditions (treatment and sham) at pre-treatment, immediately post-treatment, and 5 minutes post-treatment.

Note: Minimal Clinically Important Difference (MCID) for TBF = 32.13 flux/min; Effect size presented as partial Eta squared a = statistically significant compared with pre-treatment (P < 0.001), b = statistically significant compared with immediately post-treatment (P < 0.01), c = statistically significant compared with immediately post-treatment (P < 0.05), d = statistically significant between conditions (P < 0.05).

Figure 3. Comparison of changes (mean ± SD) in tissue blood flow between the cordless heated massage device treatment condition and the placebo-controlled sham condition, expressed as percentage change (%Ch), immediately after treatment (0 min) and at 5 minutes post-treatment (5 min).

Table 4. Mean ± standard deviation (SD) of pressure pain threshold (PPT) at the upper trapezius muscle for both study conditions (treatment and sham) at pre-treatment, immediately post-treatment, and 5 minutes post-treatment.

Note: Minimal Clinically Important Difference (MCID) for TBF = 0.14 kg/cm²; Effect size presented as partial Eta squared, ^NS = non-significant from pre- to post-, and between conditions.

DISCUSSION

Skin temperature

In the treatment condition, skin temperature increased significantly immediately post-treatment and at 5 minutes post-treatment compared with baseline (P < 0.01). Clinically, effective superficial heat therapy is typically defined within the therapeutic range of 40–45 °C, which promotes hyperemia (Cameron, 2017). Temperatures above 45°C may risk tissue damage or burns, whereas temperatures below 40°C may be insufficient to achieve therapeutic effects (Petrofsky et al., 2020; Freiwald et al., 2021). The observed increase in skin temperature with the cordless heat-assisted massage device is primarily attributed to conduction of heat from the device to the skin and underlying tissue. Despite the relatively cool laboratory environment (24.0 ± 0.5°C), skin temperature remained significantly elevated at 5 minutes post-treatment, indicating that the intervention produced residual heating effects for at least 5 minutes. In contrast, the sham condition (device applied without heat) produced a slight reduction in skin temperature compared with baseline, likely attributable to heat conduction from the cold stainless-steel probe in a cool laboratory environment. The greater increase in post-intervention skin temperature may be also attributable to the effects of kneading massage, which enhances local blood circulation. This finding is consistent with the study by Rodrigues et al. (2020), who investigated the physiological effects of massage on the upper and lower limbs of 32 healthy volunteers. Tissue blood flow, assessed using laser Doppler flowmetry (LDF) and reflection photoplethysmography (PPG), was found to increase significantly in the massaged limbs.

Tissue blood flow

The treatment condition produced a significant increase in tissue blood flow (130–190% above baseline). At 5 minutes post-treatment, blood flow decreased slightly but remained significantly elevated relative to baseline, demonstrating a sustained effect. These findings are consistent with previous studies (Plakornkul et al., 2016; Rodrigues et al., 2020), which report that massage increases local blood flow through vasodilation mediated by nitric oxide (NO) release. Mechanical pressure generates shear stress on endothelial cells, stimulating NO production via endothelial nitric oxide synthase (eNOS), leading to relaxation of vascular smooth muscle and increased blood flow. Additionally, mechanoreceptor stimulation in the skin and underlying tissue activates parasympathetic pathways, further promoting vasodilation (Zhao et al., 2015). The heat delivered by the device likely contributed synergistically to the observed increase in tissue perfusion.

Pressure pain threshold

No significant changes in pressure pain threshold (PPT) were observed in either condition. This may be due to suboptimal tissue heating or insufficient mechanical pressure to elicit analgesic effects. Optimal superficial heat therapy requires tissue temperatures within 40–45 °C; temperatures below this range may not produce sufficient physiological responses (Cameron, 2017; Petrofsky et al., 2020; Freiwald et al., 2021). Moreover, in this study, massage pressure was set to a comfortable, non-painful level, and participants had mild baseline discomfort of trigger point (PPT = 1.74–1.83 kg/cm²), potentially limiting detectable changes in PPT due to a ceiling effect (Kashyap et al., 2018).  A non-significant change in PPT is consistent with the findings of Boonruab et al. (2018), who compared herbal compress massage with diclofenac treatment in patients with myofascial pain syndrome of the upper trapezius. Their results demonstrated that herbal compress massage was more effective in pain reduction and significantly improved cervical range of motion (P < 0.05), whereas PPT changed only slightly and non-significantly in both the herbal compress and diclofenac groups (P > 0.05). Furthermore, Fryer and Hodgson (2005) reported that manual pressure release for latent myofascial trigger points in the trapezius requires an adequate and sustained pressure, typically perceived as “moderate but tolerable pain” (approximately 5–7/10 on the numerical rating scale), to alter pressure sensitivity. In the present study, the device was applied at a comfortable, non-painful pressure, which may partly explain the minimal changes observed in PPT. Additionally, the intervention consisted of a single treatment session, which may be insufficient to elicit measurable changes in PPT compared with repeated or longer-term interventions.

Study limitations and further study:  This study investigated only the immediate effects of the intervention in female participants aged 18–25 years and focused on the upper trapezius muscle, which may limit the generalizability of the findings to male patients, other age groups, or muscle regions. Moreover, the intervention targeted localized trigger point treatment only, whereas clinical management should also address contributing factors (e.g., poor posture and non-ergonomic work environments). Further research is warranted.

CONCLUSION

Application of a cordless heat-assisted massage device significantly increased skin temperature and tissue blood flow at latent myofascial trigger points of the upper trapezius compared with a sham condition, with effects persisting for at least 5 minutes post-intervention. No significant changes were observed in pressure pain threshold. These findings provide preliminary support for the use of this device as a therapeutic tool, informing future device development and clinical research.

ACKNOWLEDGEMENT

The authors would like to express their sincere gratitude to all participants for their contribution to this study. We also thank The Knowledge Centric and Paw Partners Co., Ltd. for developing and providing the prototype cordless heat-assisted massage device.

AUTHOR CONTRIBUTIONS

Aatit Paungmali: Conceptualization (Lead), Methodology (Lead), Formal Analysis (Lead), Validation (Lead), Resource (Lead), Writing – Original Draft (Lead), Writing – Review & Editing (Lead), Investigation (Equal), Supervision (Lead), Project administration (Lead); Sasipreeya Sukkasem: Data Curation (Equal), Formal Analysis (Equal), Writing – Original Draft (Equal), Writing – Review & Editing (Equal), Investigation (Lead); Suchanalee Seammativong: Data Curation (Equal), Formal Analysis (Equal), Writing – Original Draft (Equal), Writing – Review & Editing (Equal), Investigation (Lead); Apisara Udwai: Data Curation (Equal), Formal Analysis (Equal), Writing – Original Draft (Equal), Writing – Review & Editing (Equal), Investigation (Lead).

CONFLICT OF INTEREST

The authors declare that they have no conflicts of interest.

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