Musculoskeletal pain represents a significant burden on individuals and the healthcare system in Spain, where 20% of adults experience pain, and 7% suffer from it daily. Myofascial pain syndrome (MPS), one of the most frequent causes of musculoskeletal pain, affects over 85% of the general population at some point. MPS is characterized by local or referred pain and the presence of myofascial trigger points (MTrPs). Despite advancements in diagnostic technologies, the evaluation of MTrPs still largely relies on manual palpation due to the absence of conclusive findings for their objective identification.

Ultrasound presents a promising alternative as a widely available, cost-effective, and non-invasive diagnostic tool for MTrPs. While prior studies on ultrasound for MTrP detection have shown variable sensitivity and specificity (ranging from 33% to 100%), no consensus has been reached on a standardized ultrasound methodology for reliable clinical use. The ability to accurately identify MTrPs through ultrasound could shift the current paradigm, facilitating earlier diagnosis and preventing the chronicity of musculoskeletal pain, thus improving patient care and reducing healthcare costs.

This study aims to evaluate ultrasound as a potential gold standard for MTrP diagnosis and characterization. By exploring optimal ultrasound modes (B-mode, Doppler), we aim to standardize a highly reliable inter-examiner diagnostic protocol that can be easily applied in clinical practice using accessible technology, such as portable wireless ultrasound devices. Specific objectives include: 1) developing ultrasound exploration protocols for MTrP detection; 2) evaluating vibration parameters for enhanced MTrP visualization; 3) characterizing MTrPs through ultrasound by analyzing size, shape, location, and echotextural features; and 4) validating proposed protocols by correlating them with manual palpation and clinical measures.

This research will contribute significantly to understanding MTrPs, providing innovative diagnostic tools and protocols that will improve the precision and effectiveness of musculoskeletal pain assessment. The findings may also have important clinical implications for MTrP-related conditions, enhancing patient care and quality of life.

This exploratory study aims primarily to characterize myofascial trigger points (MTrPs) and identify the optimal ultrasound protocol for their real-time visualization. Participants will be subjected to vibratory stimuli applied to the MTrP location.

As a secondary objective, the study will explore variations in ultrasound imaging of muscles without MTrPs, comparing measurements taken within the same muscle between different subjects. The goal is to establish a reference point for defining the normal range of various muscle echotexture values in ultrasound images of healthy individuals. This analysis will include metrics such as mean echogenicity, coefficient of variation of echogenicity, co-occurrence, and run-length matrices, among others.

To achieve this, the study will recruit subjects without musculoskeletal disorders (with or without latent MTrPs) and those with myofascial/musculoskeletal pain (with at least one active MTrP). Ultrasound images of the gastrocnemius medialis muscle, which has been selected because of the prevalence of MTrPs and its accessibility for palpation and ultrasound, will be analyzed.

To identify MTrPs in the selected muscle, both in participants with and without pain, at least two of the following diagnostic criteria must be met: 1) a palpable taut band within the muscle; 2) the presence of a hypersensitive spot within the taut band; and 3) referred pain when the MTrP is compressed. Although we are aware of the risk of false negatives, for participants with pain, to differentiate an active MTrP from a latent one, an active MTrP must reproduce the patient's symptoms, as both active and latent MTrPs commonly exhibit a taut band and hypersensitive spot.

The analysis of the data extracted from this study aims to discern any distinguishing features that could contribute to developing a model capable of accurately identifying MTrPs. This will involve using machine learning techniques or statistical modeling.

Additionally, the study will incorporate an analysis of the diagnostic reliability and validation of MTrP exploration protocol in superficial muscles, leveraging the recruited sample. This analysis aims to validate the MTrP exploration protocol by evaluating diagnostic reliability between ultrasound and manual palpation. Manual palpation is currently the most widely accepted criterion for MTrP diagnosis. An expert physiotherapist specialized in myofascial pain will use manual palpation to diagnose MTrPs in gastrocnemius medialis muscle. Using a dermographic pen, the exact area of the MTrP, as well as a control area outside the MTrP and tight band within the same muscle, will be marked. If no MTrP is detected, a random area within the muscle of interest will be marked instead. In both cases, a cross will be drawn to ensure precision in ultrasound probe placement for both longitudinal and transverse sections. This dual evaluation approach, combining manual palpation and ultrasound, aims to provide a comprehensive and reliable assessment of MTrPs in superficial muscles. The results will further clarify the effectiveness and accuracy of the MTrP exploration protocol, offering essential insights for clinicians and researchers involved in myofascial pain diagnosis and treatment.

Inclusion Criteria:

• For participants with myofascial/musculoskeletal pain, there must be at least one active myofascial trigger point (MTrP) in the gastrocnemius medialis muscle.
• Participants without pain may or may not have latent MTrPs in the gastrocnemius medialis muscle.

Exclusion Criteria:

• Any systemic medical condition, progressive neurological disease, active rheumatic disease, severe cardiac condition, malignant neoplasm, infection or acute vascular problems, fibromyalgia, myopathy, radiculopathy, myelopathy or other neuromuscular diseases.
• History of severe trauma or surgery in the last 6 months.
• Use of pacemakers or electronic implants.
• Pregnancy status.
• Obvious cognitive impairment and difficulties in communication, comprehension or cooperation.
• Physiotherapeutic treatment of a MTrP of the gastrocnemius medialis muscle with an Invasive Physiotherapy procedure (dry needling or percutaneous electrolysis) in the last month.
• Delayed onset muscle pain ("stiffness") after very intense exertion.
• Current use of any therapy (especially pharmacological) and/or any other substance that may affect the autonomic nervous system.
• Commonly accepted contraindications for Invasive Physiotherapy procedures (unbearable fear of needles, epilepsy or convulsions, etc.).

The population from which the study groups or cohorts will be selected consists of individuals recruited through a variety of outreach channels coordinated by the research team. Recruitment efforts will include the dissemination of informational leaflets via multiple communication platforms, such as the official Instagram account of the iHealthy research group (@ihealthyeu) and the newsletter of the University of Zaragoza. Additionally, potential participants will be invited through direct communication with clients of the Valdespartera Physiotherapy Clinic (Zaragoza, Spain). The recruitment process will also involve collaboration with healthcare professionals, including physiotherapists and physicians, from several key institutions, such as the Lozano Blesa University Clinical Hospital, Miguel Servet Hospital, and the Seminario Health Center (Zaragoza, Spain). These professionals will be encouraged to inform their patients about the study and invite them to participate.

Data will be shared on a reasonable request contacting the main author once data has been published.

Anyway, Individual participant data (IPD) will be shared with other researchers in accordance with data sharing protocols and participant consent, ensuring confidentiality and ethical considerations are maintained.

Once research has been published