Electrical impedance of the torso is associated with the pressure pain threshold on myofascial trigger points in patients with chronic neck pain: A cross-sectional study

BACKGROUND: Myofascial trigger points are dysfunctional structures present in skeletal muscles and are related to sensory, motor, and autonomic changes. Despite scientific advances in recent decades in the measurement of musculoskeletal pain, evaluation of this clinical phenomenon is supported with instruments that, although valid and reliable, have a considerable degree of subjectivity. OBJECTIVE: To correlate electrical impedance of the upper limbs and torso with pain intensity, functional capacity, catastro-phizing, pressure pain threshold, and skin temperature on myofascial trigger points in the upper trapezius muscle of patients with neck pain. METHODS: A single-blind cross-sectional study. Twenty-eight volunteers of both genders were included in the study, were aged 18-45 years, and had chronic neck pain and myofascial trigger points in the upper trapezius. The volunteers were assessed using the Numeric Rating Scale, the Neck Disability Index, the Pain-Related Self-Statement Scale, algometry, infrared thermography, and electrical bioimpedance. RESULTS: The following significant results were observed: a negative association between the pressure pain threshold on myofascial trigger point in the right upper trapezius and electrical impedance of the torso at 5 kHz (r(s) = -0.392, p = 0.032), 50 kHz (r(s) = -0.406, p = 0.026), 250 kHz (r(s) = -0.388, p = 0.034), and to the frequency 500 kHz (r(s) = -0.444, p = 0.014). CONCLUSION: Electrical impedance of the torso is associated with the pressure pain threshold of myofascial trigger points on the upper trapezius of individuals with neck pain. Thus, individuals with a lower pressure pain threshold have higher electrical impedance values of the torso and vice versa.