Background: Myofascial trigger points (MTrPs) in the lower trapezius have been recognized as an important source of neck pain. This study aims to compare the lower trapezius muscle strength, pressure pain threshold (PPT) and muscle thickness at rest and contraction between participants and painful vs. no-painful side with active and latent MTrPs; and to examine the associations among these variables with pain intensity, duration and disability in patients with neck pain. Methods: A cross-sectional study was carried out in 64 people with neck pain with active or latent MTrPs (34 Active MTrPs group and 30 Latent MTrPs groups). Muscle strength, pressure pain threshold and muscle thickness at rest and contraction of the lower trapezius was recorded. Results: No significant differences were found in descriptive data, dominant side, or side of neck pain. However, the Active MTrPs Group had lower pain pressure thresholds (PPT) on the neck pain side compared to the Latent MTrPs Group, indicating greater sensitivity. Muscle thickness and strength showed minor differences between groups. Pain intensity correlated moderately with pain duration and strongly with neck pain disability. Conclusions: The results of the present study showed differences in PPT on the lower trapezius muscle in active and latent MTrP in neck side pain compared to non-neck side pain. In addition, lower trapezius strength reported differences between the neck side pain compared to non-neck side pain in both active and latent MTrP. Lower trapezius muscle strength showed significant moderate association with muscle thickness at contraction.

Background: Chronic neck pain (CNP) is considered a widespread musculoskeletal condition which affects the quality of life and is associated with scapular stabilizer dysfunction patterns. This study aimed to compare the morphological, functional, and strength-related characteristics of the lower trapezius muscle (such as muscle thickness at rest and during contraction, contraction-to-relaxation ratios, contraction and relaxation velocities, and force production) between individuals with CNP and asymptomatic controls. Methods: This cross-sectional study comprises 144 participants (78 with CNP and 76 controls) aged 18–30 years. Ultrasound imaging was used to assess muscle thickness, contraction and relaxation velocities, and contraction ratios. Muscle strength, including peak force and rate of force development, was evaluated using dynamometry. Participants with CNP were categorized by neck disability index (NDI) scores into mild, moderate, and severe groups. Results: Participants with CNP showed reduced contraction velocity (0.60 ± 0.24 cm/s vs. 0.81 ± 0.44 cm/s; p < 0.001; d = 0.61), lower relaxation velocity (0.48 ± 0.28 cm/s vs. 0.58 ± 0.32 cm/s; p = 0.038; d = 0.34), and decreased peak force (4.83 ± 3.27 kg vs. 6.00 ± 3.87 kg; p = 0.043; d = 0.33) compared to controls. Muscle thickness and contraction ratio differences were non-significant. Among CNP subgroups, the contraction ratio was lower in the severe disability group compared to the mild group (0.25 ± 0.19 vs. 0.53 ± 0.33; p = 0.015). Conclusions: The present study showed functional impairments of the lower trapezius muscle in individuals with CNP, particularly reduced contraction and relaxation velocities and lower peak force, with more pronounced deficits in those with severe disability. While no significant differences in muscle thickness were found, these findings suggest that functional alterations may precede structural changes.