Persistent Cervicothoracic Muscle Mechanical Stiffness as a Potential Time-Dependent Mechanism Linking Postural Loading to Chronic Neck and Upper Thoracic Pain: A Narrative Review.

Chronic neck and upper thoracic pain are common and frequently classified as non-specific when no single structural lesion explains the presentation. Although forward-head posture, prolonged device use, sedentary behaviour, and occupational loading are often considered contributors, the association between static posture and chronic neck pain is inconsistent. This narrative review examines persistent cervicothoracic muscle mechanical stiffness as a potential time-dependent mechanism linking cumulative postural loading to chronic symptoms. The central construct is persistent or repeatedly elevated mechanical stiffness, particularly passive stiffness assessed under standardised resting conditions; active stiffness related to ongoing activation or guarding is considered distinct but potentially relevant. PubMed, Scopus, and Web of Science were searched for English-language articles published from January 1990 to June 2026 addressing cervicothoracic posture, loading, fatigue, muscle mechanical properties, and chronic neck or upper thoracic pain. Findings were synthesised narratively without meta-analysis. Static posture alone does not consistently predict chronic neck pain. Sustained or repeated cervicothoracic loading may nevertheless increase muscular demand and contribute to fatigue, altered recruitment, impaired relaxation, reduced movement variability, and mechanical stiffness when exposure exceeds tissue tolerance and recovery capacity. Persistent mechanical stiffness has been proposed as a possible contributor to pain through mechanical sensitivity, altered perfusion relative to demand, metabolic stress, nociceptive sensitisation, and pain-related guarding. However, direct cervicothoracic evidence in patients with chronic neck pain remains limited; much of the biological rationale is extrapolated from studies of general muscle pain, myofascial pain, trapezius myalgia, and experimental models. In the absence of an identified neurological or vascular cause, alterations in neural-interface mechanics have been hypothesised to contribute to nerve-like symptoms; however, any relationship with surrounding muscle mechanical stiffness remains theoretical and has not been directly established. This review proposes a testable conceptual model in which cumulative postural loading, recovery capacity, neuromuscular adaptation, cervicothoracic muscle mechanical stiffness, and pain-related mechanisms interact over time. Objective assessment may help determine whether cervicothoracic muscle mechanical stiffness precedes pain, contributes to the proposed pathway, or identifies a clinically relevant subgroup. Direct longitudinal evidence validating this proposed pathway remains limited.