Persistent musculoskeletal shoulder pain, such as rotator cuff-related complaints and frozen shoulder, is common and often leads to long-term limitations and reduced quality of life. Despite available treatment options, including exercise therapy, manual techniques and infiltrations, a significant group of patients do not experience full recovery. Growing scientific evidence suggests that chronic low-grade inflammation, metabolic disorders, such as insulin resistance or obesity, autonomic dysfunction, and changes in somatosensory processing contribute to the persistence of complaints. Within this framework, physical activity is receiving more attention as a systemic intervention. High-intensity interval training (HIIT) in particular appears to have a pronounced effect on inflammatory levels, metabolic parameters, cardiovascular function, and pain modulation in various populations. HIIT also offers practical advantages due to its short duration and higher efficiency compared to traditional endurance training. Therefore, the primary aim of the current study is to investigate the feasibility of a HIIT protocol in individuals with chronic inflammatory-driven shoulder pain. This investigation includes recruitment rate, adherence, acceptance, satisfaction, motivation, safety, and practical feasibility. A secondary aim of the current study is to explore differences between individuals with shoulder pain and asymptomatic controls in terms of inflammatory markers (C-Reactive Protein), metabolic parameters (HbA1c, blood pressure, body composition), autonomic functions (self-reported symptoms, heart rate variability) and somatosensory functions (pressure pain thresholds, temporal summation and conditioned pain modulation). This is a cross-sectional feasibility study with 30 participants (15 individuals with chronic shoulder pain and 15 asymptomatic controls). The individuals with shoulder pain participate in two sessions: a maximal exercise test on a cycle ergometer (to determine VO₂max and Wmax) and a combined assessment and HIIT session. Asymptomatic controls undergo a single assessment session. The HIIT protocol consists of five one-minute intervals of cycling at 100% of the individually determined VO₂max capacity, alternating with one minute of active rest at 50% of this capacity. The total exercise time is approximately 20 minutes. The session is supervised by an experienced physiotherapist in a research setting (MOVANT, University of Antwerp). Clinical parameters that will be assessed and stored in REDCap include demographics, shoulder pain and disability (SPADI), pain intensity (VAS), quality of life (EQ-5D), inflammation (c-reactive protein), nutrition-related inflammatory index, metabolic markers (glycosylated hemoglobin, blood pressure and body composition through bioelectrical impedance), autonomic functions (self-reported autonomic symptoms and Heart Rate Variability), and somatosensory processing (pressure pain thresholds, temporal summation, and conditioned pain modulation). Results are mainly reported descriptively, with confidence intervals to estimate effect sizes. As this is a pilot study, the design is not powered for formal hypothesis testing.The study aims to investigate whether HIIT is feasible and safe in this population and to provide initial indications of the role of systemic processes in the persistence of shoulder complaints. The results may form the basis for larger randomized studies and may contribute to a paradigm shift towards systemic approaches in the treatment of musculoskeletal pain.
