Carme Martín-Borràs ¹ Gemma González Serra ² Noèlia Carrasco-Querol ^1* Oriol Sansano-Nadal ¹ Nerea Bueno Hernández ¹ Pau Bestraten del Pino ³ Marta Pastor Cazalla ³ Rosa Caballol Angelats ⁴ Pilar Montesso Curto ⁴ Elisabet Castro Blanco ¹ Macarena Pozo ¹ José Fernández-Sáez ¹ MR Dalmau Llorca ⁴ Alessandra Queiroga Gonçalves ¹ Carina Aguilar Martín ¹

• ¹ Unitat de Suport a la Recerca Terres de l'Ebre, Fundació Institut Universitari d'Investigació en Atenció Primària Jordi Gol i Gurina (IDIAP JGol), Tortosa, Spain
• ² Hospital de Tortosa Verge de la Cinta, Tortosa, Spain
• ³ Servei de Rehabilitació d'Atenció Primària Terres de l'Ebre, Insitut Català de la Salut (ICS), Tortosa, Spain
• ⁴ University Institute for Primary Care Research (IDIAP Jordi Gol), Barcelona, Catalonia, Spain

Introduction: Fibromyalgia (FM) and chronic fatigue syndrome (CFS) are complex central sensitization syndromes that represent an important public health problem. Low cardiorespiratory fitness and muscle function with habitual intolerance to efforts are common characteristics of FM and CFS. This study aimed to examine the effect of a brief multicomponent intervention based on physical activity (PA), nutrition, and chronobiology on movement behaviors (PA, sedentary and sleep time), muscle strength, and cardiorespiratory capacity. Methods: randomized controlled trial was conducted in primary healthcare in Catalonia. A total of 143 individuals with FM or FM and CFS concomitantly (age 50.80, SD 8.109; 94.41% women) were randomly allocated to the intervention (IG, n=69) or control (CG, n=74) groups. The IG participated in a brief multicomponent (PA, nutrition, and chronobiology) group-based intervention (4 sessions, 3 hours/session) while the CG received usual primary care practice. Primary outcome measure was PA measured by the REGICOR-Short Physical Activity Questionnaire. Secondary outcomes were sedentary (International Physical Activity Questionnaire) and sleep time (Pittsburgh Sleep Quality Index), upper-and lowerbody muscle strength (handgrip and sit-to-stand test, respectively), and aerobic capacity (6-min walk test). Data were collected at baseline and 3 months post-intervention. Results: The IG showed positive differences at 3-month follow-up, with highly significant appreciably PA levels, less sedentary time, and significantly improved sleep time. Significant between-group differences were also observed at 3 months, with better health values in the IG: significant PA and sleep time (370.30±3076.095 vs. 195.92±289.11 min/week and 6.10±1.658 vs. 5.547±1.876 h/night, respectively) and less sedentary time (266.25±153.31 vs. 209.42±199.89 min/day). The IG also showed higher upper limb strength and significant lower-body strength both between and within groups, as well as significantly improved cardiorespiratory capacity. Conclusions: The Synchronize+ multicomponent program implemented at primary healthcare has shown short-term effectiveness in improving 24-hour movement behaviors and health outcomes in individuals with FM, with or without CFS. This intervention may be a first step in educating and motivating people with FM and CFS to adopt an active lifestyle, leading to improved health. Long-term follow-up will determine whether the changes are maintained over time and their impact on quality of life and healthcare costs.