Fibromyalgia syndrome (FMS) is a chronic pain condition affecting up to the 6.6% of the general population1, being the third most common musculoskeletal condition after lumbar pain and osteoarthritis2. The annual economic burden per FMS patient is estimated at $38043. FMS is characterized by a plethora of symptoms including widespread pain, physical and mental fatigue, morning stiffness, anxiety, depression, cognitive dysfunctions, sleep problems, autonomic disturbances, exacerbated pain responses (indicators of central sensitization), and reduced health-related quality of quality of life (QoL)4,5,6.
Consistent evidence identifies several sociodemographic, physical, biological, lifestyle, and psychological factors, such as depression, obesity, older age, dietary patterns, smoking, alcohol consumption, higher cortisol levels, greater risk of fall, female sex, lower income and education level, associated with frailty affecting health-related QoL and activities of daily life (ADL)7. Therefore, the fact that the age peak for suffering from FMS is 50–60 years old, the presence of altered cortisol levels, the high prevalence of other associated comorbidities (e.g., anxiety and depression), and considering that 80–90% of FMS sufferers are women8,9could explain the high impact of FMS on QoL and ADL.
In addition, muscle weakness is a risk factor for developing earlier disability onset and dependence during ADL10and a preventable contributor to the global burden of morbidity and mortality11. Previous reports have shown that muscle strength is generalized reduced up to 35% of magnitude when comparing FMS women with healthy women12. This generalized weakness may be explained by pathologic changes in muscle fibers, impaired blood circulation, disturbances in regulation of growth and energy metabolism, altered neuromuscular control mechanisms associated with pain and decreased levels of physical activity associated with fear avoidance behaviors, pain, and overweight13,14.
The Hand Grip Force is a reliable, simple, and noninvasive test assessing the strength of the hand muscles used to grasp or grip15,16. This test is considered as a valid indicator to identify frailty and risk of disability among elderly people as is associated with cardiovascular, respiratory, and cancer outcomes and also with mortality17. Evidence supports the presence of reduced hand grip force in women with FMS18,19,20,21,22,23. In addition, reduced hand grip force has been associated with worse severity19,20, higher related-disability21, lower pulmonary muscle strength22, and worse health-related quality of life23in women with FMS. On the contrary, others did not find an association between hand grip force and severity18,23.
The Time Up and Go test is a physical performance test complementary to the hand grip commonly used tool for screening falls risk and is also considered as a strong predictor of short-term mortality24,25. Most previous studies conducted in FMS included sample sizes 13but also in other pain conditions, e.g., low back pain26. Therefore, the aims of the current study were to analyze the correlation between demographic, pain-related, disease-specific, psychological, physical function measures and hand grip force and also to develop a linear regression model to analyze factors explaining the variance of hand grip force in women with FMS (Fig. 1).