FDI and APL Muscle Activation During Thumb Exercises in CMC Osteoarthritis

The aim of this study is to investigate whether there are differences in muscle activation of the First Dorsal Interosseous (FDI) and the Abductor Pollicis Longus (APL) between individuals with and without trapeziometacarpal osteoarthritis (TMC OA) of the thumb. The study also seeks to identify which exercises are most effective for activating these muscles, in order to inform rehabilitation strategies for patients. The FDI has been defined as a key stabilizer of the thumb TMC joint. However, the literature reports various protocols for FDI activation and limited information on APL behavior during these exercises. OA TMC of the thumb can cause pain, decreased thumb strength, impaired hand function, and difficulty performing activities of daily living (ADLs). Appropriate rehabilitation is essential to maintain muscle function, limit joint degeneration, and improve hand performance; however, the exercises that optimally activate the FDI and APL muscles are not yet established. Participants will perform a series of standardized exercises and functional tasks designed to activate the FDI and APL muscles. Exercises include FDI strengthening with elastic bands in different hand positions (palmar and ulnar support), as well as exercises with the thumb in greater abduction. Functional tasks simulating everyday activities (e.g., turning a key, picking up a coin, writing, squeezing a tube of toothpaste, and holding a glass of water) will also be performed. Muscle activity will be recorded using surface electromyography (sEMG) during all tasks. Adults aged 40 years and older, both men and women, with TMC osteoarthritis and healthy controls without osteoarthritis will be invited to participate. Researchers will measure the activation patterns of the FDI and APL muscles during FDI activation exercises . The study aims to identify exercises that optimally activate these muscles, providing evidence to guide the rehabilitation of patients with thumb base osteoarthritis.