## 1 Introduction  
Two out of three adults may require rehabilitation at some point during the course of a musculoskeletal disorder [1], and this figure is expected to increase [1, 2]. Spinal pain, together with knee and hip osteoarthritis (OA), ranks among the most prevalent and limiting musculoskeletal conditions [3] for which exercise is usually recommended as a first-line care approach [4, 5]. Exercise-based interventions have been shown to enhance symptoms and decrease disability in individuals with chronic musculoskeletal pain [6, 7, 8, 9]. However, exercise therapy is often omitted or sub-optimally prescribed [5, 10]; thus, the impact of exercise on patients with knee OA, low back pain, or neck pain tends to be small to moderate [7, 11, 12] and not clinically relevant [8, 11]. Indeed, more than 50%of patients may not respond positively to exercise [13] aiming to reduce pain [14; 15] or improve function [14]. Exercise therapy is not a \"one-size-fit-all\" solution, and many clinical, contextual, and psychosocial factors can modulate its effects. Previous research suggests that aspects such as age, pain intensity, treatment expectations, and employment status [16; 17] can have an impact on the effect of exercise. For example, higher levels of pain and disability at baseline have been correlated with better outcomes following exercise-based interventions [18].  
Exercise programs need to be both meaningful and achievable [19] to increase treatment adherence [20; 21] and facilitate successful rehabilitation [19]. Exercise should be tailored to the individual's characteristics, preferences, and capabilities [19; 22]. In this context, new technologies offer opportunities to enhance prescription in the form of telee-habilitation [5; 23]. Current evidence supports telerehabilitation as a cost-saving resource for the management of chronic musculoskeletal pain [24; 25]. It represents a good alternative to simplify access to clinical care [26], adapt exercise regimes, and monitor patients' progression and engagement with the intervention [7; 27; 28]. The widespread use of mobile devices [29] makes mobile apps easily accessible across healthcare [30; 31]. mHealth, defined as 'health practice supported by mobile devices' [32], is showing an increasing trend in providing self-management strategies for people with musculoskeletal pain [30; 33]. Specifically, digital interventions include motivating and enjoyable interventions through treatment gamification. These features applied gaming elements to maintain patient adherence and engagement with therapy, which can improve clinical outcomes [28; 34]. mHealth is clinically feasible and effective in implementing exercise therapy [1; 35; 36], and it has proven beneficial in enhancing recovery [35; 36; 37; 38] and saving healthcare resources [27] among different musculoskeletal disorders. The impact of mHealth on improving pain and function in those with chronic pain may vary based on the particular condition, the specific mHealth modality, and the individuals' characteristics [35; 36]. A better understanding of the factors associated with the outcome following exercise therapy in patients with chronic pain is warranted to identify potential responders [13]. Exploratory analyses suggest that psychological [39], racial, and ethnic factors [40] can influence the effect of digitally delivered exercise interventions in adults with musculoskeletal pain. This systematic review aims to gather evidence on factors associated with changes in pain and function following mHealth-based exercise therapy in individuals diagnosed with chronic musculoskeletal pain. Possible associations between changes in pain and physical function will be also explored.