# Wearable Inertial Devices in Duchenne Muscular Dystrophy: A Scoping Review
## 1 Introduction  
Duchenne muscular dystrophy (DMD) is a progressive, critical, muscle-degenerative pathology caused by mutations in the encoding dystrophin DMD gene, which inhibit production of the muscle dystrophin isoform [1]. DMD has an incidence of 1 in 5000 boys, with clinical symptoms appearing in early childhood (between 3 and 5 years of age). Even though the majority of female DMD patients are asymptomatic, up to 20% of them show moderate muscle weakness [2]. In DMD, the most common symptoms are delayed motor development, muscle weakness, gait alterations, and recurrent risk of falls. Untreated patients may become wheelchair dependent before age 10-12 and need assisted ventilation by age 20. Associated complications requiring monitoring and management include lung disease, cardiomyopathy, scoliosis, corticosteroid side effects, and educational and psychosocial issues. Patients with DMD die between the third and fourth decades of life from cardiac and/or respiratory failure. Due to its complexity and strong impact on patient wellbeing, a coordinated and multidisciplinary clinical approach is essential for an early diagnosis of DMD and for the optimal management of the primary manifestations and secondary complications [3]. The current availability of more sensitive diagnostic techniques and the early adoption of therapeutic interventions [4, 5] have the potential to improve patients' length and quality of life [6]. Several clinical scales and scores are currently used to assess and monitor the functional changes in neuromuscular disorders. In children with DMD, one of the most important therapeutic goals is to maintain independent ambulation for as long as possible, postponing spinal deformities and muscle contractures. Gait pattern and potential gait impairments are generally assessed by the 6-minute walk test (6 MWT) [7; 8], also used to assess treatment effect in clinical trials [9], or by the North Star Ambulatory Assessment (NSAA) scale, which includes 17 items and was developed specifically for ambulatory DMD patients [8; 10; 11]. The Brooke Upper Extremity Functional scale [12] and the Performance of Upper Limb (PUL) scale [13; 14] were designed specifically to measure upper-body motor performance. Tasks are targeted at weaker ambulatory patients as well as non-ambulatory patients when upper limb weakness becomes more evident. While functional motor scales are currently the most widely used assessment methods, they have some limitations, including the learning effect, limited repeatability, and lack of sensitivity to highlight relevant changes in slowly progressive diseases. During the last few decades, several innovative technologies have been proposed and adopted for the biomechanical assessment and monitoring of human movement disorders in different clinical fields [15; 16; 17]. Among these technologies, wearable inertial devices have gained prominence in recent years [18; 19; 20]. Inertial Measurement Units (IMUs) are portable, easy to use, low-cost systems that allow continuous monitoring of human movements during outdoor and daily activities. Wearable sensors are composed of a single accelerometer, a single gyroscope, and a single magnetometer, or a combination of them for three-axis measurement, and can measure several kinematic parameters, such as acceleration, angular velocity, and magnetic field. Each system can measure data in a specific direction (one-axis) or along three different directions (three-axis). Based on human motion, the units can be positioned on several human body parts, with sensor placement able to affect data measurement [21]. The interpretation of the data obtained from the three-dimensional movement analysis allows the quantification of the functional alterations related to the disease, guiding decisions such as surgical interventions and therapeutic indications. Moreover, IMUs have the potential to be widely used in tele-rehabilitation and tele-monitoring [22].