# Wearable Inertial Devices in Duchenne Muscular Dystrophy: A Scoping Review
## 4 Discussion
### Technical Perspective  
In all research, the compact and easy-to-use configuration of wearable sensors has proved to be a positive and crucial advantage for physical activity monitoring during daily routine, home monitoring, and tele-rehabilitation. This solution allows possible limitations to be overcome, namely those due to clinical analysis in laboratory settings and indoor environments, and the alteration of movements caused by the consciousness of being observed. Moreover, continuous and prolonged monitoring allows the registration of a large amount of data, which increases the robustness and reliability of the final results. Instruments' small dimensions and their lack of invasiveness contribute to acceptance of wearing them for a long interval of time for both patients and caregivers. Several typologies of wearable devices were used in the current research (Table 2), both customized systems [32; 33] and commercial products [41; 42; 47; 50]. The configuration of a 3-axis accelerometer was shown to be the most widespread in the past, but in the last few years studies have proposed the use of inertial sensors, including accelerometers, gyroscopes, and magnetometers. Most of the studies used the accelerometric measurement system as actigraphy, in particular to monitor patients' physical activity levels [34; 43], to differentiate the type of activity performed (walking, sitting, lying) [33], to distinguish between sedentary and active behavior [36; 50], to represent sleep quality [41; 53], and to assess the total amount of steps during walking in ambulatory subjects [45; 46]. The integration of a 3-axis gyroscope and a 3-axis magnetometer contributes to the definition and calculation of objective outcomes suitable for measuring the human segment's orientation and for describing more complex movements, also involving the upper body part of the human [35; 39; 42].  
It is important to underline that, among the different wearable devices, the ActiMyo sensor has been recognized as a Class I medical device [48]. It is composed of a base station for charging units and data transmission, and two wearable units. ActiMyo units continuously measure acceleration, velocity, and orientation over prolonged intervals of time and with high accuracy. The device can be worn by the subject both at the wrist and ankle joints. Moreover, studies demonstrated its potential in the identification of meaningful clinical improvements. Based on European regulatory requirements, the wearable sensor ActiMyo is currently the only suitable and validated device for gathering SV95C data in clinical gait trials. Other acquired endpoints are likely to be identified and verified in both ambulatory and non-ambulatory neuromuscular diseases [48].  
Based on the performed motion, sensors have been positioned in correspondence to different human body parts (Figure 2A). In particular, results pointed out that the most suitable configurations for monitoring lower-body activities and evaluating walking steps require the positioning of sensors on the pelvis and/or ankle joints of the patient. When monitoring upper-body motions, sensors must be referred to the chest, the upper arm, and/or the lower arm. The positioning of inertial sensors on the wrist joints (dominant and/or non-dominant arm) revealed themselves as suitable for movements involving both upper- and lower-body segments.