# Wearable Inertial Devices in Duchenne Muscular Dystrophy: A Scoping Review
## 4 Discussion
### Biomechanical Perspective  
Several biomechanical variables were obtained from acceleration and angular velocities raw data. These variables were selected and investigated with a strong dependence on the human task performed. The first and most commonly proposed analysis dealt with the differentiation between sedentary behavior and physical activity, followed by recognition of the activity (walking, sitting, lying down) in a home environment. These analyses can be conducted for all DMD patients, without considering walking ability as possible inclusion/exclusion criteria. Nevertheless, significant differences were stressed in the comparison between ambulatory and non-ambulatory DMD patients [43].  
In case of ambulatory patients, both posture and walking parameters have been analyzed. Due to the crucial treatment goal of maintaining walking ability as long as possible, several studies focused on the evaluation of gait parameters, such as stride velocity, stride length, cadence, number of meters walked per hour, and average daily steps. Among them, as already stressed, European regulators considered SV95C to be an acceptable secondary endpoint in pivotal or exploratory drug therapeutic studies for regulatory purposes, when measured continuously and in a home environment by a valid and suitable wearable device [40]. This crucial result has been reached after numerous investigations on accuracy, reliability, and sensitivity of the selected parameter. It is not only an important and recognized assessment of the potential of objective biomechanical parameters as outcome measures, but also a fundamental milestone in the recognition of wearable devices as suitable instrumentation for clinical trial assessments. Despite the numerous studies and the confirmation of significant differences in walking ability between MD patients and healthy controls, the lack of investigation into spatio-temporal parameters describing the different phases and subphases of a gait cycle, such as stance duration, swing duration, single and double support, step length, and step width, must be stressed. Moreover, despite large interest in the evaluation of gait symmetry and the application in other clinical circumstances, only one study proposed the investigation of gait smoothness based on the spectral entropy of the acceleration norm monitored at the trunk [33], while another proposed a new relative coupling coefficient index (RCC) for assessing motor coordination during the walking trial [42]. Additional future investigations might be conducted to enhance the biomechanical description of gait characteristics.  
Only a few studies focused on the evaluation of objective measures in non-ambulatory DMD patients [35; 38; 39]. Indeed, it is more difficult to define and describe repetitive and cyclic movement for the investigation of upper limb dysfunctions. Acceleration and angular velocity data were combined and post-processed to define parameters of interest, such as the rotation rate, the hand elevation rate, the ratio between the vertical and the overall acceleration, the estimated mechanical power of the upper limb, the jerk, and the cumulative jerk of acceleration norm. All these parameters were preliminarily investigated and discussed, stressing their correlation with clinical and functional scales (PUL, Brooke). Nevertheless, the majority of studies proposed instrumental evaluation with IMUs during long periods of home monitoring [38; 39], while only one study [35] used instrumental monitoring in combination with the functional scale during the simulation of daily activities in a laboratory setting. Moreover, the kinematic orientation of different human body parts (trunk, upper arm, lower arm) performed during validated tasks of the functional scales were not investigated. The definition and validation of suitable biomechanical parameters that can be simultaneously combined with clinical evaluation and recognized as clinical outcome measures for DMD patients are still open challenges and under research.