###### Abstract  
(1) Background: This study presents a new method for the motion quantitative analysis of Duchenne muscular dystrophy patients (DMD) performing functional tasks in clinical conditions. (2) Methods: An experimental study was designed to define how different levels of external mass (light and heavy) influence the performance of the upper limbs of a tested DMD and reference subject (RS) during horizontal movements (level of the waist) under natural conditions (NC) and passive manipulator conditions (PMC); the kinematic data and muscle activity of four chosen superficial muscles (EMG) were recorded. (3) Results: A piecewise linear multi-regression analysis revealed high statistically significant results (R\({}^{2}\geq 0.75\)) between the tested muscle activities and kinematic data in the tested DMD patient and RS. These results were used to define whether the neural control of the four tested muscles (processed EMG data) was correlated more with the displacement of the wrist joint or the center of mass of the tested upper limb while performing functional tests with a given external weight in a horizontal plane under NC or PMC. (4) Conclusions: The proposed approach can be used to estimate the contributions of the tested muscles to patients' motion performance and define whether this contribution is correlated with the kinematics or dynamics of the tested arm. Duchenne muscular dystrophy (DMD); EMG; kinematic data; COM Article  
A New Approach to Assess Quality of Motion in Functional Task of Upper Limb in Duchenne Muscular Dystrophy  
Woj  
have high levels of fatty and connective tissues in their muscles, clinicians can reveal further muscle damage based on EMG data [10]. It is widely known that muscle forces are related to the functional ability of the upper limb in different external conditions [11; 12; 13; 14]. According to [15], we should broaden our knowledge referring to muscle coordination in daily life and how perturbations influence the musculoskeletal system. However, most of the reported studies were conducted under laboratory conditions and mainly healthy subjects were tested for different biomechanical purposes. Studies reported about correlation between the muscle activity and motor function of the upper extremity in tested DMD patients [15; 16] and healthy patients equipped with an external device [17; 18]. Moreover, a study [19] describes the values of the maximum joint angles of the upper limbs of DMD patients during passive and active motions along with the EMG data obtained during the motions performed in the given anatomical planes and axes. On the other hand, evidence of the force of the wrist extension and thumb adduction along with the range of motion of the upper limbs of DMD patients is presented in [20]. In the literature, one can find indexes (biomechanical metrics) used to assess the upper limb pathology [21] and disease progression [16; 22], e.g., Pediatric Upper Limb Motion Index [23], Upper Limb Motion Deviation Index [24], and Upper Body Index, which assess the manipulative movements of upper limbs [19]. The reported indexes are mainly focused on the range of motion or difference between the maximum and minimum values of the chosen joint angles, the kinematics of the movement, or the duration of the tested phases. The motion of a limb is performed by controlling the kinematics of this limb or its dynamics through muscle activations. By identifying the type of control that the tested patient uses to perform the motion, the clinician can design the most suitable strategy for the rehabilitation of the patient. Additionally, it is worth noting that kinematic assessments requiring repetitive movements are limited in DMD patients due to fatigue, which is a characteristic symptom of DMD [8; 10]. That is why assessing the quality of motion in functional tasks is a key factor to diagnosing the condition of the DMD patient and planning a subsequent intervention to help them [25; 26]. In this study, the quality of motion is treated as a collection of the following features.