Wearable inertial sensors have undergone great development offering an easy approach to track physical activity for both athletes and for the general public. Their immense potential to assess motion impairment in clinical practice is now fostering research on evaluation protocols, sensor configurations, and significant metrics that could be helpful to evaluate the condition of patients with a motor disease. This systematic review provides a clear picture of the current state-of-art in this research area, outlining the dominant trends, promising opportunities for future work and some guidelines to pursue them. We review Inertial Measurement Unit-based systems that have been used to assess upper limb kinematics in people with acquired neurological disease and neuromuscular disease, over the last 20 years. We evaluate the technological characteristics of the sensors and the clinical contexts in which they have been applied. Finally, we study the biomechanical metrics analyzed in the reviewed papers, focusing on those with clinical relevance to assess and evaluate the motor status of the patients.

Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA) are neuromuscular diseases that lead to progressive muscle degeneration and weakness. Recent therapeutic advances for DMD and SMA highlight the need for accurate clinical evaluation. Traditionally, motor function of the upper limbs is assessed using motor function scales. However, these scales are influenced by clinician’s interpretation and may lack accuracy. For this reason, clinicians are becoming interested in finding alternative solutions. In this context, Inertial Measurement Units (IMUs) have gained popularity, offering the possibility to quantitatively and objectively analyze motor function of patients to support clinicians’ assessments. We analyzed upper limb kinematics of two groups of children with neuromuscular diseases, seventeen DMD patients and fifteen SMA patients, while performing the corresponding clinical assessment. These two groups were further subdivided into two categories (Category A and Category B), according to disease severity (Brooke scores $$\le 2$$ ≤ 2 and Brooke scores $$>2$$ > 2 , respectively). The results were compared against a group of ten healthy children. The metrics showing the strongest correlation with the clinical score were the workspace area in the frontal and transverse plane (DMD: $$\rho$$ ρ = 0.94 and $$\rho$$ ρ = 0.90; SMA: $$\rho$$ ρ = 0.78 and $$\rho$$ ρ = 0.81) and the workspace volume (DMD: $$\rho$$ ρ = 0.92; SMA $$\rho$$ ρ = 0.81). Additionally, statistically significant differences were found not only between healthy children and those with neuromuscular disease, but also across severity levels within the patient group. These results represent a first step toward validating IMU-based systems to helping clinicians to accurately quantify the motor status of children with neuromuscular diseases. Furthermore, data collected with inertial sensors can provide clinicians with additional information not available through subjective observation.

Inertial Measurement Units (IMUs) represent a valid alternative to standard clinical assessment methods, such as clinical scales, for evaluating upper limb kinematics. A key aspect of utilizing IMUs effectively is ensuring precise sensor-to-segment calibration, which accounts for the relative orientation between the sensor and the attached body segment. This calibration is crucial to obtain accurate results. Although reliable calibration methods are available, their application in clinical and home environments remains challenging due to their complexity. This study aimed to validate a picture-based calibration method feasible for a clinical context and compare it against other standard methods. Ten healthy subjects performed daily activity tasks while upper limb kinematics was recorded using an optoelectronic motion capture system and an IMU-based system. Four calibration methods were compared using error metrics, including root mean square deviation (RMSD) and cross-correlation (XCORR). The results demonstrate that the proposed picture-based method provides highly accurate measurements for the first and second Euler rotation angles of the shoulder, with RMSD < 15 ^° and XCORR > 0.75 across most of the tasks. For the elbow joint, all calibration methods consistently yielded precise results for the first rotation (RMSD < 15 ^° and XCORR > 0.95) across the majority of tasks. The proposed sensor-to-segment calibration method improves the accuracy of upper limb motion data recorded with an IMU-based system compared to traditional methods. Moreover, the calibration approach is easy to use, making it suitable for clinical and home environments.

Background: While the importance of the upper and lower limbs in locomotion is well understood, the kinematics of the trunk during walking remains largely unexplored. Two decades ago, a casual observation was reported indicating spine lengthening in a small sample of mostly children during walking, but this observation was never replicated. Objectives: This study aims to verify the preliminary observation that spine lengthening occurs during walking and to explore changes in spine kinematics across three different age groups. Methods: A convenience sample of 45 healthy participants was divided into three groups of 15 individuals each: children (ages 5 to 13), young adults (ages 18 to 30), and older adults (ages 50 to 70). The spinal length, defined as the distance between C7 and the coccyx, and other kinematic parameters were analyzed using a motion analysis system while participants stood and walked standing and walking at their natural cadence. Results: In all groups, the length of the spine increased while walking compared to standing. This change was primarily due to a reduction in the inferior spinal angle, which is associated with lumbar lordosis, rather than a change in the superior spinal angle, which is related to thoracic kyphosis. The average change in spinal length during the walking cycle was approximately 7% in children, while it was only about 1% in adults. We also found a reduction in the range of motion for almost all the variables in adults. Conclusions: The increase in the spinal length during walking is related to a reduction in the physiological spine curve. This occurs due to muscle contractions which are needed to stabilize the locomotor system. As people age, the reduction in spinal length changes is associated with decreased spinal mobility and to a natural tendency toward anterior trunk flexion.