In the medical field, the clinicians seek instruments to quantitatively assess the patient’s movement to evaluate the progression of the disease. In the motion analysis field, there are different tools to quantify the movement: goniometer, the optoelectronic motion capture and wearable sensor. All of them have positive and negative aspects but latterly the wearable sensors are gaining popularity thanks to some of their main characteristics like small dimension, light weight and reduced price. In particular, the IMUs have gained popularity because they allow for a quantitative and objective analysis outside the laboratory. In this context, the ArmTracker will represent a useful device to objectively assess and continuously monitor the motor function of the upper limb in children with DMD and SMA.