Preliminary Study of a Flexible Printed Multi-Sensing Platform for Electromyography and Lactate Measuring during Rehabilitation

Real-time measure of muscular fatigue during physical exercise is highly demanded in fields as rehabilitation and physiotherapy, both hospital and home-based. In addition to the well-accepted features extracted from EMG measurements, an increasing interest has been recently addressed to the investigation of biochemical fatigue markers to drive additional information on fatigue evolution. We propose here a multi-sensing non-invasive approach to measure fatigue through EMG and lactate sensing. A printed unobtrusive sensing patch was developed as first prototype by means of the emerging Aerosol Jet Printing technique, ensuring high repeatability and stability even on a flexible substrate. To study the behavior of this patch, preliminary measurements were acquired to perform an analysis of both the printed sensors. EMG electrodes, with skin-electrodes impedance magnitude and phase angle with trends comparable to commercial electrodes, showed the possibility to successfully extract mean and median frequencies from EMG and to detect their decrease after intense exercise. Preliminary results on lactate static measure showed a limit of detection of 3.1±0.3 mM with the highest linearity (R=0.9995) and sensitivity (0.39 µA/mM) in the range 0-20 mM. Furthermore, dynamic tests permitted a preliminary analysis on the ability of the sensor to measure changes in the concentration of lactate continuously. Overall, reported measures represent a promising starting point to develop a patch easily integrable in any wearable for noninvasive and totally customized fatigue measure during physical exercise.