Wearable Sensors for Non-Invasive Sport Monitoring: An Overview of the STEX Project

In this work, we present the research carried out within the STEX (“Smart TEXtiles for monitoring muscle activity”) project, aimed at the development of wearable non-invasive sensors for real-time monitoring of muscle activity. The project's activities performed involved the design, fabrication, characterization and validation of two different sensors: (i) piezoresistive textile-based strain sensors for the detection of the breathing rate (BR) and (ii) flexible electrolyte-gated carbon nanotube field-effect transistor (EG-CNTFET)-based sensors for $\text{NH}_{4}^{+}$ detection in sweat. The piezoresistive textile-based strain sensors proved able to follow the chest movements during quiet breathing with a sensitivity of $\mathbf{22} \pm \mathbf{2}\%$ , while a preliminary pilot study confirmed the possibility of using them to estimate the breath-by-breath BR during cycling activity. The EG-CNTFET-based $\text{NH}_{4}^{+}$ sensors showed a linear detection range for ammonium from 0.01 to 10 mM in artificial sweat, which covers the entire range of physiological concentrations of interest, with average sensitivities of $\mathbf{0.346}\ \mu \mathbf{A}/\mathbf{decade}$ and 96.94% coefficient of determination.