The rise of wearable sensors to measure lactate content in human sweat during sports activities has attracted the attention of physiologists given the potential of these “analytical tools” to provide real-time information. Beyond the assessment of the sensing technology per se , which, in fact, has not rigorously been validated yet in controlled conditions, there are many open questions about the true usefulness of such wearable sensors in real scenarios. On the one hand, the evidence for the origin of sweat lactate (e.g., via the sweat gland, derivation from blood, or other alternative mechanisms), its high concentration (1–25 mM or even higher) compared to levels in the blood, and the possible correlation between different biofluids (particularly blood) is rather contradictory and generates vivid debate in the field. On the other hand, it is important to point out that accurate detection of sweat lactate is highly dependent on the procedure used to collect and/or reach the fluid, and this can likely explain the large discrepancies reported in the literature. In brief, this paper provides our vision of the current state of the field and a thoughtful evaluation of the possible reasons for present controversies, together with an analysis of the impact of wearable sweat lactate sensors in the physiological context. Finally, although there is not yet overwhelming scientific evidence to provide an unequivocal answer to whether wearable sweat lactate sensors can contribute to sports physiology, we still understand the importance to bring this challenging question up-front to create awareness and guidance in the development, validation, and implementation of wearable sensors.

This work presents a flexible cable-shaped supercapacitor based on carbon fibers (CFs) coated with graphene flakes (GFs) for wearable electronic applications. The CF bundles were adopted as base materials and the GFs were coated on the surface of CFs using a simple dipping method for the enhancement of the specific surface area and the higher conductivity of flexible electrodes. H 2 SO 4 was mixed with poly(vinyl alcohol) (PVA) to form a gel electrolyte, which can prevent leakage. Polydimethylsiloxane (PDMS) was selected as a packaging material to fabricate the proposed flexible supercapacitor due to its flexibility and good thermal and chemical stability. From the electrochemical analysis, the fabricated device exhibited 15.099-6.492 mF/cm 2 of specific capacitance and 2.097-0.902 µWh/cm 2 of energy density in the range of 50-300 mV/s of scan rate. These values were about 1.9 times larger than the supercapacitor without being coated with the GFs. In addition, the specific capacitance showed small difference of 3.4% between straight and twisted positions, which assures the mechanical stability of the flexible cable-shaped supercapacitor. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

In the last decade, sport performance assessment has significantly transformed due to the appearance of disruptive technologies. Subjective pen and paper notations have evolved into advanced wearable sensing systems that acquire performance-related data. The selection of adequate performance metric variables always causes a debate in sport physiology, and this becomes more relevant once new biochemical indicators are proposed, such as sweat lactate. Here, we analyze the correlation of real-time sweat lactate, obtained with a validated wearable biosensor, with the typical physiological parameters often recorded in sports laboratories (e. g., blood lactate, Borg scale for the rating of perceived exertion, heart rate, power output, blood glucose, and respiratory quotient). We found that the heart rate, power output, Borg scale, and blood lactate relate to sweat lactate in independent individuals during cycling activity. Hence, we demonstrate the potential to associate non-invasive, quantitative, and personalized analysis with sport practice.

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