Abstract
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.
Highlights
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
It is worth noting that a large proportion of the research efforts dedicated to the development of wearable chemical sensors has mainly been focused on sweat monitoring, with extraordinary contributions from eminent groups worldwide.[1−8] This is, perhaps not surprising as sweat collection is accessed through noninvasive procedures, and it presents a large variety of analytes from which to obtain physiological information
We have considered opinions from scientists actively working in the domains of wearable sensors as well as sports physiologists
Summary
To provide accurate sweat analysis measurements, the research community should strive for the right analytical assessment and validation of the detection technique and for the appropriate selection of the sample collection method. Based on the established conclusions and our own experience in the field, the following key features should be considered to achieve a reliable wearable sensor for continuous lactate detection in sweat: 1) the sampling method must encompass the subject’s perspiration and avoid any sweat evaporation and contamination risk once fixed on the skin; 2) the device is fixed to the skin to provide secretion pressure that pushes the sweat through the microfluidic channel without any contact with the environment and without any blocking of the sweat glands that may alter perspiration; 3) the device is biocompatible and safe from a cytotoxicity point of view;82 4) the sensing range must cover the sweat concentrations expected during sports practice Sweat droplets can be used to measure sweat lactate with a handheld device using potentiometric measurements.[102]
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