The chemical digitalization
of sweat using wearable sensing
interfaces
is an attractive alternative to traditional blood-based protocols
in sports. Although sweat lactate has been claimed to be a relevant
biomarker in sports, an analytically validated wearable system to
prove that has not yet been developed. We present a fully integrated
sweat lactate sensing system applicable to in situ perspiration analysis.
The device can be conveniently worn in the skin to monitor real-time
sweat lactate during sports, such as cycling and kayaking. The novelty
of the system is threefold: advanced microfluidics design for sweat
collection and analysis, an analytically validated lactate biosensor
based on a rational design of an outer diffusion-limiting membrane,
and an integrated circuit for signal processing with a custom smartphone
application. The sensor covering the range expected for lactate in
sweat (1–20 mM), with appropriate sensitivity (−12.5
± 0.53 nA mM–1), shows an acceptable response
time (<90 s), and the influence of changes in pH, temperature,
and flow rate are neglectable. Also, the sensor is analytically suitable
with regard to reversibility, resilience, and reproducibility. The
sensing device is validated through a relatively high number of on-body
tests performed with elite athletes cycling and kayaking in controlled
environments. Correlation outcomes between sweat lactate and other
physiological indicators typically accessible in sports laboratories
(blood lactate, perceived exhaustion, heart rate, blood glucose, respiratory
quotient) are also presented and discussed in relation to the sport
performance monitoring capability of continuous sweat lactate.