A battery-free wearable sweat lactate sensing patch for assessing muscle fatigue and recovery.

Long-term sports and rehabilitation training require effective monitoring of muscle fatigue and recovery. Blood lactate fails to accurately reflect muscle fatigue level over extended period. Sweat lactate is a promising alternative, but its potential for assessing multi-day muscle fatigue remains unexplored. Here, we present a method for assessing multi-day muscle fatigue and recovery utilizing a high-performance, battery-free, and practical sweat lactate sensing patch. The wearable patch integrates replaceable lactate sensors and electronics that can be powered and transmits data wirelessly via near-field communication. A high-performance lactate sensor based on a novel three-dimensional microstructured electrode with a Pt/CNT-Pt composite was investigated. The synergistic effect between the electrode material and structure imparts an ultra-high sensitivity of 9.76 μA mM cm within a sufficient linear range of 0.1-30 mM. The electrode features a through-hole array to ensure sufficient oxygen supply for enzyme catalysis during skin attachment, ensuring reliable signal output. The sweat lactate profiles under different conditions were studied. Multi-day exercise experiments demonstrate a trend in initial sweat lactate levels, which is absent in initial blood lactate levels. Monitoring sweat lactate during rehabilitation training can also guide training programs. The feasibility of assessing muscle fatigue during multi-day exercise through sweat lactate levels was demonstrated. This work presented a practical method to determine lactate response and muscle fatigue level during exercise towards generating personalized training plans.