Exercise intensity-dependent lactate elevation in skin interstitial fluid and its long-lasting effect

Abstract

The blood lactate threshold (LT) is a crucial marker of metabolic shifts and stress transitions during exercise, influencing optimal intensity determination and chronic exercise impact evaluation across diverse individuals. Although recent studies have explored methods for estimating blood lactate levels without blood sampling, accurate solutions for LT estimation remain undeveloped. Here, we tested the analytical capability of an ultra-minimally invasive technique for LT measurement that harnesses skin interstitial lactate dynamics using a single microneedle perfusion system. The rats were acclimated to exercise and underwent external jugular vein cannulation. Following comprehensive recovery, a 1 mm single microneedle was implanted into the back skin. This allowed for the simultaneous measurement of lactate concentrations in the blood and skin interstitial fluid during incremental treadmill exercise. Skin lactate progressively increased in tandem with blood lactate during incremental exercise, albeit with lingering post-exercise clearance that did not correlate with blood lactate. Remarkably, LT extrapolated from skin lactate showed significant alignment with blood LT. Our findings reveal the potential of skin interstitial dynamics to accurately assess LT during exercise using a single microneedle, integrating the discoveries of exercise physiology into real-world athletic and/or healthy practices.Graphical abstractRepresentative graphical image of exercise rats with inserted an ultra-minimally invasive single microneedle (A). Representative graph of LT assessed by the blood (B) and skin fluid lactate (C) dynamics. The findings suggest that LT determination using the perfusate collected by the single microneedle perfusion system can be an effective alternative to current methods for measuring blood lactate, which may be a breakthrough in the development of sports science.