Can we assess exercise metabolism from skin? Metabolomic profiles in skin dialysate collected during exercise

Monitoring exercise intensity is essential for optimizing the health benefits of physical activity. Indirect calorimetry is the gold-standard method for assessing metabolic stress during exercise, though, its reliance on extensive equipment for sampling and analyzing exhaled gases restricts its widespread application. Skin interstitial fluid may represent an ideal biofluid for the continuous monitoring of whole-body metabolism and exercise intensity. However, specific metabolites in skin interstitial fluid that are more closely associated with metabolic variables measured by indirect calorimetry remain unknown. We examined which metabolites in skin interstitial fluid most closely reflect metabolic responses assessed by indirect calorimetry during a continuous graded exercise protocol. Twelve young participants (5 females) exercised at low, moderate, and high-intensity phases (25%, 50%, and 75% VO₂peak), each lasting 20 min. Skin dialysate, which reflects the composition of skin interstitial fluid, were collected via intradermal microdialysis during each exercise, and metabolites in the dialysate were measured and analyzed. Medium- and long-chain acylcarnitines in skin dialysate increased during moderate-intensity exercise in line with elevations in whole-body fat oxidation. During high-intensity phase, lactic acid in skin dialysate was elevated along with increases in whole-body carbohydrate oxidation. Many metabolites including those mentioned above in skin dialysate were correlated with whole-body metabolic responses. Our preliminary data suggest that metabolite concentrations in skin interstitial fluid may be associated with variables measured by indirect calorimetry. These findings may inform the future development of wearable devices that could potentially be used for continuous and noninvasive monitoring of exercise intensity.