Saliva, Sweat, and Exhaled Breath as Alternative Specimens for Exercise Chemistry: Analytical Advantages, Limitations, and Comparative Progress

This critical narrative review evaluates saliva, sweat, and exhaled breath as noninvasive interface matrices for exercise chemistry rather than as general substitutes for blood or urine. It synthesizes peer-reviewed evidence on exercise-related sampling biology, analytical platforms, quantitative performance, validation limits, and translational readiness; because protocols and platforms remain heterogeneous, the evidence is interpreted qualitatively rather than pooled meta-analytically. Saliva is strongest for repeated neuroendocrine, autonomic, immune, oxidative, and short-latency metabolite measurements, but its interpretation depends on flow rate, timing, oral contamination, and normalization. Sweat is most mature for sweat rate and sodium/chloride loss monitoring and is uniquely compatible with wearable platforms, whereas sweat lactate, glucose, cortisol, and cytokines require stronger physiological validation before they can be treated as systemic markers. Exhaled breath offers second-scale access to volatile metabolism, substrate use, and airway responses, but breathomics remains instrumentally demanding and vulnerable to ventilation, diet, humidity, and ambient-air confounding. The review concludes that useful applications should match each analyte and platform to a defined exercise question, a matrix-specific validation model, and a practical decision context.