Introduction: The assessment of metabolic responses to exercise is central to performance diagnostics in endurance sports (Westhoff et al., 2013). Lactate thresholds are commonly used to characterize this response and to define transitions between predominantly aerobic and anaerobic energy metabolism (Faude et al., 2009). Conventional lactate assessment relies on invasive blood sampling, which restricts its applicability for frequent measurements and use outside controlled laboratory settings. Salivary lactate has been proposed as a non-invasive alternative (Segura et al., 1996), with evidence suggesting it reflects systemic lactate responses during exercise (Yan et al., 2023). However, its suitability for determining lactate thresholds remains unclear.
This study investigated whether the second lactate threshold (LT2) can be estimated from salivary lactate during graded cycling using an analytical approach adapted from the modified D‑max method.
Methods: Twenty participants (10 elite cyclists and 10 recreational athletes; 50% women) completed a graded cycling test with simultaneous blood and saliva sampling throughout exercise and up to 45 minutes post‑exhaustion. The first lactate threshold (LT1) was determined using the minimal lactate equivalent method, and LT2 was calculated using the modified D‑max method for both blood and saliva. For saliva, post‑exercise peak values were assigned a corresponding power output using a virtual workload extension. Pearson correlation analysis assessed agreement between blood‑ and saliva‑derived LT2. Additionally, variability in lactate concentrations, the time delay between salivary and blood lactate accumulation, and subgroup differences were examined.
Results: Saliva‑derived power at LT2 was strongly correlated with blood‑derived power at LT2 (R2 = 0.79, p < 0.001). Both lactate measures increased with exercise intensity. However, saliva lactate concentrations were consistently and significantly lower than blood lactate (mean difference = 5.7 mmol/L). The rise in saliva lactate lagged behind blood lactate with substantial inter-individual variability (mean delay = 6.9 ± 5.4 min). No significant differences in lactate concentrations or threshold‑related power outputs were observed between elite and recreational athletes.
Conclusion: These findings indicate that LT2 estimation based on salivary lactate is feasible when accounting for delayed kinetics through an adapted modelling approach. While systematic differences in concentration and timing persist, the strong agreement in derived threshold power indicates that saliva-based measurements reflect threshold-related changes in metabolic response. This supports the potential of salivary lactate as a practical, non-invasive alternative for endurance diagnostics. In a broader applied context, such approaches may enable more accessible and repeatable monitoring and facilitate integration into routine endurance training. These developments may, in the future, support wearable or field-based sensing technologies.
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Yan P, Qin C, Yan Z, Chen C, Zhang F. Can salivary lactate be used as an anaerobic biomarker? PeerJ. 2023; 11: e15274. DOI: 10.7717/peerj.15274.