The validity of a non-invasive blood lactate sensor

Blood lactate is routinely measured in endurance athletes to determine the physiological responses to exercise. The blood lactate profile allows the determination of thresholds that can be used to inform training and is often reported as the corresponding heart rate, speed, or power output. Wearable technology development has allowed blood lactate to be estimated in real-time rather than being restricted to laboratory-based testing during a single session. Following institutional ethical approval, eight male participants provided written informed consent to take part in this study. Each participant completed a lactate threshold testing protocol, starting at an intensity of 100 W, with 25 W increments observed every three minutes. At the end of each stage, a capillary blood lactate sample was taken (Biosen C-Line, Sport). Throughout testing, it was anticipated that blood lactate could be estimated using bioimpedance spectroscopy (Zelemiq, UK sensor). There were two aspects of data analysis: firstly, to determine the predictive quality of blood lactate values from the Zelemiq sensor, and secondly, to observe the agreement of lactate thresholds derived from capillary blood lactate and the Zelemiq sensor values. Both Zelemiq and blood lactate values were standardised within participants, with results demonstrating an exponential quadratic relationship. The greatest agreement in threshold detection was observed when using the ModDmax method with a bias of -0.95 [95% confidence interval: -13.85, 11.95] W. Further work is required to determine the baseline variation between participants and test the quadratic model.