(a–c) The corresponding blue plots represent the real-time lactate concentration profiles for each subject, while, the red plots depict the heart rate data obtained by the electrocardiogram electrodes of the Chem–Phys patch. The black plots correspond to the heart rate data recorded by the Basis Peak heart rate monitor. Typical real-time electrocardiogram data obtained before, during and after the cycling bout for each subject is also shown. (d) Additional heart rate data from subject #1. (e) Response of the control amperometric sensor (without LOx enzyme) for subject #1.