Fig. 1

Data preprocessing and model validation: exemplary data for participant P04 (the raw data for this test are shown in section ‘Method’). Upper plot: HR measurement from validation data set after detrending (solid black line), simulated HR response of first-order model (\(P_{1 \mathrm{sim}}\), blue dashed line), and simulated HR response of second-order model (\(P_{2 \mathrm{sim}}\), green dashed line). Lower plot: treadmill speed from validation data set after mean removal