Predictions of Heart Rate and Oxygen Uptake During Exercise from Kinetics by Randomized Work Rate Changes

PURPOSE: Heart rate (HR) and respiratory oxygen uptake (V’O2) kinetics can be determined by pseudo-random binary sequences (PRBS) work rate (WR) changes. The aim of this study was to predict steady states and incremental WR responses by means of PRBS WR changes. METHODS: 13 subjects performed a complex exercise protocol which comprises a section with 5 min constant WR at 30 W and 80 W, 10 min PRBS WR changes between 30 W and 80 W and an incremental WR increase (INC, 25 W per min). From the PRBS part HR and V’O2 dynamic characteristics as impulse response, slope and offset were determined via time-series analysis. By mathematical convolution, a prediction for HR and V’O2 were calculated for the complete exercise protocol. The predictions for steady states at 30 W and 80 W and the individual correlations for the PRBS interval and the incremental part from 80 W to 175 W were calculated. Residuals between measured and predicted data were determined. RESULTS: The impulse responses confirm faster kinetics responses for HR than for V’O2 to WR changes. An average correlation coefficient between measurement and prediction was 0.64 ± 0.12 (HR) and 0.62 ± 0.09 (V’O2) for the PRBS and 0.91 ± 0.09 and 0.82 ± 0.07 for INC, respectively. Measured and predicted steady states for HR at 30 W (91 ± 11 bpm versus 95 ± 13 bpm; +4% difference) and at 80 W (120 ± 16 bpm; 115 ± 15 bpm; -4%) differed significantly. Similar but not significant differences were found for V’O2 (30 W: 0.71 ± 0.07 L min-1, 0.73 ± 0.07 L min-1; 4% / 80 W: 1.18 ± 0.08 L min-1, 1.17 ± 0.09 L min-1; 1%). Residuals showed relatively constant deviations for HR but increasing differences (= measured - prediction) with increasing V’O2. CONCLUSION: It is possible to predict steady states from PRBS data within a range of ±4%. The predictability for HR was better than for V’O2 which indicates deviations from WR-V’O2 dynamic linearity. Moreover, the resulting impulse responses imply deviations from simple first- or second order responses. This study showed that PRBS testing allows a characterization of HR and V’O2 kinetics and a limited prediction beyond the PRBS range.