A unified heart rate control approach for cycle ergometer and treadmill exercise

Objective: To develop a unified heart rate (HR) control approach for cycle ergometer (CE) and treadmill(TM) exercise, and to empirically compare the common controller’s performance between the CE andTM.

Methods: The control method used frequency-domain shaping of the input-sensitivity function to addressrejection of disturbances arising from broad-spectrum heart rate variability (HRV). A single controllerwas calculated using an approximate, nominal linear plant model and an input-sensitivity bandwidthspecification. Fifty HR control tests were executed using the single controller: 25 healthy male participantseach did one test on the CE and one on the TM.

Results: There was no significant difference in mean root-mean-square HR tracking error: 3.10 bpm ±0.68 bpm and 2.85 bpm ± 0.75 bpm (mean ± standard deviation, bpm = beats/min); CE vs. TM; p = 0.13.But mean normalised average control signal power was significantly different: 1.59 bpm2± 0.27 bpm2vs. 1.36 bpm2± 0.28 bpm2; CE vs. TM; p = 3.5 × 10−4.

Conclusion and significance: The lower values for RMS tracking error and control signal power for the TMpoint to decreasing HRV intensity with increasing HR, because, in order to match perceived exertion forthe two modalities, mean HR for the TM was set 20 bpm higher than for the CE. These HR-intensity-dependent differences in HRV are consistent with previous observations in the literature. The unified HRcontrol approach for CE and TM exercise gave accurate, stable and robust performance in all tests, thuslending support to the concept that HRV disturbance rejection is the main issue in HR control design.