Self-paced heart rate control during treadmill exercise for persons with gait impairment: a case study

Introduction: A self-paced (SP) heart rate (HR) control system proposed in a
previous study was found to be feasible for healthy participants. The aims of this
work were to investigate whether the SP HR control system is feasible to achieve
accurate HR control in a participant with gait impairments, and to assess its
interaction with an existing motor-driven body weight support (BWS) system.

Methods: One participant with cerebral palsy was recruited in this case study.
Three preliminary tests were completed to determine the appropriate mean value
and amplitude of the target heart rate curve, and to identify a customised heart
rate response model. Two series of formal self-paced heart rate control tests
were then conducted to investigate the influence of different heart rate
compensators and the presence of the BWS system.

Results: The customised heart rate controller achieved improved accuracy in
heart rate control and reduced oscillation in the treadmill target speed: the rootmean-
square heart rate tracking error (RMSE) was 2.38 beats per minute (bpm) vs.
3.91 bpm (customised controller vs. nominal controller), and the average power
of changes in the treadmill target speed was 0.4 × 10^−4 m2/s2 vs. 8.4 × 10^−4 m2/s2.
The BWS system resulted in improved HR tracking accuracy: RMSE on heart rate
tracking was 3.02 bpm vs. 3.50 bpm (with BWS vs. without BWS). The BWS system
had no influence on the automatic position control accuracy: RMSE on distance
tracking was 0.0159 m vs. 0.0164 m.

Conclusion: After customising the heart rate compensator, the self-paced heart
rate control system is feasible to achieve accurate heart rate control in an
individual with gait impairments, and it can correctly interact with the
BWS system.