Feedback control of oxygen uptake profiles during robotics-assisted treadmill exercise

Gait rehabilitation robots have potential for cardiovascular rehabilitation of patients with neurological deficits. A novel method was developed to guide exercise intensity by feedback control of oxygen uptake rate with a focus on tracking ramps as typically applied in maximal exercise testing. This approach is important as prior observations have noted a non-linear oxygen uptake response to increasing work rate, whereas a linear progression of exercise intensity is desirable. The proposed oxygen-uptake controller has embedded within it a human-in-the-loop feedback system for control of mechanical work rate which takes its target work rate from the automatic oxygen uptake control loop. Results of step and ramp tracking of target oxygen-uptake profiles, and disturbance rejection tests, demonstrated the technical feasibility and accuracy of the approach. Comparison with open-loop tests demonstrated clearly that the feedback system linearises the oxygen-uptake response and that linear progression of exercise intensity leads to higher peak oxygen uptake values. Further work will focus on clinical feasibility and the potential for cardiovascular rehabilitation in patients with neurological deficits.