Technical feasibility of constant-load and high-intensity interval training for cardiopulmonary conditioning using a re-engineered dynamic leg press

Background: Leg-press devices are one of the most widely used training tools for musculoskeletal strengthening of the lower-limbs, and have demonstrated important cardiopulmonary benefits for healthy and patient populations. Further engineering development was done on a dynamic leg-press for work-rate estimation by integrating force and motion sensors, power calculation and a visual feedback system for volitional work-rate control. This study aimed to assess the feasibility of the enhanced dynamic leg press for cardiopulmonary exercise training in constant-load training and high-intensity interval training. Five healthy participants aged 31.0 ± 3.9 years (mean ± standard deviation) performed two cardiopulmonary training sessions: constant-load training and high-intensity interval training. Participants carried out the training sessions at a work rate that corresponds to their first ventilatory threshold for constant-load training, and their second ventilatory threshold for high-intensity interval training. Results: All participants tolerated both training protocols, and could complete the training sessions with no complications. Substantial cardiopulmonary responses were observed. The difference between mean oxygen uptake and target oxygen uptake was 0.07 ± 0.34 L/min (103 ±17%) during constant-load training, and 0.35 ± 0.66 L/min (113 ±27%) during high-intensity interval training. The difference between mean heart rate and target heart rate was −7 ± 19 bpm (94 ±15%) during constant-load training, and 4.2 ± 16 bpm (103 ±12%) during high-intensity interval training. Conclusions: The enhanced dynamic leg press was found to be feasible for cardiopulmonary exercise training, and for exercise prescription for different training programmes based on the ventilatory thresholds

Control design for a lower-limb paediatric therapy device using linear motor technology

Background Rehabilitation robots support delivery of intensive neuromuscular therapy and help patients to improve motor recovery. This paper describes the development and evaluation of control strategies for a novel lower-limb paediatric rehabilitation robot, based on linear-motor actuator technology and the leg-press exercise modality. Methods A functional model was designed and constructed and an overall control strategy was developed to facilitate volitional control of pedal position based on the cognitive task presented to the patient, together with automatic control of pedal forces using force feedback and impedance compensation. Results Each independent drive for the left and right legs can produce force up to 288 N at the user's foot. During dynamic testing, the user maintained a variable target position with root-mean-square tracking error (RMSE) of 3.8 ° with pure force control and 2.8 ° with combined force/impedance control, on a range of periodic motion of 20–80 °. With impedance compensation, accuracy of force tracking was also slightly better (RMSE of 9.3 vs. 9.8 N, force/impedance vs. force control only). Conclusions The control strategy facilitated accurate volitional control of pedal position and, simultaneously, accurate and robust control of pedal forces. Impedance compensation showed performance benefits. Control accuracy and force magnitude are deemed appropriate for rehabilitation of children with neurological impairments, but, due to current levels required, linear motor technology may not be suitable for applications where higher force is needed. Further work is required to validate the device within the target population of impaired children and to develop appropriate patient-interface software