Concentric and Eccentric Pedaling-Type Interval Exercise on a Soft Robot for Stable Coronary Artery Disease Patients: Toward a Personalized Protocol

Abstract

Background: Cardiovascular diseases are the leading causes of death worldwide, and coronary artery disease (CAD) is one of the most common causes of death in Europe. Leading cardiac societies recommend exercise as an integral part of cardiovascular rehabilitation because it reduces the morbidity and mortality of patients with CAD. Continuous low-intensity exercise using shortening muscle actions (concentric, CON) is a common training modality during cardiovascular rehabilitation. However, a growing clinical interest has been recently developed in high-intensity interval training (HIIT) for stable patients with CAD. Exercise performed with lengthening muscle actions (eccentric, ECC) could be tolerated better by patients with CAD as they can be performed with higher loads and lower metabolic cost than CON exercise.

Objective: We developed a clinical protocol on a soft robot to compare cardiovascular and muscle effects of repeated and work-matched CON versus ECC pedaling-type interval exercise between patients with CAD during cardiovascular rehabilitation. This study aims to ascertain whether the developed training protocols affect peak oxygen uptake (VO_2peak), peak aerobic power output (P_peak), and parameters of muscle oxygen saturation (SmO₂) during exercise, and anaerobic muscle power.

Methods: We will randomize 20-30 subjects to either the CON or ECC group. Both groups will perform a ramp test to exhaustion before and after the training period to measure cardiovascular parameters and SmO₂. Moreover, the aerobic skeletal muscle power (P_peak) is measured weekly during the 8-week training period using a simulated squat jump and a counter movement jump on the soft robot and used to adjust the training load. The pedaling-type interval exercise on the soft robot is performed involving either CON or ECC muscle actions. The soft robotic device being used is a closed kinetic chain, force-controlled interactive training, and testing device for the lower extremities, which consists of two independent pedals and free footplates that are operated by pneumatic artificial muscles.

Results: The first patients with CAD, who completed the training, showed protocol-specific improvements, reflecting, in part, the lower aerobic training status of the patient completing the CON protocol. Rehabilitation under the CON protocol, more than under the ECC protocol, improved cardiovascular parameters, that is, VO_2peak (+26% vs -6%), and P_peak (+20% vs 0%), and exaggerated muscle deoxygenation during the ramp test (248% vs 49%). Conversely, markers of metabolic stress and recovery from the exhaustive ramp test improved more after the ECC than the CON protocol, that is, peak blood lactate (-9% vs +20%) and peak SmO₂ (+7% vs -7%). Anaerobic muscle power only improved after the CON protocol (+18% vs -15%).

Conclusions: This study indicates the potential of the implemented CON and ECC protocols of pedaling-type interval exercise to improve oxygen metabolism of exercised muscle groups while maintaining or even increasing the P_peak. The ECC training protocol seemingly provided a lower cardiovascular stimulus in patients with CAD while specifically enhancing the reoxygenation and blood lactate clearance in recruited muscle groups during recovery from exercise.

Trial registration: ClinicalTrials.gov NCT02845063; https://clinicaltrials.gov/ct2/show/NCT02845063.

Keywords: cardiovascular rehabilitation; concentric and eccentric exercise; high-intensity interval training; muscle oxygen saturation; near-infrared spectroscopy; peak oxygen uptake; ramp test; skeletal muscle power; soft robot.

Figure 1

The study design timeline. CON: concentric protocol; ECC: eccentric protocol; PRE: before training period; POST: after training period; VO_2peak: peak oxygen uptake; P_peak: peak aerobic power output; HR: heart rate; BP: blood pressure; BL: blood lactate; NIRS: near-infrared spectroscopy; SmO₂: muscle oxygen saturation.

Figure 2

Moxy monitor placement.

Figure 3

Top: Display of the audiovisual feedback to control training on the soft robot. Bottom: Timeline for the progressive increase of training volume and intensity for the CON and ECC protocol, respectively. ROM: range of motion; CON: concentric protocol; ECC: eccentric protocol; P_peak: peak power output (Source: Daniel Fitze, Dynamic Devices AG).

Figure 4

Left: Display of the visual feedback during the Real Power test on the soft robot. Blue and red lines, the knee joint flexion angle of the left and right leg versus time. Right: Display of the visual feedback during the Reactive Power test on the soft robot (source: Daniel Fitze, Dynamic Devices AG).

Figure 5

The representative example of the SmO₂ course during the ramp test of a healthy subject including raw data, processed data, and different parameters. SmO₂: muscle oxygen saturation; t: time; min: minimum; max: maximum.

Figure 6

Training-induced changes of cardiorespiratory parameters in the first 2 patients completing the CON or ECC protocols. Bar graph of the percentage changes after versus before the training period (ie, POST vs PRE). VO_2peak: peak oxygen uptake; P_peak: peak aerobic power output; HR_peak: peak heart rate; Sys BP_peak: peak systolic blood pressure; Dia BP_peak: peak diastolic blood pressure; BL_peak: peak blood lactate concentration.

Figure 7

Training-induced changes of SmO₂ parameters in the first 2 patients completing the respective CON or ECC protocols. Bar graph of the percentage changes POST versus PRE. SmO₂: muscle oxygen saturation; t: time; min: minimum; max: maximum.

Figure 8

Training-induced changes of the muscle performance on the soft robot for patients completing the respective CON or ECC protocols. Bar graph of the percentage changes POST (after the training period) versus PRE (before the training period). CON: concentric protocol; ECC: eccentric protocol; Avg: average; t_peak: time to peak.