Feasibility of high-intensity interval training in cardiac rehabilitation
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High-intensity interval training (at 85-95% of maximal heart rate) has been found to be a feasible, well-tolerated and time-efficient exercise mode to improve peak oxygen uptake in patients with coronary artery disease, in short term. Most exercise studies, however, are performed during laboratory conditions with strict supervision and monitoring of exercise intensity. In the clinic, the exercise is supervised but with less ability to monitor exercise intensity due to the number of participants attending the group exercise. The overall aim with this thesis was to assess feasibility of high-intensity interval training in both a clinical setting (out-patient cardiac rehabilitation) and as home-based cardiac rehabilitation. Additionally, we wanted to assess long-term exercise adherence following a high-intensity exercise cardiac rehabilitation program. A randomised trial was performed to assess feasibility and effectiveness of a 12 week high-intensity interval training in cardiac rehabilitation in two Norwegian hospitals. Ninety eligible patients with coronary artery disease were included, and randomly allocated to usual care group exercise, treadmill exercise or home-based exercise. Exercise intensity was self-administrated with heart rate monitors, and the participants performed interval training twice a week. The results showed a significant higher increase in peak oxygen uptake in the treadmill group compared to the homebased group, due to better adherence to the training protocol. On treatment analyses, however, revealed equal improvements in peak oxygen uptake in the three groups. Exercise intensity was according to the prescribed exercise intensity in all groups, and drop-out rates were low. Then we performed a one year follow-up study to assess long-term exercise adherence following the high-intensity interval cardiac rehabilitation program. Out of 83 eligible participants, 76 were available for participation. Peak oxygen uptake was significantly elevated above baseline values in all groups after one year. There was a strong trend toward higher levels of physical activity in favour of the home-based group. Finally, a single-group cross-over study was performed to evaluate exercise intensity guidance by rating of perceived exertion during high-intensity interval training group exercise in an out-patient cardiac rehabilitation setting. The study revealed that exercise intensity was below target exercise intensity when guided by rating of perceived exertion. Thus, exercise intensity should be guided by percentage of maximal heart rate using heart rate monitors. In conclusion, this thesis shows that high-intensity interval training is feasible and effective also in a clinical setting or as home-based cardiac rehabilitation. Self-administration of exercise may enhance long-term exercise adherence. Use of percentage of maximal heart rate for exercise intensity guidance induces better achievement of target exercise intensity compared to perceived exertion.