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Lone Schaadt,1,2 Robin Christensen,2 Lars Erik Kristensen,2 Marius Henriksen1,21Department of Physio- and Occupational Therapy, 2The Parker Institute, Copenhagen University Hospital Bispebjerg-Frederiksberg, Copenhagen, DenmarkIntroduction: Intensity of exercise is believed to be a key determinant of response to chronic obstructive pulmonary disease (COPD) rehabilitation. We hypothesized that a higher intensity of exercise, in combination with physiotherapist-led instructions and education in management of breathlessness, would lead to better self-management, possibly delaying calls to the emergency service and preventing hospitalization.Objective: We aimed to test this hypothesis in a subsequent randomized trial, and in order to test study processes and estimate hospitalization rates, we did a small preliminary prospective cohort study on severe COPD patients referred to outpatient rehabilitation.Methods: In 2013, four rehabilitation courses were scheduled (spring, summer, autumn, and winter) each lasting 8 weeks and including eight to ten patients. This preliminary study was designed as a controlled cohort study. The bi-weekly exercise sessions in the spring and autumn courses included a high-intensity walking exercise at 95% of estimated VO2 max for as long as possible. The other two rehabilitation courses included the usual walking exercise intensity (85% of estimated VO2 max). Hospitalization rates were assessed from the participants’ medical records in an 18-month period.Results: We were able to enroll 31 patients in total (15 in the high-intensity exercise group and 16 in regular intensity). There were no group differences in the hospitalization rates. However, during review of the medical records, we observed a striking mortality rate among participants who had attended the high-intensity rehabilitation courses (five deaths) compared to the standard rehabilitation (zero deaths). Four of the five deaths were COPD exacerbations. Fisher’s exact test was statistically significant (P=0.046), as was a log-rank test (P=0.019) of the Kaplan–Meier estimated survival rates.Conclusion: These results from this small preliminary cohort study are alarming and raise concerns about the possible serious risks associated with high-intensity exercise rehabilitation of severe COPD patients.Keywords: Chronic obstructive pulmonary disease, exercise, rehabilitation, mortality