The participants in the intervention group performed a 12-week arm-crank exercise program , 3 sessions/week , consisting of warming-up ( 10-15 min ) followed by a main part in arm-crank ( 20-30 min [ increasing 2 min and 30 seconds each three weeks ] ) at a moderate work intensity of 50-65 % of heart rate reserve ( HRR ) ( starting at 50 % and increasing 5 % each three weeks ) and by a cooling-down period ( 5-10 min ) .