Treadmill Exercise Testing

Treadmill exercise testing was conducted in all the individuals using the modified Bruce protocol. Mason-Likar modification of 12-lead ECG [19] was continuously recorded at a paper speed of 25 mm/s. After the participants had all achieved an exercise time of more than 6 min, and a maximum HR (MHR) of at least 85% of the age-predicted MHR response (peak workload), they spent at least 3 min of recovery without a cool-down period in a sitting position. Exercise capacity was measured in metabolic equivalent levels (METs) at peak exercise. The HRR indices were calculated by subtracting the first-, second- and third-minute HR from the MHR obtained during stress testing and were designated as HRR1, HRR2 and HRR3, respectively. Exercise-onset HR change was calculated by subtracting the resting HR from the HR in the first minute of exercise. The HR reserve was determined by the change in HR from rest to peak exercise during the exercise test. An impaired HRR was described as a decrease in HR from peak exercise to 1 min of recovery of <12 beats per min (bpm) [18].