Analysis of heart rate variability during acute exposure to moderate altitude and rowing exercise

The present study investigated the effects of acute exposure to moderate altitude and rowing exercises on heart rate variability (HRV). Eleven elite male rowers volunteered to participate in this study (age: 20.7 ± 2.0 yrs; height: 177.5 ± 3.5 cm; weight: 77.0 ± 6.9 kg). Each subject completed one resting measurement in the upright sitting position and two submaximal steady-state exercises (30% and 60% maximal oxygen consumption per minute, V̇O_2max) in random balanced order on a rowing ergometer before, during and seven days after exposure to moderate altitude (2,200-2,600 m). Beat-to-beat HRV was measured continuously during the tests, and the 10 minutes of HRV data were recorded for subsequent analysis. Time and frequency domain analyses of HRV were performed to determine the effects of altitude and exercise. The results demonstrated that the standard deviation of all RR intervals (SDNN) and the square root of the mean squared successive differences between adjacent RR intervals (RMSSD) in sitting position at altitude were significantly lower than before exposure to altitude. There were no significant differences on the time and frequency domain indices in submaximal exercises between altitude and sea level. There were significant differences, however, on the time and frequency domain indices between resting and two submaximal exercises. These results showed that the time domain analysis of HRV could discriminate between the altitude effects on the modulation of the autonomic nervous system, but only in the sitting position and particularly the SDNN and RMSSD indices. HRV analysis could only distinguish the changes of cardiac autonomic modulation between sitting position and exercise.