Abstract
Heart Rate Variability (Atlaoui et al.) is greater in aerobically trained athletes due to an increase in parasympathetic tone. While high levels of aerobic training are generally associated with good cardiovascular responsiveness, it sometimes leads to suppressed responsiveness. To examine the cardiovascular and autonomic changes that occur in trained and untrained subjects exposed to hypoxic (H) and normoxic (N) conditions. Seven aerobically trained men (6 trained cyclists, 1 runner; age: 29.14 + 4.37 yrs, height: 72.1 + 2.1 in, weight: 77.9 + 7.2 kg, average training hours/week 14.6 + 4.35) and 6 untrained men (age: 28.3 + 4.8 yrs, height: 69.41 + 3.0 in, weight 81.43 + 16.9 kg) were recruited for this study. This study used a double-blind crossover design and subjects were randomly assigned treatment order. Subjects rested for one hour and EKG (Hexoskin) was recorded as well as SaO2. After one hour BP was taken. Subjects then completed a submaximal exercise bout (1.5 watts/Kg BW) for 10 minutes. Subject then reported back to lab for a second test to receive the opposite treatment. Standard deviation of normal-to-normal interval (SDNN) was calculated for each subject during rest and exercise for each environmental treatment. HRV, BP, HR, and SaO2 were analyzed using a Wilcoxon test of Correlated Groups and a Mann-Whitney U test for the difference between two independent samples. An alpha level of 0.05 was used for significance. Trained subjects had a trend (significant at 0.1 level) towards an ANS mediated response (N: 17.57 + 16.6 ms, H: 8.14 + 6.2 ms), while UT subjects did not change during exercise in different environments. Untrained subjects had a significant increase in HR during the exercise bout in hypoxia when compared to that of the normoxic bout (N: 139.2 + 26.1bpm, H: 151.5 + 28.4 bpm) when the trained group did not significantly differ between environments (N: 101.6 + 23.1 bpm, H: 112.8 + 20.9 bpm). Trained subjects had a significant increase in BP in the hypoxic bout of exercise (N: 143.3 + 10.8 mmHg, H: 150.3 +15.8 mmHg) while the untrained subjects did not (N: 155.3 + 9.4 mmHg, H: 159 + 15.7 mmHg). Trained subjects may be more sensitive to small changes in autonomic stimuli whereas Untrained subjects are not as sensitive to change. Both groups were found to be equally responsive to strong autonomic stimuli.