We examined the transfer function of autonomic heart rate (HR) control in anesthetized sedentary and exercise trained (16 weeks, treadmill for 1 h, 5 times/wk at 15m/min and 15° grade) rats for comparison to HR variability assessed in the conscious resting state. The transfer function from sympathetic stimulation to HR response was similar between groups (gain, 4.2 ± 1.5 vs. 4.5 ± 1.5 beats min−1 Hz−1; natural frequency, 0.07 ± 0.01 vs. 0.08 ± 0.01 Hz; damping coefficient, 1.96 ± 0.55 vs. 1.69 ± 0.15; and lag time, 0.7 ± 0.1 vs. 0.6 ± 0.1 s, sedentary vs. exercise trained, respectively, mean ± SD). The transfer gain from vagal stimulation to HR response was 6.1 ± 3.0 in the sedentary and 9.7 ± 5.1 beats min−1 Hz−1 in the exercise trained group (P = 0.06). The corner frequency (0.11 ± 0.05 vs. 0.17 ± 0.09 Hz) and lag time (0.1 ± 0.1 vs. 0.2 ± 0.1 s) did not differ between groups. When the sympathetic transfer gain was averaged for very low frequency (VLF) and low frequency (LF) bands, no significant group effect was observed. In contrast, when the vagal transfer gain was averaged for VLF, LF, and high frequency bands, exercise training produced a significant group effect (P < 0.05 by two-way repeated measures ANOVA). These findings suggest that, in the frequency domain, exercise training augments the dynamic HR response to vagal stimulation but not sympathetic stimulation regardless of the frequency bands.
- exercise training
- heart rate variability
- transfer function
- systems analysis
- Copyright © 2010, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology