Identifier

etd-1108101-143050

Degree

Doctor of Philosophy (PhD)

Department

Kinesiology

Document Type

Dissertation

Abstract

The purpose of this investigation was to determine if 8 exercise endurance training (ET) sessions over 2 weeks significantly alters cardiac autonomic modulation, as measured by heart rate variability (HRV). Twenty-four college-aged males were recruited for this study and were randomized into either an exercise group (EX; n=12) or a control group (CT; n=12). EX underwent 2 weeks of ET on a cycle-ergometer (frequency: four times/week; duration: 40 minutes; intensity 80-85% HRreserve), whereas CT was instructed not to alter their previous level of physical activity. Five-minute ECG tracings were collected for HRV under the following conditions: 5 minutes of paced breathing at a frequency of 12 breaths/minute (PB), 5 minutes of spontaneous breathing (SB1), 5 minutes of 70-degree head-up tilt on a tilt table (TILT), and a second 5-minute period of spontaneous breathing (SB2). The data were collected on 5 occasions (Test 1-Test 5) during a 2-week period. HRV was reported as the standard deviation of RR intervals, and as normalized units (NU) of the natural logarithm of high- and low-frequency power (lnHF and lnLF). A mixed-model analysis of variance (ANOVA) with repeated measures was used to evaluate any Group X Time interaction, or main effects of Group or Time on HRV. Alpha was set at 0.05. EX exhibited a significant increase in peak oxygen consumption (8%), whereas this parameter was unchanged in CT. During PB, ANOVA revealed a Group X Time interaction such that EX exhibited decreases in lnLFNU (2.89 vs. 3.45 ln%) and lnLF/lnHF (0.82 vs. 0.90) during Test 5 compared to Test 1, while there were no such differences across time in CT. Additionally, there was a Group X Time interaction during TILT such that EX exhibited lower lnLFNU (4.12 vs. 4.42 ln%) and lnLF/lnHF (1.12 vs. 1.46), and greater lnHFNU (3.52 vs. 2.53 ln%) during Test 5 compared to Test 1, while these indices were unchanged across time in CT. These data suggest that 8 ET sessions over 2 weeks increases vagal modulation of the heart. Furthermore, these data suggest that it takes at least 8 ET sessions to induce such changes.

Date

2001

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Robert H. Wood

Included in

Kinesiology Commons

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