Division of Mechanical Engineering, Department of Engineering and Information Technology, Institute for Rehabilitation and Performance Technology, Bern University of Applied Sciences, 3400, Burgdorf, Switzerland.
Department of Rehabilitation Medicine, Srinagarind Hospital and Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
Biomed Eng Online. 2018 Sep 24;17(1):128. doi: 10.1186/s12938-018-0561-x.
Heart rate variability (HRV) arises from the complex interplay of sympathetic and parasympathetic autonomic regulation of heart rate. Ultra-low frequency (ULF) and very-low frequency (VLF) components of HRV play a crucial role in automatic HR controllers, but these frequency bands have hitherto largely been neglected in HRV studies. The aim of this work was to investigate changes in ULF and VLF heart rate variability with respect to exercise intensity and time during treadmill running.
RR intervals were determined by ECG in 21 healthy male participants at rest, and during moderate and vigorous-intensity treadmill running; each of these three tests had a duration of 45 min. Time dependence of HRV was investigated for moderate and vigorous running intensities by dividing the constant-speed stages into three consecutive windows of equal duration ([Formula: see text] 14 min), denoted [Formula: see text], [Formula: see text] and [Formula: see text]. ULF and VLF power were computed using Lomb-Scargle power spectral density estimates.
For both the ULF and VLF frequency bands, mean power was significantly different between the resting, moderate and vigorous intensity levels (overall [Formula: see text]): mean power was lower for moderate vs. rest ([Formula: see text]), for vigorous vs. rest ([Formula: see text]), and for vigorous vs. moderate ([Formula: see text]). For both ULF and VLF and moderate intensity, mean power was significantly different between the three time windows (overall [Formula: see text] for ULF, overall [Formula: see text] for VLF): for ULF, mean power was lower for [Formula: see text] vs. [Formula: see text] ([Formula: see text]) and for [Formula: see text] vs. [Formula: see text] ([Formula: see text]); for VLF, mean power was lower for [Formula: see text] vs. [Formula: see text] ([Formula: see text]). For ULF and vigorous intensity, there was no significant difference in mean power between the three time windows (overall [Formula: see text]). For VLF and vigorous intensity, mean power was significantly different between [Formula: see text], [Formula: see text] and [Formula: see text] (overall [Formula: see text]): mean power was lower for [Formula: see text] vs. [Formula: see text] ([Formula: see text]) and for [Formula: see text] vs. [Formula: see text] ([Formula: see text]).
The degree of HRV in terms of ULF and VLF power was found to decrease with increasing intensity of exercise. HRV was also observed to decrease over time, but it remains to clarify whether these changes are due to time itself or to increases in HR related to cardiovascular drift. For feedback control applications, attention should be focused on meeting performance targets at low intensity and during the early stages of exercise.
心率变异性（HRV）源于心率的交感和副交感自主调节的复杂相互作用。HRV 的超低频（ULF）和极低频（VLF）分量在自动 HR 控制器中起着至关重要的作用，但迄今为止，这些频段在 HRV 研究中基本上被忽视了。本研究旨在探讨在跑步机跑步过程中，运动强度和时间对 ULF 和 VLF 心率变异性的影响。
21 名健康男性参与者在静息、中强度和高强度跑步机运动时，通过心电图确定 RR 间期；这三种测试的持续时间均为 45 分钟。通过将恒速阶段分为三个连续的等时长窗口（[Formula: see text]分钟），即[Formula: see text]、[Formula: see text]和[Formula: see text]，研究中强度和高强度跑步的 HRV 时间依赖性。使用 Lomb-Scargle 功率谱密度估计计算 ULF 和 VLF 功率。
对于 ULF 和 VLF 两个频段，静息、中强度和高强度三个水平之间的平均功率均有显著差异（总体[Formula: see text]）：中强度与静息相比（[Formula: see text]），高强度与静息相比（[Formula: see text]），以及高强度与中强度相比（[Formula: see text]），平均功率均较低。对于 ULF 和 VLF 以及中强度，三个时间窗口之间的平均功率均有显著差异（总体[Formula: see text]）：对于 ULF，[Formula: see text]与[Formula: see text]相比（[Formula: see text]），[Formula: see text]与[Formula: see text]相比（[Formula: see text]），平均功率均较低；对于 VLF，[Formula: see text]与[Formula: see text]相比（[Formula: see text]），平均功率较低。对于 ULF 和高强度，三个时间窗口之间的平均功率无显著差异（总体[Formula: see text]）。对于 VLF 和高强度，[Formula: see text]、[Formula: see text]和[Formula: see text]之间的平均功率有显著差异（总体[Formula: see text]）：[Formula: see text]与[Formula: see text]相比（[Formula: see text]），[Formula: see text]与[Formula: see text]相比（[Formula: see text]），平均功率均较低。
以 ULF 和 VLF 功率表示的 HRV 程度随着运动强度的增加而降低。随着时间的推移，HRV 也观察到降低，但仍不清楚这些变化是由于时间本身还是由于与心血管漂移相关的心率增加所致。对于反馈控制应用，应注意在低强度和运动早期满足性能目标。
