Department of Technical Informatics, University of Szeged, 6720, Szeged, Hungary.
Sci Rep. 2024 Jan 31;14(1):2604. doi: 10.1038/s41598-024-52905-8.
The scale-free nature of daily human activity has been observed in different aspects; however, the description of its spectral characteristics is incomplete. General findings are complicated by the fact that-although actigraphy is commonly used in many research areas-the activity calculation methods are not standardized; therefore, activity signals can be different. The presence of 1/f noise in activity or acceleration signals was mostly analysed for short time windows, and the complete spectral characteristic has only been examined in the case of certain types of them. To explore the general spectral nature of human activity in greater detail, we have performed Power Spectral Density (PSD) based examination and Detrended Fluctuation Analysis (DFA) on several-day-long, triaxial actigraphic acceleration signals of 42 healthy, free-living individuals. We generated different types of activity signals from these, using different acceleration preprocessing techniques and activity metrics. We revealed that the spectra of different types of activity signals generally follow a universal characteristic including 1/f noise over frequencies above the circadian rhythmicity. Moreover, we discovered that the PSD of the raw acceleration signal has the same characteristic. Our findings prove that the spectral scale-free nature is generally inherent to the motor activity of healthy, free-living humans, and is not limited to any particular activity calculation method.
人类日常活动的无标度性质已在不同方面得到观察；然而，其谱特征的描述并不完整。一般发现由于以下事实而变得复杂：尽管活动记录仪在许多研究领域中被广泛使用，但活动计算方法并未标准化；因此，活动信号可能不同。活动或加速度信号中 1/f 噪声的存在主要在短时间窗口中进行分析，并且仅在某些类型的情况下才检查了完整的光谱特征。为了更详细地探索人类活动的一般光谱性质，我们对 42 名健康、自由生活的个体的数天三轴活动记录仪加速度信号进行了基于功率谱密度（PSD）的检查和去趋势波动分析（DFA）。我们使用不同的加速度预处理技术和活动指标从这些信号中生成了不同类型的活动信号。我们发现，不同类型的活动信号的频谱通常遵循一种通用特征，包括高于昼夜节律性的频率上的 1/f 噪声。此外，我们发现原始加速度信号的 PSD 具有相同的特征。我们的发现证明了无标度谱性质普遍存在于健康、自由生活的人类的运动活动中，并且不受任何特定的活动计算方法的限制。
