Selective discrete Fourier transform algorithm for time-frequency analysis: method and application on simulated and cardiovascular signals

Heart rate variability is related to training load variables in interval running exercises

“…The chosen frequency components can limit the frequency resolution, as the duration of the time-window should be at least five times the lowest analyzed wavelength (Keselbrener & Akselrod, 1996). Digital filtering can be used to remove frequency components out of interest from the time series, especially useful in analysis of HR signal consisting of two separate frequency components, thus diminishing cross-terms and helping to improve the quality of the signal.…”

“…Since the RRI time series were not stationary during the recovery after exercises, the traditional spectral analysis could not be used for HRV analysis. Therefore, the short-time Fourier transform (STFT) method, an extension of FFT, was used for HRV time-frequency analysis (Elsenbruch et al 1999;Keselbrener & Akselrod, 1996).…”

“…The time and frequency resolutions of STFT are inversely related, and therefore the chosen resolutions are result of a compromise. It is recommended that the duration of the time window is five times of the slowest analyzed wavelength (Keselbrener & Akselrod, 1996). In order to obtain a high enough time resolution, a relatively short window was chosen for study I.…”

“…orthostatic test, exercise and recovery. It has been found to detect transient changes in vagal activity (Keselbrener & Akselrod, 1996;Martinmäki et al 2006a), which has given an opportunity to investigate the pattern of rapid HRV changes immediately after exercise cessation. During exercise, HRV is significantly decreased, as sympathetic nervous activity is augmented and vagal activity attenuated.…”

“…It is known that both tidal volume and breathing frequency may affect high frequency component of HRV at rest. Increased tidal volume has been found to increase HRV, whereas increased breathing frequency decreases it (Grossman et al 1991;Keselbrener & Akselrod 1996). However, Bartels et al (2004) suggested that HFP during exercise presents true cardiovascular vagal modulation instead of being affected by changes in ventilation.…”