Time-frequency analysis during continuous incremental isometric exercise

Few authors have used spectral analysis of heart rate variability to characterize cardiovascular control mechanisms during isometric exercise. This technique requires stationary signals and long exercise protocols for different loads, using at least three minutes per load. In this work we explore the use of cardiovascular time-variant spectral indexes during a continuous incremental isometric exercise protocol. We studied the effect of three exercise loads for isometric one leg-knee extension on cardiovascular response. Two respiratory conditions, spontaneous and controlled breathing, were evaluated. Born-Jordan time-frequency distribution was used to estimate time-variant power spectra from RR intervals, systolic pressure and breathing series. The use of time-variant analysis allowed us to quantify cardiovascular spectral indexes and to discriminate among three continuous exercise loads using a very short-term protocol of isometric exercise