Respiratory flow (A) and anterioposterior center-of-pressure (B) dynamics were simultaneously recorded over time and compared (C). Empirical mode decomposition was used to decompose each signal into oscillatory modes, each representing the frequency-amplitude modulation of the signal at a specific frequency range (not pictured). The dominant mode of respiration (A, blue line), along with the corresponding mode of the AP COP signal (B, red line), were extracted. Here, for visual purposes, the blue and red curves in panels A and B reflect the dominant modes of each signal summed with all lowerfrequency modes of that signal. The same procedure was repeated for respiratory flow and mediolateral COP fluctuations.