Fig. 2: Parametrized frequency analysis of EMG data.

a Power spectral density (PSD) for all neonates (left) and all adults (right) was calculated from rectified EMGs interpolated over the gait cycle (T: stride duration) for each muscle (from top to bottom: BF, RF, LG, and TA, right and left leg muscles were pooled together) using Fast Fourier Transform (FFT) and fitted with an algorithm for parameterizing neural PSDs into periodic and aperiodic components⁴⁶. Gray lines represent fitted PSDs from individual subjects, black lines represent average fitted PSD across subjects, green lines represent the aperiodic component from the individual PSDs, red lines represent the average aperiodic component across subjects. b Periodic component of the PSD for all neonates (left) and all adults (center), black lines represent average across subjects. The average (+SD) number of peaks (defined from the algorithm as the frequency regions of power over and above the aperiodic component) across subjects of each group are illustrated in the right column for each muscle (n = 26 for neonates and n = 30 for adults). c Characteristics of the peaks of the periodic component. The average (+SD) power (left) and bandwidth (right) of the peaks across subjects and muscles are shown on the left side of the panel (n = 344 for neonates and n = 507 for adults). The distributions of the peak power (upper plots, each point represents a peak, all peaks from all muscles of all subjects are pooled together) and of the percent number of peaks across center frequencies of the peaks are shown on the right side of the panel. Note that the great majority (~83%) of the peaks of the periodic component of the EMGs of adults was located near to the stride frequency (1/T) and its first four harmonics (from 2/T to 5/T), while, in neonates, ~17% and ~10% of the peaks were located respectively around 1/T and 2/T and the others peaks were uniformly distributed across frequencies from 0 to 10/T. d Parameters of the aperiodic component. From left to right average (+SD) corrected broadband offset, corrected knee, and exponent of the aperiodic component across subjects and muscles (n = 104 for neonates and n = 120 for adults). Note that all three parameters that characterize the arrhythmic activity of EMGs significantly differ between neonates and adults. e Average (+SD) spectral entropy across subjects for each muscle in neonates and adults (n = 26 for neonates and n = 30 for adults). Data points for all individuals are included in the histograms. Red asterisks denote significant differences between groups (Wilcoxon rank sum test p < 0.05).