  In order to assess fatigue independent amplitude-frequency correlations in
EMG signals we asked nineteen male subjects to perform a series of isometric
muscular contractions by extensors of the knee joint. Different amplitudes of
the signal were due to randomly varying both the joint moment and the overall
amplification factor of the EMG apparatus. Mean and median frequency, RMS and
mean absolute value were calculated for every combination of joint moment and
amplification at the original sampling rate of 5 kHz and at several simulated
lower sampling rates. Negative Spearman and Kendall amplitude-frequency
correlation coefficients were found, and they were more pronounced at high
sampling rates.
