EN
Aim of the work was to verify if the sinusoidal modulation of the stimulation rate of individual rat MUs may provide reliable sinusoidal responses of the recorded force with an acceptable harmonic distortion (HD). After MU classification, the isolated axons of the spinal ventral roots were electrically stimulated with rates sinusoidally changing, from a minimum to a maximum value, with different frequencies of modulation for slow (0.4–1.0–2.0–4.0 Hz) and fast (1.0–2.0–4.0–7.0 Hz) MUs. From the twitching raw signal an interpolated force curve was obtained for each frequency to generate, from the sample by sample difference with the theoretical sine, the specific error signal. At each input frequency, HD was calculated as the percentage ratio between the total power of the error signal and the total power of the theoretical sine. Nine MUs, characterized as S (n=3), FR (n=3) and FF (n=3), were studied. The range of HD for S, FR, FF units was 0.9–5.1%, 0.3–3.5%, 0.3–4.1%, respectively. These HD values indicate that the sinusoidal responses of muscle functional unit were reliable and further suggest the possibility to use this method for single MU transfer function identification.