Ultrafast ultrasound imaging can be used to access single motor units in deep muscles, but the underlying biomechanical source remains to be understood.

Finding the reflex circuitry responsible for high-frequency vibration-induced muscle contraction takes work. The main challenge is to determine the effective stimulus time (EST) point at which continuous (sinusoidal) stimulation (i.e., vibration) triggers the reflex response. A novel “cumulated averaging method” has been previously proposed for estimating the EST point. In the current study, we aimed to test the reliability of the cumulated average method. We used five different whole-body vibration (WBV) frequencies in two experiments. The consistency between the EST points estimated from the first and second experiments was analysed with the intraclass correlation (ICC) and technical error of measurement (TEM). The ICC coefficient with 95% CI for the EST point estimation was 0.988 (0.950–0.997). The relative TEM was 1.3%. We concluded that the cumulated average method is highly reliable in estimating the effective stimulus time point for high-frequency continuous sinusoidal signals.