## 2 Materials and Methods
### Surface Electromyography (sEMG)  
sEMG was recorded using bipolar electrodes (Ambu Neuroline 720 00-S/25, electrode diameter 45 \(\times\) 22, interelectrode distance 2.5 cm, Ambu A/S, Baltorpbakken, Denmark) in 4 muscles: VL, BF, TA, and LG. The electrodes were placed on both legs, according to the international surface EMG for non-invasive assessment of muscles (SENIAM) recommendations [63]. To minimize the impedance (<5 k\(\Omega\)) before the electrodes' application, \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Variable** & **1 st** & **2 nd** & **3 rd** & **4 th** & **5 th** & **6 th** & **7 th** & **8 th** \\  & **Workload** & **Workload** & **Workload** & **Workload** & **Workload** & **Workload** & **Workload** & **Workload** \\ \hline Frequencies (Hz) & 28.9 & 28.9 & 28.9 & 28.9 & 28.9 & 28.9 & 28.9 & 28.9 \\ \hline Displacement (mm) & 0.6 & 0.6 & 0.6 & 0.6 & 0.6 & 0.6 & 0.6 & 0.6 \\ \hline WBV series \(\times\) reps & \(1\times 7\) & \(1\times 8\) & \(2\times 5\) & \(2\times 5\) & \(2\times 5\) & \(2\times 5\) & \(2\times 5\) & \(2\times 5\) \\ \hline WBV duration (s) & 30 & 30 & 30 & 60 & 60 & 60 & 30 & 60 \\ \hline Rest time from reps. (s) & 120 & 60 & 30 & 60 & 60 & 60 & 30 & 60 \\ \hline Rest time from series (s) & / & / & 240 & 180 & 240 & 120 & 160 & 120 \\ \hline Weekly frequency & 2 & 2 & 2 & 3 & 2 & 3 & 3 & 3 \\ \hline Position assumed & High squat & High squat & High squat & High squat & \begin{tabular}{c} High/Half \\ alternation \\ \end{tabular} & \
\begin{tabular}{c} High/Half \\ alternation \\ \end{tabular} & Half squat & Half squat * \\ \hline Total session & 4 & 4 & 32 & 40 & 20 & 14 & 12 & 16 \\ \hline \hline \end{tabular}
\begin{tabular}{c} Abbreviation: whole-body vibration (WBV); repetitions (reps.). * Shifting the body weight from weakest-Leg (30 s) to twtongest-Leg (30 s).  
\end{table} 
Table 1: Workload progression during WBV intervention. Figure 2: (**A**) Body position assumed by the participant on the vibrating platform. (**B**) Relationship between acceleration (dose) and sEMGshots activity (response) of leg muscles. The sEMG activity was recorded in the vastus lateralis (VL), biceps femoris (BF), tibialis anterior (TA), and lateral gastrocnemius (LG) during several trials at different acceleration loads (Isometric or 0, 0.17, 0.29, 1.10, 1.92, 5.70 and 8.43 g (where \(g\) is the Earth’s gravitational field or 9.81 m\(\cdot\)s\({}^{-2}\)). The red square indicates the highest neuromuscular responses (optimal acceleration load) in both legs. the skin was shaved, gently abraded with sandpaper (P320) without producing redness, and cleaned with alcohol. The exact location on the muscle belly was marked to ensure correct sensor positioning across the inter-day EMG recordings. In addition, the electrodes and the modules were fixed with elastic strips (Flexa Elast, Pic Solution, Pikdare S.p.A.) to prevent motion artifacts. The wireless data synchronization unit (MuscleLab 6000, Ergotest-innovation, Porsgrunn, Norway) characteristics were as follows: a built-in radio frequency (RF) module ML6 RFM02 with 2.4 GHz and 1 mW and a typical wireless range in an open space of 20 m. The modules of the MuscleLab characteristics were as follows: RF characteristics of 2.4 GHz, 1 mW; sample rate of 1.2 kHz; high-pass filter of 20 Hz; bandwidth of 20-500 Hz; input signal range of \(\pm\) 5 mVp-p; noise of 14 \(\upmu\)Vp-p (2.2 \(\upmu\)V\({}_{\text{RMS}}\)); and resolution of 0.33 \(\upmu\)V/bit. Utilizing a preamplifier that was situated near the pickup point and directly connected to the electrodes, the raw sEMG signal was amplified and filtered at 1.2 kHz. The frequencies of 20 Hz and 500 Hz were used to band-pass filter the signals using a fourth-order Butterworth filter. The preamplifier's common mode rejection ratio was 100 dB.