## 6 Discussions
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Location** & **Acceleration R.M.S** & **4 h Exposure** & **Years** & **Percent [\%]** \\ \hline \multirow{4}{*}{Hand} & 14 & daily & - & 10 \\  & 2 & daily & - & 30 \\  & 12–28 & daily & 2–5.7 & 10 \\  & \textless{}10 & daily & 2–5.7 & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Exposure over time and probability of VWF symptom appearance [1]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Location** & **Frequency Impedance [Hz]** & **Frequency Power Absorption [Hz]** \\ \hline Fingers & \textless{}40 & \textless{}5–16 \\ Palm & \textgreater{}100 & \textgreater{}60–160 \\ Arm & \textgreater{}25 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Impedance [53] and absorption power of the hand [17]. Regarding the influence of vibrations on the blood system, it can be said that a reduction in the shear forces exerted by the blood on the arterial walls (wall shear stress--WSS) is observed during exposure to vibrations [35; 42; 60] and \"An acute but repeated reduction in WSS can lead to arterial stenosis characteristic of VWF\". Consequently, exposure to high quantities of vibration (>250 Hz), especially high-frequency ones, leads to trans-mission through the hand and further to the elbow, shoulder, and central nervous system, causing visual and audi-tory disturbances over time (Tables 8 and 9). Operators of hand-held power tools are exposed to hand-transmitted vibration and the associated potential injuries. A study showed that an extended arm posture should be avoided when operating hand-held power tools because a large vibration power is absorbed by the human hand--arm system under this conditions, which may cause hand--arm injury [50; 51; 52]. The studies mentioned in [1] led to the emergence of some standards and the establishment of limit and threshold values for hand vibration transmission, specifically for frequencies ranging between 3 and 300 Hz, with the hand positioned on a flat surface. Regarding the perceptibility of hand vibrations, in conformity with [1] and according to [PERSON] and [PERSON] studies in 1974, it was shown that the perceptual sensations of people exposed to vibrations increased with the increase in vibration amplitudes, and they were more pronounced at low frequencies (<40 Hz). These results were obtained by comparing the responses of different people exposed to harmonic and random vibrations, for all three coordinate axes, and the measurements were conducted for the frequency scale from 32 to 2000 Hz. Conclusions were drawn regarding the maximum amplitude of arm swings with the elbow bent at various angles [61] or the hand outstretched. It was also concluded that ambient temperature, time of the work operation, and posture, all influence the transmission of vibrations [54]. The effects of vibrations in the workplace were analyzed by combining stress factors such as vibrations and noises [26]. The results obtained were compared with those of other studies [58; 62; 63] and standardization data. All research studies so far have made valuable contributions regarding vibration transmissibility to hand--arm systems, but what is novel in this paper is the comparison of recent studies to research conducted between the 1980s and 1990s [4]. This paper does not present mathematical models, but only software simulations and experimental analyses given by measurements, in a chronological order. Observations concern the occurrence of Raynaud's syndrome or VWF in the hand, which causes the loss of vibrotactile sensitivity and a reduction in the speed of blood circulation in this appendage, producing an unpleasant condition (tingling) and numbness. Exposure at frequencies greater than 250 Hz has been shown to cause serious medical conditions in the hands. Generally, low frequencies of vibrating tools (<50 Hz) cause vibrations of high amplitudes to be transmitted to the hand [36; 38; 56].