## 2 Transmissibility of the Acceleration Base
varied among distinct finger locations, vibration frequencies, and applied hand forces. Two major resonances in the vibrational transmissibility were observed [30]. At the first resonance, the vibrations transmitted to different locations were more or less in phase; therefore, this resonance was also observed in the biodynamic response of the driving point, which measured the overall biodynamic response of the system. The second resonance was observed in the fingers. This resonant frequency varied greatly between fingers, as well as between the phalanges of each finger; it was difficult to pinpoint this exact resonance in the biodynamic response of the input point in the system (Figure 2). According to [31], the biodynamic response of the hand can be studied by the grip force in two types of experiments. This kind of study is carried out because vibrations, over time, can lead to occupational diseases related to the hand-arm system, as shown in the specialized literature--in particular, VWF. The first experiment analyzes the transmissibility of vibrations when the grip force is a continuous function, while the hand is subjected to discrete sinusoidal excitations. In the second experiment, the biodynamic responses of the system are studied when the hand is subjected to random vibrations, at broadband frequencies (up to 1500 Hz), measured for five values of grip forces and combinations of grip and push forces. In conclusion, vibration transmissibility depends on the frequencies studied, meaning that they increase with the grip force until reaching a maximum. Next, with the increase in the grip force, which is the internal force exerted by the digits and palm on the manipulated object and depends on the frequency studied, the transmissibility decreases [5]. Figure 2: Laser scanning points on five fingers and the back of the hand [30]. The study in ref. [13] presents a comparison between the vibrations transmitted to the hand and the foot, and it theoretically demonstrates how to stabilize the movement of a mechanical system equivalent to the hand-arm system, subject to vibrations and excited at a frequency of 4.16 Hz. It is known from the specialized literature in this field and reference [4] that, at low frequencies (<25 Hz), changes occur in the normal state of the hand-arm system's functionality, namely disorders of the bones and the nervous system. In conformity with [32], people in an industrial environment can be exposed daily to foot-transmitted vibration (FTV) caused by standing on mobile equipment or vibrating platforms and surfaces (Figure 3). This exposure could increase the risk of developing neurological, vascular, and musculoskeletal problems. In the above study, all results measured for the hand-arm system, namely, HAV and FTV, were compared with the standards. Similarities emerged from the above study between wrist and ankle responses, with the only difference being the resonance area for the fingers and toes. This study stated that HAV standards were more appropriate than whole-body vibration standards for assessing higher-frequency exposure to FTV, in conformity with the standards [5; 6; 7; 8]. In the below image, the green color represents joint points in the hand and toes related to HAV standards, while the red color in the foot is related to FTV exposure in the standards. Based on [33], the reason for the vibrations' transmissibility to the hand is shown in Figures 4-6, alongside the probability of white finger syndrome. FEA (finite-element analysis) and 2D modeling of the hand-arm system were performed, and a laser vibrometer was used for the measurements. Frequencies between 10 and 400 Hz were studied under different grip force levels, and it was found that the addition of a small mass (0.3 g) at the accelerometer did not significantly influence the measurements. Data were collected simultaneously from measurements specific to individuals, including anthropometry.