## 1 Introduction  
Power seats (i.e., electrically adjustable seats that can move in several ways) with electrical control, for example, electrical backrest adjustment, are widely used in airplanes, vehicles, and offices for safety, convenience, and comfort. The speed of moving seat components, for example, the backrest and the seat pan, during an adjustment can influence subjective preference for a seat and could be related to the overall comfort of a seat [1]. In contrast to \"comfort\", \"discomfort\" is commonly used to describe subjective reactions (e.g., annoying, uncomfortable, and distressed) to environmental stresses, mainly associated with pain, tiredness, soreness, and numbness [2, 3, 4]. Discomfort can be influenced by changing the state of seat components, for example, varying the incline angle of a backrest affects posture and human-seat interface pressure, and therefore further influences a subjective evaluation of discomfort [2, 3, 4]. [PERSON] and [PERSON] conducted a subjective evaluation of seat discomfort through a survey and an objective evaluation of seat discomfort by measuring human-seat interface pressure; they established a multiple linear regression relation between subjective and objective results. [PERSON] reported that the best way to obtain feedback about perception of comfort was through the administration of a questionnaire [5, 6]. The inclination of a backrest significantly affects an occupant's static comfort, and many studies have been conducted to determine the most appropriate angle for static comfort [1, 7, 8, 9]. [PERSON] and [PERSON] [7] asked subjects to complete typing tasks in different sitting postures and concluded that different sitting postures as a result of different backrest angles (100\({}^{\circ}\), 125\({}^{\circ}\), and 160\({}^{\circ}\)) and seat tilt angles (5\({}^{\circ}\) and 40\({}^{\circ}\)) led to significant differences in typing performance and comfort. [PERSON] and [PERSON] [9] indicated that seat discomfort decreased with an increase in backrest angle. [PERSON] and [PERSON] [8] failed to find a significant difference in comfort between different seat inclination conditions, but they proposed that an inclined backrest (cushion padding and degree of fit at the shoulder, middle back, and lower back) had a strong correlation with the overall comfort. Generally speaking, backrest angles affect body-seat interface pressure variables, for example, the average pressure, peak pressure, and contact area, and therefore influence the overall discomfort eventually [4; 10; 11; 12]. Backrest inclination can also lead to various kinds of local discomfort affecting different body parts, i.e., the pressure distribution of the body-seat interface. Usually, higher pressure on body parts implies greater discomfort [13]. [PERSON] and [PERSON] [14] indicated that the lumbar region supported more weight when the seat was tilted, since the center of the pressure distribution was shifted back to the ischial tuberosity. However, follow-up studies found that pressure on the buttocks and ischial tuberosity decreased, whereas pressure on the back region increased when the seat or the backrest was tilted [15; 16]. [PERSON] and [PERSON] [17] found that the pressures increased at the sacrococcygeal and decreased at the ischial tuberosity with increasing backrest tilt angle. [PERSON] and [PERSON] [9] indicated that backrest inclination affected the human-seat interface's pressure distribution (including the seat pan and the backrest) by changing the sitting posture or muscle activation. The inclination of the backrest affects the dynamic discomfort of an occupant, along with magnitude, frequency, direction, and location of the vibration. The perception thresholds of vibration have been shown to significantly depend on the backrest inclination at a low frequency when the direction of vibration was normal to the back in the \(x\)-axis of the body [18].