Lower limb movements for clutch-pedal operations were investigated and the influence of four parameters (seat height, pedal travel, pedal travel inclination, pedal resistance) was studied using a multi-adjustable experimental seat. Fifteen subjects participated in the experiment: five short females, five average height males and five tall males. A biomechanical model has been proposed to explain how pedal force direction could be controlled. The experimental observations show that the lower limb movement of clutch pedal operation is mainly guided by the geometric constraints imposed by the task and its environment, especially during the depression phase. The results support the hypothesis that movements obey the principle of minimum work and minimum discomfort. Furthermore, it seems that a functional segmentation exists between the distal joint (ankle) and the proximal joints (knee and hip), thus simplifying the control problem, which is due to the redundancy of the human body. It appears that the depression movement is controlled by proprioceptive feedback related to foot displacement and pedal force, from the fact that the deceleration duration during the depression phase increases with the pedal resistance and pedal travel. The minimum pedal resistance and pedal travel are discussed.

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In order to improve car interior design, data of perceived discomfort and reach posture were collected for 75 different target locations. Altogether, 24 males and females of different statures participated in the experiment. In addition to three-finger grip, index fingertip reach and five finger grip were also compared. The effects of target location, stature and hand grip on reach discomfort were analysed. Predictive regression equations were provided. In addition to the confirmation of target location effects, the results showed that seat back and steering wheel affected discomfort. Their effects differed according to the subject's anthropometry. A detailed analysis of possible interference between the car interior and reach movement showed that short females were more likely impeded by the seat back when a target was close to the body. A significant difference between three hand grip types could be explained by the change of hand reach distance when changing hand grip type. STATEMENT OF RELEVANCE: The present study analysed the effects of target location, stature and hand grip type on reach discomfort, based on the statistical analysis of subjective ratings when reaching a target in a vehicle. The results would help to optimise the location of automotive controls for improving car interior design.

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