###### Abstract  
The accelerator pedal in a vehicle can be pressed by either of two (natural and rotated) foot postures, according to driver preference. Since the rotated foot posture requires only foot motion to switch between the brake and accelerator pedals, most drivers prefer it over the natural foot posture, which requires both leg and foot motions to switch between the pedals. However, the rotated foot posture may require more leg-muscle efforts and an awkward foot posture while operating the accelerator pedal, due to an inappropriate contact between the sole of the foot and the top surface of the accelerator pedal. This study examined the effects of foot postures on leg-muscle activities and foot angles while pressing the accelerator pedal for 10 male drivers. The experimental data revealed that %MVC (maximum voluntary contraction) of leg muscles for the rotated posture (6.39%) was significantly higher than that of the natural posture (3.86%). Both foot postures showed shared patterns in foot angles while pressing the accelerator pedal; however, a slight awkward foot inversion was observed in the rotated posture while pressing the accelerator pedal. The findings of this study suggest that a new design of accelerator pedal is needed for a better user experience while pressing the accelerator pedal with the rotated foot posture. d 2  
The pendulum type of accelerator pedals mostly used in the aforementioned previous studies has been replaced with the organ type, which has better usability. The pendulum type is suspended on the car body using mechanical linkages [7; 8; 9; 10; 11] and was widely adopted in sedans. The pendulum type of accelerator pedal is designed to ease the driver into the movement of his/her foot from the brake pedal to the accelerator pedal, and vice versa. In addition, it facilitates the easy release of the accelerator without excessive discomfort in the ankle. However, it might be harder to control during sudden action, because of the different trajectories of the accelerator pedal and the natural foot-pressing motion. Due to its disadvantages in usability and simplicity, the organ type is gradually replacing the pendulum type. Since the organ type is placed on the floor of the car [7; 11], it allows the driver's foot and the pedal to follow the same moving path when being pressed. It also enables the easy control of the accelerator pedal, and is more comfortable to use over a long period, due to the fact that it stabilizes the driver's heel position on the floor [7; 12]. In addition, the organ type can facilitate drive-by-wire technologies, which can detect the pressed position of the pedal using an accelerator position sensor [13; 14]. The organ type allows the driver two different foot postures (natural vs. rotated) in operating the accelerator pedal. The driver can employ the natural foot posture (Figure 1a), which lifts off his/her right foot from the brake pedal and moves the foot toward the accelerator pedal. Although this posture can cause more muscle efforts in moving the right foot (including the leg) from the brake pedal to the accelerator pedal, it allows the driver to comfortably press the accelerator pedal with a comfortable foot posture. On the other hand, the rotated foot posture requires the driver to rotate the right foot around the heel toward the accelerator pedal (Figure 1b). This posture has an advantage in easily switching the pedals without large movement of the leg; however, there might be an inappropriate contact between the sole of the foot and the top surface of accelerator pedal, due to their misalignment. This may require more leg muscle efforts, due to imperfect contact while operating the accelerator pedal. Operation of car pedals requires an intensive use of the leg and foot, which can cause discomfort and/or fatigue for a prolonged driving period [15; 16]. The frequent and repetitive movements may result in musculoskeletal burdens of the lower limb.