## 1 Introduction  
Japan has become a super-aging society, where people aged over 65 years old account for 28.4% of the population [1]. Falls and fractures during walking decrease the ability to walk [1]; therefore, they should be prevented in older people. A risk factor for falls in the elderly is stumbling during walking [2]. Stumbling occurs because of the large variability and low height of foot clearance during the swing phase [3, 4, 5]. Foot clearance is mainly controlled by hip and knee flexion movements [6]. Older adults have significantly smaller knee flexion angles than younger adults [7]. Furthermore, stroke patients have small hip and knee flexion angles [8]. Thus, there is a need to increase the hip and knee flexion angles during the swing phase to decrease the risk of stumbling.  
Recently, robotic gait rehabilitation has been shown to be useful in people with paralysis and muscle weakness [9, 10]. Robotic devices can realize powerful assistance of joint motions through the generation of a large torque. This type of rehabilitation has achieved significant improvements in speed [9], joint angles [11], and muscle activity [12] during walking. However, these devices have disadvantages, such as difficulty in wearing,high cost, large weight, and limited availability. In addition, a physical therapist must be nearby to assist with the wearing and operation of the robotic devices.  
Wearable assistive devices have also been developed for gait rehabilitation. The pneumatic artificial muscle (PAM) is a useful actuator for such devices [13]. Although the PAM cannot generate a large assistive torque, it has certain benefits, such as low cost, small weight, and flexibility [14]. Thus, the PAM can support lower limb joint motions during walking [13; 15; 16; 17; 18].  
In previous studies [13; 17], constant contraction parameters have been employed for individuals in assisting with the hip flexion motion during the swing phase. However, the temporal parameters for maximizing the hip flexion angle may differ among individuals. Consequently, we have developed a PAM driver system that can change the delay of contraction from the trigger, as well as the contraction duration, through a smartphone [19; 20]. By realizing the control of the PAM through a smartphone, the users can wear the PAM by themselves, and the therapist can tune the parameters from a distance. Using this system, the hip and knee flexion angles of healthy young adults in their 20s can be significantly increased compared to the angles without the PAM assistance with individual differences in the parameter settings [14].  
However, no study has reported the effectiveness of swing assist using a PAM driver system for the hip and knee joint motions of the elderly. Elderly people have a low walking ability and different temporal and kinematic characteristics of gait, compared with those of young people [7; 21; 22]. In addition, the elderly experience functional decline with aging and low balance capacity [23]. Consequently, it is unclear whether the parameter settings for maximizing the hip flexion angle are the same for the elderly those of the young population; the elderly may differ from younger people in their responsiveness to the PAM assistance. To clarify the effectiveness of swing assist using our PAM driver system and the characteristics of its effect for the elderly, it is necessary to evaluate its assisting effect in the elderly.  
This study examined the parameter settings for maximizing the hip flexion angle in elderly subjects. Additionally, it evaluated the effect of swing assist using a PAM driver system on the hip and knee joint angles during the swing phase and gait performance.