Experimental Studies On The Human Gait Using A Tethered Pelvic Assist Device (T-PAD) Vineet Vashista, S. K. Mustafa and Sunil K. Agrawal Abstract— This paper presents the prototype of a novel tethered pelvic assist device (T-PAD). This is a purely passive device, consisting of a set of elastic tethers with one end attached to a hip brace worn by a subject walking on a treadmill, and the other end attached to a fixed frame surrounding the subject. T-PAD offers the flexibility of varying the assistance required on the pelvis by changing the configuration of the tether attachment locations, number of tethers and tether elasticity. Experimental studies were conducted using a full and a partial pelvic constraint configuration of T-PAD, with varying tether elasticity. The studies were aimed at observing the effect of T-PAD on the human gait. Results show that T-PAD reduced the range-of-motion for the pelvic angles with increase of tether elasticity. However, it had mixed effects on the range-of-motion of the hip angles, but negligible effect on the knee and ankle joint angles. Overall, T-PAD shows potential as a low-cost pelvic support device with pelvic motion control capabilities, and can work in tandem with existing gait trainers. Index Terms— Passive Assistive Device, Pelvis, Human Gait. I. I NTRODUCTION An individual’s quality of life is greatly affected when illnesses or accidents occur that impair the ability to walk. As such, gait training using a treadmill with body weight support (BWS) and manual assistance of the legs and pelvis has become quite common [1], [2]. However, this is very labor intensive and requires therapists to control the motion of the pelvis and the legs (see Fig. 1). Patient Therapist Fig. 1. Traditional gait training involving therapists V. Vashista is a PhD student at the School of Mechanical Engineering, University of Delaware, Newark, DE 19716 <vineet@udel.edu> S. K. Mustafa is a visiting post-doctoral fellow at the School of Mechanical Engineering, University of Delaware, Newark DE 19716 <mustafa@simtech.a-star.edu.sg> * S. K. Agrawal is a Professor at the School of Mechanical Engineering, University of Delaware, Newark, DE 19716 <agrawal@udel.edu> * Corresponding author This subsequently led to the development of robotic gait training devices such as Lokomat, Mechanized Gait Trainer, ARTHuR, HAL, BLEEX, ALEX, GBO and STRING-MAN. However, most of these devices do not control the pelvic motion and merely keep the pelvis suspended by utilizing BWS structures. Studies have shown that the pelvic motion is essential in gait training as it assists in the forward propulsion of the body by transferring forces from the lower extremity to the trunk [3]. It also assists in the swing initiation and modulates the vertical displacement of the body’s center of mass, which is aimed at reducing energy consumption while walking [4]. In view of this shortcoming, there has been recent interests in the rehabilitation community to develop pelvic assist devices. These include KineAssist [5], PAM (Pelvic Assist Manipulator) [6], Walk Trainer [7], and several parallel struc- tured arm designs [8], [9]. While each of these devices have their merits, these are mainly active devices, which are costly due to the hardware setup and control instrumentations. Hence there is a need to develop low cost devices, which can provide support and retain control of the pelvic motion. This paper aims to address this shortcoming and proposes a novel tethered pelvic assist device. The proposed design is a passive system consisting of spring components which are capable of storing mechanical energy. These springs allow modulation of the cartesian stiffness in 6D space, thereby enabling certain control of the pelvic motion. This is safer and more cost-effective compared to active devices. This device also provides full pelvic support, unlike BWS struc- tures, which just provide unilateral support in the coronal plane. The theoretical framework has been reported in the author’s recent work [10], and this paper aims to present the preliminary experimental studies conducted on the developed prototype. The organization of this paper is as follows: Section II presents the conceptual design and salient features of the proposed tethered pelvic assist device. Section III presents the experimental setup of the device, including the equipment used, the frame assignments on the lower limbs to assist in the device evaluation, and the experimental protocol. Section IV presents the experimental results obtained and the observations made. This is followed by the discussion on the potential impact of this device in Section V, and conclusion in Section VI. II. CONCEPTUAL DESIGN OF T-PAD The tethered pelvic assist device (T-PAD) consists of a set of elastic tethers with one end attached to a hip brace