Powered orthoses are leading to an imminent change in the field of assistance. The major challenges faced by the technology concern the management of the interaction between the user and the wearable device and the coordination between the user intention and the actuated motion. In the present study, we used the HiBSO (Hip Ball-Screw Orthosis) to investigate the contribution of an assistance to the hip flexion/extension motion during walking. Four healthy subjects wearing the HiBSO performed a controlled walking at 3.6 km/h on a treadmill. Three conditions were evaluated: free walking (without orthosis), a transparent mode (orthosis providing no assistance) and an assistive mode (orthosis assisting 10% of walking torque). Kinematics tracking and heart rate recording have been used for the assessment of the assistance. The observations exhibited a clear influence of the assistance on the hip flexion velocity during the swing phase. The ranges of motion of the hip and the knee tend to increase in the assistive mode whereas the ankle range of motion is reduced. Thus the assistance of the hip has a global influence on all the joints. The heart rate acquisitions demonstrated a higher energy expenditure while wearing the orthosis in both transparent and assistive mode.