The present study dealt with energy consumption during gait with Intelligent Prosthetic Knee Joint (NI-C111, NABCO, Japan) which is capable of electrically and automatically changing the joint stiffiless by adjusting the opening of the air cylinder valve for different gait speed. The joint was attached to the left knee of a normal subject as an amputee model. Kinematic and kinetic data were obtained from the subject, while walking at the speed of 3, 4.5, and 6 km/h, with narrow, neutral, and wide valve openings. A mathematical analysis was performed to obtain the integral of joint power with time in the contralateral normal leg during stance phase. For each speed, there was an optimal valve opening which gave minimal energy consumption. At the speed of 6 km/h, the energy consumption was lower with the above-mentioned joint than with Total Knee Prosthesis (TK2000, Century XXII lhnovations, USA).

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