Knee extensors play a key role in maintaining balance and stabilizing gait. Insufficient training of knee extensors leads to muscle atrophy and progressive overall body instability. However, training knee extensors requires specific exercises which are not easily integrated in activities of daily life. For example, even if walking is one of the most popular daily exercise, its training effects are limited to lower leg muscles. To better integrate knee extensor training in daily life we are developing a training device which can apply additional mechanical load on the knee joint during daily normal walking, to extend the training effects of simple walking to knee extensors. We projected a longterm study to develop an integrated system which combines a training function with an assisting function. Integrated sensors measure the biological data of muscular activity to automatically select the proper mode in real-time. In 2019, we designed a prototype of the training device and evaluated its effects on the knee extensor muscle with preliminary experiments. The results validated the feasibility of the training system and showed that the training load need to be adapted to the gait phase during walking. In this study, we improved the training device with active resistance component to adjust the training load in real-time.