A knee assistive device can serve a large number of people to overcome muscle weakness due to aging and perform normal functional activities of the knee joint. The objective of this paper is to study the effectiveness of a knee brace to aid with normal functions and reduce muscle forces at different walking speeds. The study uses two major muscle groups, rectus femoris (RF) and biceps femoris (BF), for the muscle force study. The Electromyography (EMG) signal was recorded at 3 different walking speeds (slow, normal, fast) under both brace-assisted and normal walking conditions. EMG signals were processed and converted into muscle activation signals and finally used for muscle force calculation. The amount of assistance to each muscle group at different walking speeds was derived and analyzed to see the effectiveness of a knee brace. The knee brace was seen to have provided additional support for motion generation. However, the amount of support is found to be speed-dependent and has a different effect on different muscle groups. At slower speed, the BF muscle was seen to work against the brace, while it was not the case for the RF muscle group.