I want to know how to improve my push off in Kendo. I mean the impulse of the fumikomi.
Answer: To increase the power/impulse of fumikomi, you need to work on not only the kick of your left foot but also the pulling-up motion by your right foot.
Many people tend to use the right foot only to make a huge bang noise. But the right foot is very important to increase the force created by the kick of the left foot. There are a few articles dedicated to fumikomi: