It’s quite common for many students once they have passed a grade, to never really feel the need to continue their study of the Heian Kata.
It’s quite common for black belts to have completely forgotten their previous kata, being so caught up studying Bassai, Empi, Jion and Hangetsu.
However, continued attention and study of these Heian Kata should follow, and not just up to Black belt. Many very senior Dan grades devote most of the kata training time to the Heian kata’s, for these kata teach such important fundamentals, and need to be perfected for a lifetime.
Heian Yondan, the fourth in the series is a very popular kata. More than any of the earlier Heian Kata, Yondan introduces a new type of rhythm to kata training. It has interesting contrasts between very deep and slow to incredibly sharp movements. This contrast between slow and fast introduces rhythm to the beginning student, and helps them to develop the control to not just rush through the kata. It helps them develop their leg movements, and the ability to synchronize leg and arm movements.
This kata introduces juiji-uke, Shuto-uchi, kakewake-uke, and hiza-geri, and perfection of these new movements is imperative in your continued study of the rest of the Heian series.