small frame=usage frame=fast frame. (it did used to make me wonder)
some nice explanation on the terminology from the Liang De Hua performance youtube page (chose his students, for some reason i prefer it..)
this is the Yang small frame, or Xiao Jia taught by Yang Shaohou to Gu Lisheng, also called Yong Jia or usage frame. In 1947 Gu Lisheng was in Gui Yang, there was a martial arts competition event by The Central Guoshu Institute of Gui Yang, and Gu Lisheng was a judge at the exhibition. He demonstrated this small frame in the event and received great praise.
I learned this set from my teacher Chi Qingsheng, the last indoor disciple of Gu Lisheng.
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However, a small frame doesn't mean a small movement frame.
For example, master Ma Changxun also stated about the small frame as follow:
Wu family skill came from the Yang family. Quanyou learned it from Yang Luchan. When I (Ma Chang Xun) was following master Liu (Liu Wancang) learning boxing, the name "Wu style Taijiquan" didn't exist. It was called either "Yang style small frame," or "small frame." You could say that it is one part of the Yang family.
"Small frame" (Xiao Jia), can be easily misunderstood because the small frame movement doesn't look "small" at all. The relationship between the "Small frame" and "Big frame" are not related to the size of the boxing frame but instead, relate to other stories. For example, the first set is called "big frame" and the second set is called "small frame." The meaning of those names refers to a big brother (1st set) and a little /small brother (2nd set). It does not mean that Wu style boxing is small and Yang style is wide and open. Wu style Taiji is also very wide and open. You can see that master Wu Jianquan, Master Wang Ziying (Wang Maozai's son) and Master Liu Wancang also practiced big movements.
-GM Ma Changxun-
Both of these are attributed to coming from YSH
Gu Lisheng version
Wu Tu Nan version