I was all super-excited to tell you that I finally figured out what Musashi’s strange pose is from, but of course Dogasu’s comparisons has had it for forever-long and I didn’t know…  But I got a lead from a manga I have at home, and I figured it out myself!
Anyway!  I’ll tell you again for fun!  Musashi– and a lot of TR’s nuances this episode– are based off of a 1975 manga called 嗚呼!!花の応援団 (Aa! Hana no Ouendan), or Aa! Flower Pep Squad.  This gag-manga series, from manga-ka Dookuman, is about a rough-and-tumble pep/cheer squad for Minamikawachi University.  The leader Aota Akamichi has a signature pose, which is what Musashi is doing along with the accompanying cheer, “Kuekkueekkue!"  (It’s pretty discomforting, to tell you the truth!)  The ”osu!“ that they do before the big cheer is also in the manga.
I found a song for the series on YouTube, which has on-screen Japanese lyrics.  The manga was made into three live-action films in the late ‘70s, and a remake was made in 1996.
There is your obscure cultural reference for the day!
(Oh, look, Dogasu also has that TR baseball reference.  It is Kyojin no Hoshi.  Kudos to him!)