I'll start off with an anecdote. It's said that Miyagi was originally going to call his style, "
half hard" until someone pointed out it could be taken as a male sexual condition

. And so we have "goju,"
hard-soft. I'd guess there's a 50% chance of the story being true.
Uechi spent around 15 years in China learning MA (Miyagi's teacher, Higashionna spent a few years there as well studying at the kojo dojo and with Arigake Seisho). I don't know the exact nature of Uechi's training there. But when he came back to Okinawa his personal style was
pangai-no'on. His son renamed the style after his father to honor him (and perhaps to "Okinawanize" the name as well).
Uechi-ryu retained a little more Chinese flavor than goju did. Aside from the iron shirt aspect
hoshin1600 discussed, sanchin is a kata that teaches "rooting" oneself to the ground. Miyagi added the clenched fist and tension
during the hand techniques, not just at the end. This develops the ability to transmit horizontal power towards the opponent while keeping one's body vertically rooted to the ground, regardless of the resistance met by the strike. This is a simple explanation that does not do justice to the concept. I believe this is a main element of sanchin as taught in goju and isshinryu (whose founder was taught sanchin by Miyagi)
This is contrary to the principle of sanchin as I was taught which is there should be NO change in tension
throughout the kata making it very exhausing and potentially dangerous to do full power (I strained my guts as a young man from using too much internal tension). A major concept is to
remain unaffected by exterior forces. In goju I believe, sanchin is taught to lower belts. My style saves it till training for black. In any event, sanchin is a unique kata with much depth; easy to get the basic moves down but taking years to realize its full potential.
.