So i found these lines in the raws which pretty much is the gist of the whole 391 chapter and SUPER IMPORTANT.
It says, "誰かの結果- Someone's result/outcome" is "someone else's process- 誰かの過程に"
Result being Atsumu and Process being Kita & Osamu.

I believe here's where the "memories" part comes in. Memories become the process for result. Result being muscles. In the sport you just don't have a single memory because it is an collective action of everyone's effort, yours and your teammates.

The effort put in to build thaf muscle. This is the same with rice. The effort one puts in results in an entire field of crop to feed many people.

Yes, Atsumu is someone who does and improves on things on his own but it's mostly cause he has had always someone on his side, his twin, Osamu.
He still is there to guide him and so is Kita - both become the process which results in his growth

His growth is not only the New Hybrid Serve but also, his understanding of the past of what he already did - his Dual serves, not to forget them just cause they are past (we don't need the memories) but to make them muscles instead signifying present.

Ok so I am not really good with translations but if you do have another meaning of the same please do share.
Please *don't attack* me for the translation and for this thread as well it's my first one and just my understanding >_<