Ripped may be a variation of of rippled, but there are a number of other synonyms that also suggest something cut, for example from Talk the Talk: The Slang of 65 American Subcultures (Luc Reid - 2011):
buffed, buff, cut, defined, shredded, sliced, sliced and diced
It looks like ripped came from an extension of cut, itself an extension of defined and moulded by way of having all that is extraneous removed, leaving just muscle. Other terms such as chiseled, razor sharp, shredded, sliced and lacerated follow the same pattern.
The Oxford English Dictionary has ripped from 1974 with an origin in bodybuilding. They say it's also used as ripped up.
Ripped up mirrors cut up, that came from cuts, cut, and clear cut, referring to the sharp angular shape of built-up muscles. These uses of cut goes back to at least 1940, all within the bodybuilding community.
Here's an early January 1976 use of two of the terms together (Muscle Builder, Vol 17, Num 1, Page 43, January 1976), and interesting to see cut-up, which shows similarity to the early ripped-up:
John Isaacs, 45 years young, was unbelievable ripped - more cut-up than a Christmas goose - and he gave the youngsters a lesson in muscularity by winning the coveted "Most Muscular Man" award.
And the next paragraph shows cut used as a noun rather than adjective:
Among the also-rans, Dave Mastorakis was massive but lacked the former cuts he displayed last year.
More cut elsewhere:
Paul, the giant 225-pound block of granite from Wales, was sensationally thick and cut to ribbons.
Sharp cuts, posing and symmetry gave him a surprise 2nd in the Tall Class.
Joe Nista, 46, returns from retirement with all his former density and cuts.
If we trace the history of cut, we can see how it was used to describe sharp muscles, and how it spawned other similar adjectives and nouns.
This 1974 description of Mr. Universe winner Louie Ferrigno describes exactly what cut meant (Muscle Builder, Vol 15, Num 3, Page 24, July 1974):
Ferrigno needn't have posed, needn't have twicthed a single muscle fibre, or lifted a toe. Just to see him inert was to believe the unbelievable. The biggest superstar ever, and all of him cut to shreds; lacerated, the skin beaten and hacked away so that only sinews and tendons and veins and striations and unbespeakable musclemusclemuscle remained. . .
The following shows why the adjective cut was used, and how it changed into a noun.
IronMan, Vol 23, No 6, Page 11, September 1964:
Randy [Watson, Jr. Mr. America] has maintained his superb definition or "cuts" as the fellows now prefer to call it.
IronMan, Vol 18, No 2, Page 9, September 1958:
Tom [Sansone, "Mr. America 1958"]'s 14½ inch forearm is cut into planes when flexed, rounded and full when relaxed.
Strength & Health, Page 26, November 1952:
[George] Paine wins "best legs" and it's easy to see why. He has the deepest "cuts" I've ever seen in his thighs. They look like they've been chiseled out of marble.
Strength & Health, Page 23, July 1940:
"Chick" Deutsch, won the Best Abdominals and it was quite an easy victory for him. Seldom have I seen such fine clear cut straight abdominals and external obliques as this young favorite ad popular athlete possesses.