The training borrowed from 36th Chamber of Shaolin?
I love the Karate Kid, it's probably my favorite movie of all time. I've always thought the training was actually believable, if a bit rushed.
If you look at The 36th Chamber of Shaolin, you have the same concept, with the difference of the training taking place over a few years time. In 36th Chamber, each 'chamber' is actually a school with some weird exercise or task to perform, that doesn't immediately translate to fighting power/skill on the surface.
But, over the course of completing these tasks, such as carrying buckets of water, or gonging a bell with a pole, the trainees slowly build their bodies and also learn kung fu techniques. I don't know, just thought it was an interesting comparison, and I wonder if it influenced the writers of Karate Kid at all. I don't think it's so cut and dry, because while 36th Chamber is widely known today thanks to Wu-tang Clan music, I'm not sure how well known that film was back in 1983/84.