Gladiator

Early novel by Philip Wylie, noted author and social critic. Inspired much of Superman, but this novel is so much more. Republished many times and still in print, it is also freely available at Project Gutenberg.

Professor Danner is fascinated by animals that can lift multiple times their weight, jump multiple body heights and lengths, etc. He perfects a serum that can achieve that, and the incident with the cat has some humorous bits.

After that, the story changes, with Danner treating his unborn child. The remainder of the novel is about Hugo's upbringing and the challenges with the use (and curse) of his abilities. The most poignant of these is World War I.

Siegel and Shuster used Danner's strength well in the pulps of the day, and picked up on the small town upbringing, good guy life saving, bullet proofing and crime fighting from here. More about Supe's challenges, including sports and wars, could be quite interesting for the franchise. Or maybe they've already been done - I can't keep up with everything in the comic world.

What I can recommend is finding this nearly 100 year old novel and giving it a read.