User blog comment:Nobody700/How is he so strong?/@comment-197.38.158.228-20151120235518/@comment-97.121.182.12-20160103002342

^ because Saitama's training for an out of shape human was far harder than then the training that Goku and Vegeta did (proportionally). Saitama would have been very sore from day one, but he never took a day's break for over 1,000 days. The soreness would have likely stacked from each day.

This is why Saitama's limiter was removed/broken (not to be confused with a single limit that was broken, but rather, all of them as there is nothing left to generate limits)