Originally Posted By GaryRidgway⏩
Pretty sure the 10% claim is based off tested vs untested powerlifting results. Basically the records for untested lifters for the same weight class were about 10% higher.

Now that a tested lifter has the highest overall total Mike Isreatel will probably say they actually hinder your performance.
That sounded hard to swallow, so I checked and it looks like it checks out. The untested vs tested powerlifting records are usually within 50-100lbs, surprisingly.

Which, I guess pure raw strength is one thing, but hypertrophy/growth another altogether, would be my pushback or counter. Strength is heavily influenced by size and muscle but there is a lot more going on.

With muscle size, I'd say there all you need to do is look at bodybuilders from the 30s and 40s and compare that to the chit we have now. Night and day on that one, even if you assume the old timers might be a little bigger or leaner if they were around (and natty) now thanks to better knowledge of lifting, nutrition and such.
All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.

- Arthur Schopenhauer