What was reported
In 1973 Arthur Jones ran a short demonstration at Colorado State University with bodybuilder Casey Viator, using brief, infrequent Nautilus sessions to one set to failure. The reported result — roughly 63 lb of bodyweight gained in 28 days — became the headline figure for HIT.
Why it is debated
The study had no control group, a sample of essentially two people, and a central caveat: Viator was regaining muscle he had lost to illness and a sharp weight drop, which makes rapid regain far easier than building new tissue. Jones designed and reported it himself. Those are reasons to be sceptical of the number, not to trust it.
What HIT takes from it
The honest lesson is narrow: brief, hard, infrequent training can produce visible change, and the case does not depend on one contested demonstration. The proof that matters is the evidence in your own logbook, run through the method over time.