While there are individual differences in how fast the neuromuscular system adapts to exercise, the ability to adapt is absolutely required in order to maintain normal function. Significant abnormalities of the neuromuscular system result in disabling conditions such as muscular atrophy or muscular dystrophy.

As far ar I know, Yudkowsky is able-bodied, therefore his muscles must exibit a response to exercise within the normal healthy human range.

The fact that he attempted to train and didn't observe any significant strength increase is best explained by the hypothesis that he used an improper training regime or just didn't keep training for long enough, not by the hypothesis that he has some weird alien biology.