Another Superpower that Time Forgot?

Mark Engblom had a lot of fun with these a few years back but here's one he missed.  Apparently Superman can shrink or expand his muscles at will:

In the story, Superman is supposedly out of town and so Lois hits on the bright idea of having Clark dress up in a suit to foil some gangsters.   Incidentally, it is often mentioned that DC took Siegel & Shuster off the comics when they filed their copyright claim in 1947; this (April 1948) issue appears to be the first without their credits on the title page, and the artwork is definitely sub-standard.