I remember reading that, but I can't remember if it was from a canon source, or just a novel or such like. I have half a notion it may have been mentioned somewhere during TOS. Supposedly it was the actual reason behind the Vulcans' elevated physical strength. But then in any episode where Vulcan appears, offworlders used to ostensibly lower gravity (humans for example) seem to move around completely at ease and unencumbered, which should not be the case. I've recently been watching season 4 of Enterprise where Archer goes on a long march through a desert on Vulcan and appears completely not-weighed-down. Reed and Mayweather don't seem unduly gravitated either, when investigating the bombed embassy.