I seem to have an issue (maybe due to how I lift, but maybe genetics) with my arms specifically not looking hard, except when holding a heavy weight or lifting a heavy weight. I am not sure what this is due to, but it's annoying. My muscles look hard and full as hell when I, for example, lift the 90 lb dumbbells off of the rack and then sling them up to shoulder-height to begin military presses, but when I am not holding the DBs, my arms look "flat."
I also follow a pretty low-carb diet, never getting near 250 grams a day. I'm at most around 150, and more normally around 100 grams, sometimes being as low as 30.
What would people recommend (supplement, dietary, or training advice) to get more of a "hard" and "strained" look to the muscles, while they are at rest?