I actually had a huge battle with my muscle memory a few years ago when I was transitioning from using the Caps Lock key to capitalize my letters as opposed to the Shift key. It was a very bad thing to get caught up in, because it took me quite a large struggle with my muscle memory and learning overall to completely transition from Caps Lock capitalization to Shift key capitalization. On a good day with solid rest when I am well focused I can type 120 WPM now that I am using Shift!
However, when I was using Caps Lock to go ahead and capitalize, since I had to tap it on & off, even though I did it quickly, it would cause lots of cramps. Bad.