I attribute my success to a couple pointers I'd picked up researching the cramping-while-swimming problem:
- Good kick form: when switching to the breast-stroke kick mid-workout, I've concentrated on my form. Unlike before, I've kept my foot locked in place throughout the entire kick stroke. Previously, I'd relaxed the ankle, and I think that was contributing to muscle fatigue.
- Biting my upper lip: Really, it works! (for me) This past workout, I could feel one of my toes starting to cramp up, so I bit my upper lip as best I could for the next length of the pool (kinda hard to do that and breathe appropriately) and it worked! I don't know how or why, it just did. Yes, I must've looked like a piranha, but I was a cramp-free piranha.
Oh, and I also learned not to try to bite my upper lip while doing the breaststroke: it simply opens up the nasal passages for a good flushing of the sinuses. You're welcome!