It's not that I couldn't do other workouts during marathon training, it was more about how I prioritized my time and not wanting to jeopardize training with something brand new. Today, I had the chance to try something new.
It's called the Lateral X, and it's an elliptical style workout with more of a side-to-side motion. It was easy to get started and definitely worked my quads, but I had assumed it would give more of a glute workout. The pictures on the machine indicate a few different motions one can do, so maybe I need to do a little research online to see how to optimize it's use for my training.
Looking forward to my next new cross training day!