I do a lot of high intensity interval training with a client 3 days per week. Mostly multi-joint combo moves, but there is a lot of lunging, squating, and tabatas, TRX and spin. Her legs are actually bigger after a month by an inch. Can you suggest another way to get the cardio in besides elipticals, crosstrainers, spin. I have been doing all of this.
Circuit training and running should do the trick. Genetics play key role here and it seems that your client’s quads respond ‘very well’ to resistance training. Maybe you could incorporate some sprints as well. Another way to get the cardio in and avoid any serious impact on the quads is to do some swimming.