She'll increase cardio while still doing strength training. There are plenty of athletes in MMA who are both strong and have great cardio.
Yeah, I don't get that. I'm by no means a fitness guru, but cardio and muscle power by no means seem like a inverse relationship. It's only by ignoring one and training the other exclusively that you'd lose the one in the first place, right? (well, excluding minor gains, for example, muscle mass slightly decreasing cardio because, hey, you've got more mass to carry around if you haven't trained at that mass)
Having an advantage doesn't mean you can't lose. And an advantage doesn't have to be massive for whatever is giving the advantage to be banned. Obviously in Fox's case it's not as simple as when we're talking about Substances or Attire but Fox doesn't need to be lifting women over her head with one hand for her to have an advantage that is unfair for the other women in the division.
I'm not an expert by any means, but it seems like you should be able to divide these fights up into regions, such as:
1) Strength - Pure muscle strength, ability to exert force with your body
2) Energy - How long you can exert your strength, and how long you can keep yourself moving in a high energy situation
3) Determination - How much you really, really don't want to lose
4) Talent - Hey, there's some natural talent involved in all things
5) Skill - Training, training, training. And some more training. Just plain being familiar with your moves, how to execute them, and how to block your opponent's moves.
So there's probably a standard deviation that these athletes have within these regions.
What people are arguing is that Fox (I think that's her name? I'm pretty drunk right now, and sort of doing this on the fly) had an unfair advantage (i.e. her advantage was over the 'standard deviation' (I'm a programmer, I'm allowed to do mathy references)) compared to the other athletes in her league.
Just because her talent, skill, and determination may be on the low end, doesn't mean that she doesn't have an unfair advantage in one attribute.
And that's not even talking about the body development, etc, of being male for 30 years would do for you. I haven't done any research on that, and as far as I know, there's really not much to be bad in terms of such athletic competition.