I heard it more than once from many people and some teachers as well.
Gym + Dancing = Bad idea cause you might lose flexibility and the ability to use muscles isolatedly.

Though Im curious. If leg , abdomen and lower back muscles serve as the means to make , control and time movement and of course to balance us , would a gym program specifically designed to train those muscles exclusively prove fruitful or would it still be hindrance ?

I'd be interested in hearing information on this also. I can't say I've ever heard of a gym workout hindering your dancing.

Certainly a standard gym workout doesn't challenge you to use your body in the same way, but how can and improving overall strength and endurance be a bad thing?

Personally I prefer pilates/yoga/dance based fitness programs, but still do the more traditional workouts for variety as well.

"but how can and improving overall strength and endurance be a bad thing?"

It can reduce flexibility if taken too far.

Do you mean if I were to try and bulk up? I have heard that excessively large muscles can actually reduce flexibility. But that usually applied more to men/women whose goals are muscular size/body building. How many of us actually go that far, as dancers? I've also read that flexibility without proper strength is harmful as it leads to greater injuries.

It isn't just a question of flexibility. If you bulk up too much it can destroy your endurance.

All those muscles suck up blood, lots and lots of highly oxygenated blood. If you bulk up too much you aren't going to have the stamina to make it through a full dance set.

ALSO...those big heavy muscles can be too much to actually hold up. You would think with the reps and the weights it wouldn't work that way, but you have to realize biceps and triceps, etc. can weigh a ridiculous amount.

If any of you are boxing fans, you will instantly understand what I mean. The guys who get too muscular are in greater danger of punching themselves out because their arms are heavy, and it takes too much energy to swing them and control them. Its counterintuitive but its true, and its the same in dancing. Think of how much of the time you have those muscles engaged and moving, at or close to shoulder height.

In terms of legs, be careful there too, because if you bulk those muscle up too much you won't be able to achieve proper leg positions which can be very important. Think about how much flexibility you have to have in your hips, thighs, knees, calves and ankles to do even simple latin steps.

A little pilates? Yoga or aerobics maybe, but hardcore shaping? Trust me, I have a bunch of muscle heads in my life and it isn't going to help you dance.