Bikram Yoga is the method of 30 poses and they heat the room to 98 degrees. You can read more about it on the internet.
The reason I think Bikram helped me swim better more than anything else is because it opened up my upper body, my lungs, my reach, extension, flexibility etc ...... I can not tell you how much it rocked my world.
Bikram yoga is tough, I had no idea how tough it was I could not finish my first 5-6 classes I could not even hold my arms up at the the end of the class. I thought i was fit :) but there were people in there who looked not in shape just blowing me away.
Its all about the balance of controlling your strength. Try it but you have to give it 3-4 months. I would incorporate a run before the 90 MINUTE class !!