I recently began an interval training program, using an eliptical trainer. The best ratio I could achieve that was programmable was 120-120, high - low (resistance and incline). I would prefer 90-120, but I would literally have to change the settings with a stopwatch / timer. Not fun.
The reason I decided on embarking on this program was to improve my athletic performance and endurance during sports. I noticed that when I was surfing last weekend, it was a series of heavy paddling, surfing (basically resting while balancing), and paddling back out fairly quickly. The part that tires you out, is obviously not the short burst of paddling to catch the wave, but the paddling back out beyond the break.
To me, interval training seemed a logical choice for my in-between surf session training. I continue to work on upper body strength training / bodybuilding, but wanted to gain some advantages of endurance training without losing weight.
I am more than happy to hear what other people might recommend for my purposes if I am way off track here.