TweetMan I do it all but the elliptical is my go to. I set it at medium and warm up for 10 minutes. then I bump resistance to almost max (still working on getting there) and do a 85-90% sprint for one minute. Drop resistance and coast at an easy speed for one minute. Do this 4-5 times to start and work up to 10-15 times. You will be huffing and puffing and your knees will feel fine. Watch your heart rate. I have gotten it well past my old man max before.

I like to also do tabata on the bike. 20 seconds on 100% sprint, 10 seconds off. at 5-6 you will be out of air then I go at a normal pace until i get my wind back and my heart rate comes down and do it again. Best way to increase VO2 max.

And I like the tread climber as well. I normally do it at max speed for 5 minutes. That is a fast ass pace man. I try to push off each time with my calves. they will have a brutal pump and burn when done. Also DON'T be one of those people that hang off the machine to take pressure off their steps. Like folk who do the treadmill at max incline then grab the bars and lean back. Dammit I want to slap em. If you want a back workout then go do back!

As I have gotten older cardio is more important to me for long term health.