This morning I had limited time at the gym so I got on the evil arc trainer and had a helluva workout. I literally didn't know if I could finish 30 minutes. I usually do 40 or 45 on the treadmill on an incline or on the elliptical with moderate resistance, and I think I'm getting a decent workout doing that. However, I think my 30 minutes on the arc trainer working hard was actually a better workout. I honestly don't know if I could work out that hard every day at my current fitness level (which has gotten remarkably better but still isn't great).

What do you guys do? Harder, shorter workouts or longer, moderate workouts? What do you think are better, and when have you gotten your best results?

Variety is what gives you the best results. You can only go so hard so often. If you want to get in a decent burn several days a week you need some of those days to be at a lower intensity.

Work the entire aerobic spectrum, not one segment of it.

In terms of cardio, I tend to do both. I mean, I love the intensity in a good spin class, but I can't go to one every day (I could, but I'd probably have to give up things like, oh I don't know, using me legs for any other purpose ). Sometimes I like a nice long, easy run. Sometimes I only have 1/2 hour and blast it out with intervals on the treadmil. It really depends.

Although, I usually want to get the most out of my time, so I'd probably vote for the shorter, more intense workout over the longer, easier one. However, intervals are a great way to get the best of both worlds. Ramp up the intensity (or incline, or resistance, etc.- you can do this on any cardio machine) for a few minutes, then back off and recover for a few minutes. Burns tons of calories in a shorter amount of time than the slow-and-steady approach and is also training your body in a different way. Intervals are part of my cardio usually 3 days a week.

I do longer, moderate workouts but mainly because my workout consists of me walking on the treadmill at 3.0 (4 elevation) while working or browsing on my computer (I'm on the treadmill as I type this). My husband rigged up a homemade tread-desk for me (google it), and it's my main form of exercise. I find that I'm so efficient in every aspect of life that I find it difficult to devote specific time JUST for exercise; each time I've tried that, I don't stick with it more than a year. This tread-desk thing has worked out well for me because I'm exercising while getting work done.

Beyond that, though, at my age (43), I don't want to risk injury by going "balls out" in my workouts. When I've tried that, I regret it. For example, I visited my sister in August & went with her to the gym. I ran at 6.0 for 10 minutes and walked at a fast speed for another 30 minutes or so. Because I'm not used to jogging, that 10 minutes was difficult for me. The next day, my knees bothered me, and they kept bothering me for at least two weeks more. I don't remember that happening in my 20s or 30s even at a heavier weight.

Nevertheless, I do think mixing it up is a good idea.