The best way to tell if your exercise is by measuring your heart rate and making sure that it is within your aerobic training range. The formula for estimating your maximum heart rate is: Maximum Heart Rate (bpm) = 220 - Age (yrs). I have trained in the range of 65% to 85% of my Maximum Heart Rate.
Walking/Hiking
When I first started getting into shape, walking and hiking was aerobic enough.
Elliptical Trainer
I enjoyed the elliptical trainer because it was more aerobic than walking or hiking and was not going to further injure my left knee which has started to crack due to my knee joint starting to wear out due to the weight I was carrying. At some point, the elliptical trainer was not vigorous enough to keep me in the training range, so I moved on to spinning and rowing.
Spinning
Spinning is a really exciting group or individual aerobic exercise that involves a stationary bike that has a 38 lb. flywheel and a strong frame to enable the rider to stand up and apply hard working pressure on the bike. When coupled with music, spinning can simulate riding a mountain bike doing flats, sprints, hills, jumps... See the spinning web site at http://www.spinning.com
Rowing
I have found that often spin classes are full and it's not possible to get a spin ride. So as an alternative I have used a rowing machine for the same amount of time. It works my upper body and lower body in different ways from spinning. It's a lot of hard work and lacks the music and group workout that spinning gives you.
