...

these are some different kinds of cardio exercises i've tried and what i think about them. the calories have been calculated for 130lb woman's moderately intense workout. if you want more specific calorie information go to caloriesperhour.com - you can find almost any activity's calories-burned value for your gender, age and body size.
walking is one of the best ways to get exercise if you hate working out or if you're not in great shape yet. it's pleasantly unexhausting, but still achieves the goals you want from a workout. walking will burn about 30 calories per 10 minutes.
running is probably the best difficult cardio exercise, in my opinion. aside from the possible joint problems from long-term running, it does amazing things to your body. i find it to be enjoyable because it's not monotonous (unless you're on a treadmill) and works a ton of different muscles in your body. you might not realize it when you're running, but your back and stomach muscles are getting worked really hard as well as your legs. i always notice that my abs are tighter, flatter or sore the day after a long run (especially if i haven't run in a long time). running (6mph ~ 10min mile) will burn about 100 calories per 10 minutes. i highly recommend warming up and cooling down with stretching and walking with a run, or alternating between walking and running throughout your workout.
cycling i started riding the stationary bike because it was the only machine i have at home and i wasn't partial to running miles through negative-degree weather... it isn't the greatest, it focuses mostly on your quads, but you can do other things to assist a full-body workout. i change the position of my legs or back to work different muscles. leaning forwards or backwards will work abs or back muscles, and i lift weights with my arms or move around while in any position. cycling outside is a really good leg workout, especially in a hilly area. cycling will burn about 80 per 10 minutes.
the elliptical trainer is a really good machine because it reaps the benefits of running without stress on your joints. they're also adjustable to create a variety of interesting and beneficial workouts. calories burned vary depending on specific machine settings, but can usually be calculated by the machine itself.
rowing on the erg (ergometer, aka rowing machine) or on a crew team is one of the most complete, challenging cardio workouts. your leg, back and arm muscles all work really hard if you're doing it right. don't bother using the erg without knowing the correct technique or reading instructions, it really isn't a good workout unless you do it right. rowing will burn about 70 per 10 minutes.
swimming is my new exercise of choice. paying for pool membership sucks, but i have to say it's worth it if you're not totally broke (eh-hem.). i thought it would be easy when i first started, until i swam from one end of the pool to the other. i was winded. i spent the first day swimming from one end to the other (freestyle) and spending a minute or two at each end catching my breath. but within two weeks i was going back and forth five times before i had to take a break. swimming is so difficult because you're actually forced to hold yourself up in the water as well as move forward. and if you don't you'll choke and drown. swimming is unique because it works all of the body's muscles, which was quickly visible, yet i never felt my muscles burning (until the next day, like yoga). like running, it will work muscles you don't realize are working, but in contrast it won't put stress on joints. so many people are worried about swimming because of the bathing suit factor...i was at first until i saw all the different bodies at the pool, all wearing whateverthefuck they needed to get the job done. large women and men of all ages not only wore fitted bathing suits to do laps but changed in the open locker-room air (well, i only witnessed the women's locker room). everyone just seemed to do their own thing, and let everyone else do the same. 45 minutes of laps five days a week rocked my body and soul. o pool how i love thee.