Is this an effective form of cardio?

I just joined a gym and I'm kind of fitness-challenged. Last year I lost 35 pounds just by mostly dieting but I feel like now's the time to start exercising and try to lose these last 20 pounds.

I've been using the treadmill, starting with a 5 minute warmup of walking at about 5km/h. Then I switch on and off, walking at around 6km/h for 3 minutes and jogging at 8.5 for 2 minutes. I can't do any longer than 2 minutes at this point in time. I do these intervals for 35-40 minutes or so, and cool down for another 5 minutes.

How effective is this? It definitely takes a lot of energy and leaves me dripping in sweat.

I'm just really not sure what the best way to go about doing cardio is.

Thanks for any advice!!

sounds like you've got a great start! just keep pushing yourself. i've been working out frequently for about a year and i sure can't run for 2 minutes. good for you.

you should always think of any kind of cardio in 2 minute sessions....so you are out to a great start....going back and forth from walking and running is a great way to strengthen your heart and lungs while also building endurance...keep it up and you'll be amazed at what you can do in a few weeks!!!

You should check out www.c25k.com There is a link to a program called Couch to 5k.  It will give you a training plan to get from out of shape to running for 30 minutes in a row.  

give it a shot.