How many hours of "cardio" is it safe to do in a day? Is it ok to do 60 mins of cardio in the morning and then 60 mins at night?

(Stair climber, elliptical, treadmill) etc

Go by how you feel. Are you feeling energized or depleted? Strong or weak? Healthy or injured ?

I have plenty of days where I do 2 hours of cardio (or 11 if I'm hiking.) I usually feel better on those days than the days I do zero.

Our bodies were made to move.

When I played rugby I did about 4. I was 20 years old and did a cardio warm up on the stairmaster, went to practice for 2+ hours and THEN did an aerobics class. I was the thinnest/most muscular I have ever been.

A few of words of caution, from someone who has been there, done that.

First, there are diminishing returns. Aerobic exercise -- particularly long sessions with moderate intensity -- will burn muscle as well as fat. If you're not lifting and eating sufficient protein to maintain muscle mass, you'll end up smaller but flabbier.

Second, if you don't give your body time to rest and heal, you put yourself at risk for an overuse injury (e.g., tendonitis, bursitis). This will put you out of commission and stall your progress. Not saying everyone will get an overuse injury from two-a-day cardio workouts: it depends on your starting point (more in-shape people can manage more stress on their bodies), age, diet, and just plain old genetic factors.

Third, mental fatigue. Any program gets boring, but two-a-day cardio sessions in a gym are a recipe for mental burnout. You may last a day, a week, a month, or maybe a year (probably not that long, but it fits the tune of "friends" better). But, you're in this for the long haul, no?

If you have a base of conditioning already, try mixing HIIT (high intensity interval training) into your cardio routine. 12 minutes of HIIT can do more for conditioning and fat loss than 90 minutes of slogging on the elliptical.

b. strong,
Kim

^^^^ THIS all the way!!! I couldn't have said it better myself Kaw!

My motto is: "It's not how long you can exercise, it's how many days you can exercise". Burnout's a MAJOR problem when you start with too much too soon. I'd recommend cutting down the time (as Kaw suggests) and upping the intensity...perhaps add 15 min...of weight training to start. You'll see greater gains (muscle) and losses (fat).

Kaw - I just recently found my exercise logs from a little over a year ago....I was 14.2% bf at 148 lbs..grrrrrrrhhh! But I looked as you do in your profile pic...super lean...boy I miss that! Here's to another crack at it.

I agree with Kaw!

Additionally, I have set up what I refer to as my "baseline". I'm all about pushing myself to the max, but there does always come a day where I just can't do it anymore. That's when I revert back to baseline. For me that's Spin class M/W/F, lifting T/Th. Additionally I throw anything on top of that I want to. Right now I am additionally doing an extra 1.5 hours of cardio M-F. But that is ultimately unsustainable. I'm just having fun with it.

Ditto Kaw. And for what it's worth the other issue is that if you're exercising this much to lose weight you'll likely do it to maintain weight as well. So if you were to get injured and not be able to exercise as much and not adjust your calories as necessary you'll start to gain the weight back. I have this concern for myself. I run 20-25 miles a week, which isn't crazy, but it allows me to eat quite a bit more and maintain my weight. I have to be very aware of this in case I get injured or otherwise can't run as much. I will need to take my calories down significantly or find another method of exercise.

Thanks to everyone for the very helpful answers. So far, everytime I go to the gym whatever machine I am on I always do really hard intensity for what that's worth. I am not sure if that's good or bad. But if I am on the treadmill I'll be walking at almost 15 incline. Usually some body part is burning afterward. So I hope I am building muscle, too. But I try to work a different body part every time I go.
I think instead of doing a machine 2x in a day I will just do a brisk walk in the evenings with my daughter in the stroller.
I just feel so so so much better when I am active. I would rather be out hiking/jogging/walking then sitting on my computer LOL