I read this in the March 07 edition of Women's Health magazine, as if I'm not confused enough about cardio and weight lifting and calories :

"Really long aerobic sessions, say 60-plus minutes, could burn needed muscle (p. 102)."

If you've already covered this topic a zillion times, thanks for responding once more.

I've heard this several times before too .... The studies say that any exercise after 60 minutes has depleted the glycogen stores which is what you'Re burning when doing when exercising... I think, this is the proper explanation, I hope someone comes along and explains it better than I can ... I usually get bored with more than 60 mins of cardio anyways, so I never do more than an hour, except when it comes to biking in the summer....

There's so many if's and's and but's ... I just figure that some awesome consistant exerciser might burn muscle after 60 minutes but probably not a wobbly old novice like me. Who can keep their heart rate in the proper range for over an hour. Not a lot of us amateurs ... me thinks.

In my humble opinon ... it's a detail that most of us need never worry about.

We also discussed before that it was an hour + consecutively. So if you do 2 - 1 hr segments like I did yesterday with a recovery time in between, you'd be fine. I can't imagine anyone doing 75 minutes of cardio at one shot anyway, can you? I just don't have enough spare time to do that. Even a power class wouldn't count bc you are doing other, muscle building things, in between, it's not like all boom-boom cardio for 90 minutes.

Marathon (or half marathon or 10 miler) training. Triathlon/training. Long bike ride. Long swim, probably. And that's not even going into the gym.

I have no cites but the idea that you suddenly turn into a pumpkin after an hour strikes me as hooey. If you can run for two hours (say 12 miles) you are more fit than someone who can only run for 6 miles, not less.

I've heard this many many times before and the reasoning is your body needs fuel for cardio. It has about an hour of stores to handle cardio but after that, it will start burning muscle for fuel.

I've also heard that marathoners have the highest body fat percentage of any athlete, partially due to this effect. Of course when you are comparing athletes, highest body fat percentage is really all relative

Elite marathoners, or weekend athletes? I can't think of a lot of other sports in which you and I compete against professionals. But you and I can both get into the New York (or London or Chicago or Boston) marathon and run in the same event as the best in the world, running the same course at the same time.

Trained distance runners hit "the wall" (no more glycogen to burn so the body burns fat; running becomes a LOT harder) at around 18-20 miles. In other words, they're fueled by burning glycogen for the first 2000 calories/20 miles or so.

I'm googling and googling and getting nowhere wrt burning muscle. There's lots out there wrt running/the wall/glycogen and I see no reason why the same concept wouldn't translate to other endurance activities.

So I am doing harm by 20-30 mins of mixed free weights and calestetics (sp?) and then 30 min interval training then 30 min walking. If I do not do my exercises in the morning they will more than likely NOT get done.

No, you are not doing any harm whatsoever... Exercise at any time of day is better than none at all... Do it at the time that is best for YOU

thank you Ilene