When we talk about "chronic cardio" we're not referring to some obscure Dr. Dre exercise video.

Um, we already get this. Read Mark Sisson for gosh sakes! To paraphrase:

Move slowly (walk/hike) quite a bit.
Sprint once in a while. Lift heavy things once in a while.

High intensity stuff should be pretty brief. Low intensity - do quite a bit.

I haven't seen a single person here recommending marathons or ultramarathons as healthy. Otoh, if that's your thing, more power to you - just be aware of the downside. I'm pretty sure most of us here are.

This NYT article reviews some recent research on the effects of high volume running on scar tissue in the heart. It focuses on long-term, always active, non-smoking runners. There is scarring in heart tissues among most if not all of them. Even rats who are made to marathon-like running and high volume training, show scarring of the heart. Scared heart muscle is more likely to go into fibrillation because the contraction pulses across the heart become more fragile and lose their coordination. A scarred muscle does not have the flexibility and contraction force, so the coordination breaks down at mutiple sites. The good news is that this is reversed, in the rats, when they are no longer made to run excessively.

I have argued that metronomic training reduces the chaos in the heart. Scarring of heart muscle is an obvious way that would occur. A scarred heart cannot have the power law variation of heart beat intervals and is more likely to lock onto periodic contraction patterns---fibrillation.

This only looked at heart muscle. Other tissues of the heart may also be damaged, particularly the valves. There is often damage in other tissues as well, ankles, knees, hips, the foot, the upper respiratory system, the kidney (which has to clear the damaged proteins), and other organs that may be but in transitory state of ischemia.

We are not against running: easy forest running with cuts and variation of pace, or sprinting a variety of distances at varying pace, if fun and easy. It is the metronomic, forced pacing and long duration of long-distance running that is unnatural. And piling up the miles is not enjoying much of anything.

I've been listening to this guy a bit lately. He is pretty vehement about limiting aerobic activity - http://www.naturalhealthpodcasts.com/PodCasts/heart_attack.mp3

He has a lot to say about fibrosis in general as well.

20 minutes of lifting heavy things once a week, 4 minutes of sprints once a week. I think I'll survive.

I tend to just listen to my body..sometimes it wants to do two hours a day of sprints,rowing machine,elliptical,and a beach hike.Sometimes,like today,it's going to tell me" &*( you, buddy.we've done enough right now.Take a nap."

You can't feel guilty when you take a rest day or two. Listen to your body and train hard on the days you feel your best.

One thing not brought up in the usual criticisms of chronic cardio is that most of the research was conducted under the assumption that a low fat, high carbohydrate diet is the healthiest, so that's what the subjects were eating (carb loading, trying to be vegetarian, etc.) Over the years, you can get depleted on this type of diet whether you're running marathons or not. I'd be interested in seeing a study done of paleo dieters engaging in steady state, high intensity cardio and whether the same damage occurs.

so if I plan on running multiple marathons a year I need to worry?

I think I was overtraining previously, and have changed my workout schedule a bit in order to address the issue.

New schedule:

Sun - Tabata sprints (10x 20 sec. all-out sprints w/10 sec. rests between each)

Mon, Wed, Fri - Stronglifts 5x5 program

Tue, Thu - morning calisthenics, regular walking during the day

Sat - big hike with the dog, usually some tree-climbing and driftwood-balance-beaming is involved

I am also starting an IF regimen next week with a 16 hour fast followed by an 8 hour feeding window. We'll see what happens :)

A friend of mine asked me recently to do a marathon with her. I haven't figured out how to say, "I don't believe in marathon running." So, I just told her I hate to run. That is the truth.

Mark Sissons lays out some guidelines, but to be honest, the training WOW programmes he recommends I'd say aren't tough enough if you are really want to get competitive in any sport - I think both Sissons and de Vany got ripped and now just do the minimum to maintain that level.

In the article it doesn't really specify what how much these people were training also - like Lacey says diet has a role too.

Personally I don't think running marathons is healthy, I have no plans to ever run one.