Run if you want to run. If you prefer an evolutionary explanation, remember that wounded game animals by no means just fall dead when hit. A hunter may well have to run after it for miles, before other predators get to it. Even using modern weapons, hunters today often have to follow a blood trail to the wounded or dead animal.

-Steve

No one's talked about differences in muscles yet so I'll start that conversation. We say different people have varying diet needs, so why wouldn't your reaction to endurance exercise depend on your genes as well?

I've always been jealous of the beautiful muscles displayed by sprinters and middle-distance specialists, but when I rode my bike I found that after about 3 hours on the road (in an event) I was steadily passing a bunch of people with beautiful muscles.

My family carries almost pure "slow-twitch" muscles and if a lion chased us we'd be dead. On the other hand, once we're fit enough to go for an hour we can go all day--literally. I think we carry nomadic genes from the high north as our skin is Transylvania-level pale with very dark hair and eyes.

Isn't it possible that some of us--such as the Kenyans mentioned by gydle or Caucasians like me--are adapted for endurance exercise?

Pretty much all research ever has shown the incredible benefits of cardiovascular exercise. Running slow, running fast, they all have their benefits.

Reactive oxygen species are involved in upping the bodies own antioxidant systems, as well as being one of the triggers to adapt. If you supplement vitamins E and C in large doses, you can inhibit the insulin sensitizing effects of training (ROS are GOOD sometimes).

The backlash against lots of low intensity cardio is probably just a current reaction. Before that, there was a backlash against intervals, and before that, a backlash against lots of low intensity. You can read about Evolution of Training.

I suspect a lot of people in the paleo crowd tried the "lots of cardio, low fat" method of losing weight unsuccessfuly, and because of that now dislike cardio and carbs. It's always important to keep in mind context, and low fat/low carb, high intensity cardio/low intensity cardio can all be healthy provided they are programmed intelligently. Do whatever makes you feel good. I know I couldn't get through certain bad weeks in my life without running and weightlifting.

If running makes you feel good, do it. Do it as much as it makes you feel good. You'll probably end up doing a moderate amount of volume across a range of intensities. Long and slow when you feel like it, short and fast when you feel like it. Just build up to your volume slowly and you'll avoid a lot of the issues that plague runners (especially if you do some strength training).

All that being said, if you want to be an elite runner, you have to be willing to put in a huge amount of easy volume, at least for the first 10 years. After that, it might be okay to back off on the base training. Don't believe the hype on crossfit endurance, they haven't created a single elite athlete. Last I checked most elite runners put in about 85% of their miles in at an effort of 1 (on a scale of 1-3).

Perhaps this will interest you

Are we born to run ?

Age-related changes in skeletal muscle reactive oxygen species generation and adaptive responses to reactive oxygen species

Marathons and Heart Damage

I guess it all depends from the context

It looks like sprint is better option when time management is a problem and far more sustainable. You can't deny your own results, so if it makes you feel THAT good, just run.

I love running. I do it because I genuinely enjoy it and not for any weight loss benefits. Yes I do it for the endorphin hit, just as I enjoy lifting very heavy weights for that feel good hormone shot. I run slow though and not hard core tempo running that keeps my heart rate up in the 85% range. Being on my feet hours and hours a day as a nurse exposed to disease, stress, people's problems is probably worse but someone has to do it.

I ran consistently for about 3 years, about 10-12 miles per week. I am definitely not built for long distance running (short arms and legs, "big boned", heavy musculature) but I did really enjoy it for a while, for many of the reasons that you say.

I was however worried about injury. I got a soft tissue injury in my knee a few years ago which sidelined me for about 2 months. I was also a bit frustrated by my lack of weight loss and muscle definition. Despite all of the running, I could not seem to lose weight. Going Paleo and low carb, I lost about 7-8 pounds, but I couldn't lose more, and my legs never really seemed to get stronger.

After reading various things in the Paleo blogosphere about exercise, I made the difficult decision to stop running and switch to high intensity strength based workouts. I had achieved pretty good running distance, and could jump up and run 3-4 miles at the drop of a hat and hardly be tired afterwards, and I did not want to lose that.

But this was the best thing I ever did. After changing workouts, I lost about 7-8 pounds quickly (a few weeks), and the weight and waistline kept coming off, though I made no other dietary changes. My appetite, mood, sleep, etc all got even better than they were before. Something about the strength workouts definitely stimulates some hormones or something that made me feel great even days after working out. I am now getting muscle definition for the first time, and can leap up a flight of stairs 2 or 3 at a time with no problems.

One of the best parts about it though is that these workouts are so much easier on my schedule. I had been running about 45 minutes 3-4 times per week. Now I workout about 20-30 minutes 2-3 times per week, about the half the time overall. When I am super busy, even two 20-minute workouts in a week keeps me on track. It is so much easier to keep this schedule that I feel this is more maintainable.

One thing that has been instrumental for me in figuring out what I do for exercise has been figuring out what I feel good doing (like I've worked hard), and what gives me pain or leaves me feeling wrung out and crappy. I am pretty sure that ancient/paleo people had different people in the tribe who were uniquely suited to different tasks -- as I've said before, I don't have the balance or build to thrive as a hunter... but I'm pretty sure that hunters ran long distances at a stretch -- and sometimes at the drop of a hat -- so I figure that some folks are meant to be runners, and others just aren't. I'm not, but that's OK. There are a lot of other cool things I can do instead. If you enjoy it, and it makes you feel good about what you're doing, then maybe you're just a "runner" type -- so enjoy it, don't obsess about it, and believe your body when it tells you you're doing something good for it.

I by no means think distance running is bad for us. But 40-90 minutes every day, that seems excessive, and excess is bad for us. A weekly mix of resistance training, sprints, sport of choice whether that be flag football, basketball, of going out for a 10 mile run I personally don't think it will hurt. Like I said, moderation.

I wouldn't say it's 'unhealthy and bad for you', but running is taxing for the body (but easily enough made up for with rest and adequate nutrition), and taken to an extreme, there's evidence it can cause permanent damage to your heart. CW seems to regard running as a benefit for your health in every way, and that's definately not the case either.

Evolutionarily speaking: yes, we're very well-equipped to run long distances better than most animals, we're unheard of in this ability among primates, and that's why we can get a 'runner's high'. But in a natural evironment it seems people avoid this kind of extreme energy expenditure. Hunter-gatherers run to hunt large game, or even persistance hunt (though that's usually performed only by a couple expert runners), but not every day, and only a few people in the tribe. Hunter-gatherers are very active but usually at a low level - walking, digging, carrying, grinding, butchering, cooking, making tools (much of that performed seated/squatting). Especially hunter-gatherer women who are often carrying a nursing infant with them all day. I can't help but wonder if that's why exercise-induced amenorrhea is so common even in modern women who eat more calories, more carbs, ahnd have more protective body fat...

Cardio also does not help many people to look good naked. Sometimes I think it actively hurts (check out all the posts by people doing Crossfit 2x or more per week who have gained guts while eating paleo).

I rode a bike like that for years. The low-impact version of running. Didn't hurt me a bit (except for the accident that cost me an achilles - now I'm REALLY restricted to low-impact). But it didn't save me from the disease of SAD-induced obesity and heart failure. Actually, the strengthened heart saved me from dying. But not the disease.

If you enjoy running long, run long. That's different from adding the idea that it's good to run long often, especially on some schedule invoking high degrees of discipline. I loved running marathons and ultra marathons. Then I found it wasn't much fun any more: the "oh it's Saturday, time for my weekly 15-mile trail training run" approach. These days my focus is HIIT which, again, I happen to enjoy. And three weekly gym workouts emphasizing compound movements. I still am drawn to the marathon, as an event; attracted to the distance in some romantic, mythic sense, as opposed to actually wanting to train up again. If I decide to run another marathon, I sure won't use classical high-volume training. I'll do it for fun, forget about speed, and will do my best to mitigate oxidative stress during and after.

I ran the Kauai Marathon last year. Great fun. Best part? Kauai. Repeat: Kauai. My training was "sub-optimal" (in terms of standard marathon training). I had a blast. If you are a marathoner and "had a blast" is part of your regular vocabulary, keep it up. Otherwise: WTF are you doing, dude?

Running is a very healthy aerobic exercise, both physically and mentally. Physically, it leaves your heart in GREAT condition, and most importantly leaves you skinny. You are less likely to obese or overweight. I am a cross country runner as well as a track runner. You don't want to end up overweight now do you? take the right path..... Peace out