This content is part of an article series.
There’s no question that regular exercise is essential to health. Our paleolithic ancestors had a different word for exercise: life. For the vast majority of our evolutionary history, humans had to exert ourselves – often quite strenuously – to get food. We naturally spent a lot of time outdoors in the sun, walking, hunting, gathering, and performing various other physically-oriented tasks. We had no concept of this as “exercise” or “working out”. It was just life.
Things are different today. 60% of American adults are not regularly active, and 25% are complete couch potatoes – they get no exercise at all, other than walking back and forth between the car, the cubicle and the refrigerator. This lack of physical activity has profound consequences.
This explains why those who are completely sedentary have between 1.5 and 2.5 times the risk of developing heart disease and a higher risk for virtually all modern, degenerative disease.
On the other hand, we’ve got the exercise fanatics. Many Americans have been caught up in the fitness craze over the last 40 years, devoting countless hours to jogging, the Stairmaster or the treadmill in the hopes of slimming down, getting healthy and preventing disease. But while this type of activity may help with stress management, research suggests that it’s useless for weight loss and may in fact be detrimental to health.
If you doubt this, you’ll have to explain why Americans have continually gained weight over the last 40 years, in spite of increased leisure time exercise and increased energy expenditure.
Why “cardio” doesn’t work for weight loss
When I say “cardio”, I’m referring to steady-state, repetitive activity done at a moderate intensity like jogging outdoors, running on a treadmill or climbing the Stairmaster. [Side note: the idea that you have to perform this type of activity to benefit your heart and vascular system is false. Anything that places a demand on the muscles – including so-called anaerobic activities like weightlifting – will also condition the heart and vascular system.]
Most people are surprised to learn that cardio doesn’t work for weight loss. How could this be? There are three main reasons:
- caloric burn during exercise is generally small;
- people who exercise more also tend to eat more (which negates the weight regulating effect of exercise); and,
- increasing specific periods of exercise may cause people to become more sedentary otherwise.
In an example of the first reason, a study following women over a one-year period found that in order to lose one kilogram (2.2 pounds) of fat, they had to exercise for an average of 77 hours. That’s a lot of time on the treadmill just to lose 2 pounds!
In an example of the second reason, a study found that people who exercise tend to eat more afterwards, and that they tend to crave high-calorie foods. The title of this study says it all: “Acute compensatory eating following exercise is associated with implicit hedonic wanting for food.” I love it when researchers have a sense of humor.
In an example of the third reason, one study assigned 34 overweight and obese women to an exercise program for 8 weeks. Fat loss at the end of the study was an average of 0.0kg. Not very impressive. But the researchers noticed that some women did lose weight, while others actually gained. What was the difference? In the women that didn’t lose weight, the increase in specific periods of exercise corresponded with a decrease in overall energy expenditure. Translation: they were more likely to be couch potatoes when they weren’t exercising, which negated the calorie-burning effect of their workouts.
If you’re still not convinced, the Cochrane group did a review of 43 individual studies on exercise for weight loss. Study length ranged from 3 to 12 months, and exercise sessions lasted on average 45 minutes with a frequency of 3-5 times per week. The results? On average, the additional weight loss from exercise averaged about 1 kg (2.2 pounds). Meh. Assuming they worked out for 45 minutes 4x/wk over 6 months, that means they had to exercise 69 hours to lose that 1 kg.
Why cardio may be harmful
Too much cardio exercise has a number of harmful effects on the body:
- increases oxidative damage
- increases inflammation (the root of all disease)
- depresses the immune system
- decreases fat metabolism
- disrupts cortisol levels
- causes neurodegeneration
Overtraining is especially damaging because of its effects on cortisol. We discussed cortisol at length in Step 6: Manage Your Stress, but in this context what’s important to understand is that too much exercise can disrupt our natural cortisol rhythm and drive levels too high initially, and depress them over time. Cortisol dysregulation promotes abdominal fat gain and muscle loss, which in turn causes further weight gain.
There’s also some evidence that frequent endurance exercise may promote – rather than prevent – heart disease. Dr. Kurt Harris summarized a study performed on 102 active marathon runners and 102 age-matched controls to determine the effect of aerobic exercise on cardiovascular health.
The marathoners were between 50 and 72 years of age, and they ran an average of 35 miles per week. They had no known history of heart disease or diabetes. The control group was similarly aged and also had no history of cardiovascular or metabolic disease.
You might be surprised to learn that the marathon runners were three times more likely to have heart damage than the non-runners. Among the runners, there were 12 heart attacks vs. 4 attacks in the non-runners.
In another study by the same authors, the more marathoners ran, the higher their likelihood of heart disease. In fact, the number of marathons ran was an independent predictor of the likelihood of irreversible damage to the heart tissue.
No cardio? Then what should we do instead?
They performed low-intensity movements like walking, gathering foods or working in other capacities on a regular basis. These periods of low-intensity activity were punctuated by brief periods of much higher-intensity activity – such as going on a hunt, running for a predator or fighting for survival.
This is the type of movement our bodies are adapted for, and thus this is what we should aim for in our daily lives. But how do we do that? As Mark Sisson suggests, we should:
- Move frequently at a slow pace
- Lift heavy things and sprint occasionally
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Move frequently at a slow pace
Moving frequently at a slow pace means approximately 3-5 hours a week of low level activity like walking, cycling, gardening, hiking, performing manual labor, etc. This mimics our ancestral pattern of movement, helps maintain a healthy weight, promotes proper metabolic function and provides a foundation for more strenuous activity. Another benefit of this type of activity is that it’s often performed outdoors.
I think one of the best ways to do this type of movement is to integrate it into your daily life. This could include commuting to work and doing errands on foot or by bicycle, taking the stairs instead of the elevator, doing your own gardening and yard work, etc.
Lift heavy things and sprint occasionally
In contrast to cardio, this type of exercise involves performing movements at very high intensity for short periods of time – usually between 30 seconds and 2 minutes. This is sometimes referred to as high intensity interval training (HIIT).
Several studies have been done comparing HIIT to low-intensity, steady-state (“chronic cardio”, as Mark Sisson calls it) exercise, and HIIT has been shown to be superior in nearly every meaningful marker.
In this study, one group was assigned to “chronic cardio”, while the other was assigned to intervals of 8-second sprints. After 15 weeks, the researchers concluded:
Both exercise groups demonstrated a significant improvement (P less than 0.05) in cardiovascular fitness. However, only the HIIE group had a significant reduction in total body mass (TBM), fat mass (FM), trunk fat and fasting plasma insulin levels.
A pair of studies done at McMaster University found that “6-minutes of pure, hard exercise once a week could be just as effective as an hour of daily moderate activity“, according to the June 6, 2005 CNN article reporting on the study.
The study itself was published in the Journal of Applied Physiology, and it revealed that HIIT resulted in unique changes in skeletal muscle and endurance capacity that were previously believed to require hours of exercise each week.
A follow-up study confirmed the results. Despite the fact that the more conventional endurance exercise group spent 97.5 percent more time engaged in exercise, both groups of subjects improved to the same degree. The group that exercised 97.5 percent more received no additional benefit whatsoever from doing so. Considering the wear-and-tear and increased risk of injury associated with that much more exercise, there’s absolutely no point to doing “chronic cardio” when you can receive the same benefits with a fraction of the time and risk by doing HIIT.
The Cochrane study I linked to earlier in the article also found that high-intensity exercise was superior to “chronic cardio”. In particular, the researchers found that high-intensity exercise led to a greater decrease in fasting blood glucose levels than low-intensity exercise.
Why high-intensity exercise is better
In his excellent book on high-intensity strength training, Body By Science, Dr. Doug McGuff explains that high-intensity training is superior to chronic cardio because it produces a greater stimulus and thus more effectively empties the muscles and liver of glucose. This stimulus can last several days with HIIT, as opposed to just a few hours with low-intensity training.
High-intensity strength training: best of all?
Both high-intensity running or bicycling sprints and high-intensity strength training are effective. But I believe high-intensity strength training is probably a better choice for most, simply because the wear-and-tear and risk of injury is lower – especially if the strength-training is performed using weight machines as described in Body By Science.
This is, in fact, the method of training I’ve been doing since April of last year. I admit I was somewhat skeptical about it all before I read Body By Science. But the research and the physiology was convincing, so I decided to give it a try.
The results have been incredible. My workout varies in length between 5 and 9 minutes a week. That’s right, I said minutes. With only a few exceptions, I’ve increased the amount of weight I can lift, the time I can lift it, or both, with each successive workout. My strength has increased and my physique is, if anything, better than it was when I was lifting 3x/week for much longer periods.
Where to learn more about HIIT
There are many books on the subject, but these are the two I’d recommend for most people:
- Body By Science, by Doug McGuff. The “bible” on high-intensity strength training. Goes into great detail on the physiological mechanisms and benefits behind this type of exercise, and explains how to put together a routine. Doug also has a great blog with an active community of people using the BBS approach. To see an example of what this type of workout looks like, check out this video on YouTube. For an in-depth video presentation about BBS, watch this video.
- The Power of 10: The Once-A-Week Slow Motion Fitness Revolution, by Adam Zickerman & Bill Schilley. This is more of a nuts-and-bolts book, with less theory than BBS and more focus on teaching you how to do this type of workout. It also has specific routines that can be performed at home, on the road and without access to a gym. The approach is slightly different than what’s advocated in BBS, but the basic idea is the same.
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Great article. You really should take a look at MovNat
Actually our ancestors were long distance runners. Look at aborigines and africans. Also, I’ve never seen a fat long distance runner.
Exactly! That’s where the article kind of lost me. Anyone who actually knows how our ancestors hunted would know that for much of human history and almost all of human evolution revolved around long distance endurance running. I have started running at a steady pace for an hour a day and have seen wonderful results in my energy, waste size and overall health. Studies are not always reliable. Factors are often left out.
Id just figured this out on my own today! I remembered that all throughout highschool I was healthy and fit. I did whatever came natural to me and didnt follow diets or workouts. Well what came naturally to me back then was to eat when hungry, not worrying much about calories and fat. I did alot of low intensity dance class and walking everywhere, with sprints of running thrown in a few times a day. Mostly outside. And some dumbbells, crunches, etc. Thats it. Fast forward to 30 and ive been doing the “chronic cardio” gym thing and its not working. Plus id rather be outside walking in different parks. Im going to go back to my highschool method and see how it goes!
So your saying the my extremely skinny best friend has been doin normal every day things and not workin out, while I’ve been working my ass off running two miles a day, and she gets to still be skinny while I suffer with no weight loss?
hi Chris, I’d recommend having a look at what MovNat does. Their approach and that of other physical educators who looked back at more practical and natural training methods has done huge things to change the way we train our endurance athletes but not by the exact methods recommended by McGuff.
McGuff’s books is excellent but it lacks certain layers that I think you’ll find in MovNat. More than any other player in the fitness industry they have a true experiential competency in what natural movement actually means and how it is executed. Unsurprisingly there is not a gym necessary nor a bench-press in sight.
Chris, I know it’s been a while since you wrote this, but what do you think about sprinting or another high intensity, high impact activity like full court indoor basketball if someone has arthritis? If you know of anyone who can answer this, or if you can, it would be greatly appreciated.
I began following Doug Mcguff’s high intensity weight training recommendations after watching a utube video lecture that I stumbled across serendipitously one day. I have done an aproximate “Big 5” (after which I play a little racquetball) to failure within 12 minutes between once a week and 2 weeks since May of this year. As a middle aged woman who had been athletic when young I was surprised at how much strength I had lost when I first began this very spare and focused routine. I could only bench press 90 lb.s and overhead 40 lb.s! When young I could bench press over 150 lb.s without working out..so I could lift my weight basically. Now, 6 months later, I’m benching 130 lb.s 5 times and overheading 70 lb.s 10 times! I don’t do leg presses because I have a hurt right knee. But, the most amazing thing is that although I didn’t change my basically good diet I have lost 16 lb.s! I don’t keep a scale around but when I saw my doctor yesterday she informed me of the sixteen pound weight loss.
I can hardly believe that exercising as infrequently and briefly, albeit very intensely, as I do I have still made so much progress and even lost a significant amount of weight. I know it makes sense in theory but I just can’t take in the reality of it yet :)! I have to repeat that I took Doug Mcguff’s words to heart and lift weight carefully yet ferociously! I work really hard when I sit down to do bench presses, overheads, pulldowns and 2 different rows. I remember that Doug stated that the body needs to interpret the workout as “threatful” and even frightening. Well, this high intensity approach has worked in real life! My blood pressure is down and I just feel a lot more viable everyday. I understand that my body is making concrete repairs and improvements when I’m resting in between workouts. I only exercise (frisbee or dancing in the kitchen:)) when I feel like it. I have more respect for my body after taking in the principles of Body By Science, which I bought after viewing the lectures. Thanks to all those exercise/sports researchers who questioned conventional “wisdom”! My gratitude to Doug Mcguff and John Little!
Perfect common sense information. Get off the treadmill folks, and just move your body! I also have found the Tracy Anderson Method very satisfying as a form of excercise. Use your own body weight against itself, lots of reps, dance, and just have fun!
After reading that, hopefully my customer will not bang to please me doing cardio again!!!!
Blake/Mike/Wow… and several others on here who believe that Chris is somehow contributing to the obesity epidemic in America by “preaching laziness” and “criticizing them for working out”, you all need to learn how to read through content and train your brain to actually think rationally and at least partially intelligently about it’s message before horking your guts out onto your computer screen so you can feel cool on the internet.
Where’s your website Mike? And why do you bother addressing Chris as “Mr. Kresser”. After reading your comments, I had to go shower to wash it all off.
Cmon people. Grow up, seriously.
Chris – I think you should consider following KGH’s lead and turn off reader comments. Even if this penalizes those of us who are aligned with you, so be it, if it spares us from the moronic responses above.
And to you running addicts that are trashing Chris, you might be lean, you might be fit, and you may not have had your comeuppance…yet. Your n=1 experiment doesn’t prove jack. I am 5’11”, 170 lbs and 8% body fat and lost 25 lbs following PaNu without any exercise. My n=1 experiment doesn’t prove jack either. Read Good Calories Bad Calories perhaps in spite of the polysyllabic words and apparently abstruse logic.
Nice differentiation of the issues that we all sort of made out of this article Matt. Good work. Some might disagree with your summary, but I like it!
This discussion has sort of morphed into three simultaneous topics being discussed at the same time.
A. Whether high volume/low intensity cadio is a good way to lose weight
B. Whether high volume/low intensity cardio training is healthy
C. Whether high volume cardio/low intensity training is necessary for an endurance athlete
The answer to A. is that it isn’t. People think it is because they subscribe to the calorie balance model. If you want to burn the most calories then high volume/low-intensity cardio does this the best. But we know that the calorie balance model is completely broken. You have to manage the hormones. High volume cardio fails in this regard.
And B is related to A. High volume cardio is catabolic (muscle wasting) and pro-inflammatory – not good in the hormone department. I’m sure there is a group of people out there who can thrive on it, but for the general population it is ineffective in terms of training economy and results. Is it better than nothing? Sure. But for the great majority of the population, weight training is superior. It’s scalable, functional, variable, and effective in short amounts of time 2-3 times per week.
C is a whole different subject. If you are an endurance athlete should you do high volume cardio? Absolutely. But this has nothing to do with health. Competitive athletes are interested in winning, not in being healthy. I advocate weight lifting for health, but I readily admit that power lifters can be some of the most unhealthy “athletes” there are. What I recommend and what they do diverge as the level of competition rises. My suspicion is that a lot of endurance athletes do way too much long and slow training, but they have to do some for sure.
Any kind of high volume training is bad for health really – intervals (CrossFit) or even weight lifting. It’s just that cardio seems to be abused more than others for no good reason.
Joe Bloe – guess you actually believe Calories In / Calories Out is the “cause” of weight loss? Maybe you should read Good Calories Bad Calories.
Truth – your name is irony at its finest. Thanks for the “insightful” comment.
This article is pathetic. I run over 100 miles a week and I have considerably more energy when I’m in high training than when I’m not. Additionally high volume training absolutely works for weight loss. I eat everything I want all the time and I maintain 5% body fat. Before I became a runner, I was about 20% body fat, no matter what I ate. When I contracted mono and had to take off 4 months, I gained 20 pounds despite restricting myself to a “normal” 2500 calorie diet. I started running again and voila, everything returned to normal faster than it was put on. I have much better energy levels when I exercise and my health is absolutely great. I’ve had one injury in 8 years of running and beyond the mono, I haven’t had anything beyond a normal common cold. The average American is a fat pathetic loser. The human body is designed for endurance, more than almost any other creature, and anyone that claims otherwise as an excuse to not exercise is just another fat pathetic loser.
No offense, but you seem like a jerk. I personally believe that weight training is better for people than endurance exercise (and takes less time), but I don’t intend to condemn people that choose a different lifestyle than my own. Guess I can’t say the same for you. Oh, and I also have 5% body fat, and I never run endurance.
This is more of a bash of the article than people who do exercise other than running. Even as a runner (50-70 mpw), I realize it can be monotonous and that not everyone actually enjoys it like I do. I’ve come to accept that. But this article makes it sound like if you run a lot, you could drop dead at any moment! First…
Our ancestors came out of the trees and started walking upright so they could run! And run a lot.
Any runner will also tell you that the more they run, the slower their heart rate becomes. That is because a cardiovascular activity like running STRENGTHENS THE HEART. It does it in the same way that bench pressing will strengthen your pectoral muscles. You stress the muscle (heart) by keeping it an elevated rate for an extended peariod of time, then you rest it for how ever many hours you take between runs, or other activity. During this time it rebuilds any torn fibers, etc. and becomes slightly stronger each time. When your heart becomes stronger, it can move a higher volume of blood with each stroke. Because of this, the heart does not need to beat as fast to get the required amount of blood to the rest of the body. In a way, when your heart beats less, you are putting less mileage on your heart. It is basically the same as a car engine. Which one is more likely to fail, the one with 200,000 miles (beats), or the one with 150,000 miles (beats)? That’s a good start…
The whole premise of this article is bull. Our ancestors lived to be about 30. Let’s do better than that.
Running promotes stronger bones, stronger cardio vascular system, increases muscle and burns fat. But you have to run MORE than 30min before fat burning occurs, 90min before fat is the primary source of fuel. To lose weight, you have to increase exercise (whatever it is) and keep calorie consumption the same or decrease. In other words: Calories consumed minus calories burned must be consistently negative to lose weight. It is not rocket science, but neither is this pseudo science article.
Americans want a get rich quick or lose weight without working out scheme. Thanks for pretending to give it to them
This whole cardio v weights debate is akin to “Paleo” only and “LowCarb” diets only. There are several variations of each which work and they are not blanket recommendations that apply to every single individual.
I work with elite endurance athletes – Tour de France riders, World Class Triathletes, Marathon Runners etc. I can tell you they are 1. not overweight 2. not dying from heart disease. Their bodyfat is typically 5-8%, they train up tp 25 – 30hrs per week, and blood profiles will typically show low inflammatory markers and normal immune markers. There are of course other factors that determine this such as nutrition obviously, recovery, periodization, genotype, inclusion of resistance/anaerobic training phases etc.
There are umteen studies on how endurance exercise improves insulin sesitivity, upregulates lypolysis, decreases cholestrol, strengthens immunity, the list goes on. There are studies that show that endurance exercise can prevent telomere shortening and thus prolong aging… Tarnopolsky recently published a study on this.
I find those that “dis” the whole idea of cardio exercise are those that have never actually experienced it and practiced it. I do agree, in terms of recommending forms of exercise to sedentary or obese people, that resistance/HIIT training is superior. However, simply blanketing everyone with the same brush, in a simliar way to nutrition recommendations, is just wrong.
Finally, for some good old “anectodotal” evidence… surely cardio exercise can’t be too bad if you want to look like this 😉 http://www.ultramarathonman.com/flash/
I read Chris’ article again and I fail to find him mentioning weights (though he did use the phrase “weight machine”). It seems to me he wrote the article about interval training as a method to lose weight, and mentioned it was better than cardio exercises for that purpose. He did mention machines though, and that started a lot of reader comments about machines vs free weights. And since he compared interval training to cardio, he got some comments defensive of cardio training.
So I have more or less been ignoring comments that are comparing methods of stressing the muscles (free weights vs machines), as I am mostly interested in the technique that Sisson calls high intensity interval training (HIIT), since it is claimed to be superior to traditional cardio exercise “in almost every way”.
Have you investigated HIIT with respect to training elite endurance athletes? From what I’ve read, HIIT is supposed to increase endurance in far less time than pure cardio exercise, and therefore be an advantage in endurance training, so I’m wondering what you find wrong with HIIT. Since, in your post you were defensive of cardio, but didn’t compare it with HIIT in that defense, I now have the idea that you haven’t investigated the benefits of HIIT. Here’s a reference I would like your comments on:
If you read this short link, and then the other Mercola link within, it definitely gives the idea that not only is that particular method of interval training great at inducing weight loss and increasing cardiovascular health, but it gives superior endurance to what one can gain from pure cardio exercise alone, and in less time. I would appreciate it if you will comment on this as an endurance expert, and please include any experience you may also have in using HIIT to train your clients.
I understand Chris is not simplying saying “do weights, not cardio”, but its essentially what the article alludes to. This is the general theme amongst most of the current top practicioners in this community.. Mark Scisson, Rob Wolff etc. I’ve read all the books and articles.
Of course we have investigated HIIT and use it extensively during different training phases. And yes, we are well aware of the studies showing improved training adapations in terms of anaerobic v aerobic training. There are several good papers that have shown improved gene expression, AMPK pathways etc with HIIT over aerobic exercise. However, there are many other factors that need to be taken into account in terms of optimising endurance capacity… cardiac hypertrophy, Type 1 synthesis, cappillarization, oxygen delivery, … factors which are improved with endurance training. Not only that, but excessive HIIT training is damaging and is simply counter productive. Physiologically its not optimal, if it was, then we wouldn’t have Tour de France cyclists doing 5-6hr rides or Marathon runners doing 2-3hr runs.
I understand this discussion is not related to elite endurance athletes. However, the principles underlying the “cardio v HIIT/weights” debate still do apply. Leaving aside the pro athletes, just take a look at those that compete at the various events such as any Ironman, Cyling or Ultra Distance running events around the globe. There are literally millions of healthy, fit, lean individuals that use endurance exercise as there main form of training.
So I agree that HIIT is beneficial. I also agree and stated in my first comment, it is a more effective form of exercise for the obese/sedentary. Like all health, nutrition and exercise debates… its all about context and its all about taking into account several factors. That said, writing off endurance exercise as some form of heart disease causing, health damaging form of exercise is a little naive in my opinion.
Thanks Barry – a very informative reply and what I had hoped for, as I couldn’t imagine someone working with world class athletes not exploring HIIT and determining its strengths and weaknesses!
So it seems that if one tried to push for either endurance OR HIIT to the exclusion of the other, especially as regards, say, endurance athletes, it would not make sense, as, to varying degrees they both are beneficial. I feel resolved about that issue now, thanks to you.
So the issue possibly is only, should cardio need to be totally excluded (to protect our heart, etc.?) if one undertakes a HIIT program. Maybe that is what Chris implied. But he didn’t say that explicitly. He just said it doesn’t work for weight loss, and gave 3 reasons. Personally, I’d rather take the moderate approach and assume a person can exercise however they wish, including cardio, even if their main goal is weight loss and maintenance of muscle, with minimal destruction or aging. But they should consider Chris’ point that they won’t effect weight loss from the cardio exercise they do. For me, that is the important issue. Also, as Chris says, “The effects of overtraining are real, and documented in the scientific literature.” He said this regarding CF, but I’m wondering if it isn’t also a concern when a non-athlete, interested only in weight loss, decides between cardio and HIIT programs. It seems that the briefer hours alone would tend to protect a novice from many of the dangers lurking in cardio exercise. Do you have any guidelines along this line? I appreciate your help.
it’s simple. Do a bit of both.
doing “cardio” a couple of days a week will not cause you any of the so called “health risks”… combine it with some HIIT and you get the best of both worlds
As a triathlete, i’m very aware of the excessive oxidative stress and inflammation training can cause so before i train i make sure that i take a pretty complete bio shake (raw egg whites, pro-biotic kefir, blueberry, strawberry, blackberry, raspberry, cherries, coconut oil, 100% cocoa, DMAE powder and cinnamon) and immediately after training i take a cold shower to rapidly reduce my body temperature, take a baby aspirin and drink a potent green tea.
it seems to work pretty well
any comments or anything to add to this?
Thanks for the response. I’m sure it’s not the first (or last) time you’ll get in trouble for an opinion. That’s why I like your blog!
I’ll probably get myself in trouble with the CF crowd here, but I don’t think that kind of training (high intensity workouts several days in a row) is beneficial over the long-term – and in fact is harmful. I have several CF folks as patients right now that have trashed their adrenals (and thus the rest of their body) by overtraining. The effects of overtraining are real, and documented in the scientific literature.