Author | Chris Kresser 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. Regular movement protects us from disease in several ways, but most importantly it prevents oxidative damage and inflammation – the primary mechanisms underlying most modern, degenerative diseases. 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.1
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.2 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.3 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.4 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.5
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 neurodegeneration6
Overtraining is especially damaging because of its effects on cortisol. We discussed cortisol at length in Step 6: Manage Your Stress,7 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.8
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.9
No cardio? Then what should we do instead?
In short, we should move like our ancestors. They didn’t strap on a heart monitor and take off for a 45-minute jog, nor did they go down and swim laps for an hour in the local lake. Yet they were extremely fit and almost entirely free of the modern diseases that plague us today.
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 from 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,10 we should:
- Move frequently at a slow pace
- Lift heavy things and sprint occasionally
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. Spending time outdoors reduces stress, increases vitamin D levels, and brings us pleasure, joy and a sense of connection with the world around us.
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) or HIT in the case of sprints and high intensity training (HIT) in the case of strength training.
Several studies have been done comparing HIIT to medium-intensity, steady-state exercise, and HIT has been shown to be superior in nearly every meaningful marker.
In one study, one group was assigned to “cardio” exercise, 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.11
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.12
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.13 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 “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,14 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 HIT, as opposed to just a few hours with low-intensity training.
HIT also activates hormone-sensitive lipase (HSL), which mobilizes fatty acids for energy use. This means that during HIT, both glucose and fatty acids will be burned, leading to greater fat loss and restoration of insulin sensitivity.
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 HIT
There are many books on the subject, but these are the two I’d recommend for most people:
- Body By Science by Doug McGuff.15 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.16 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.17This 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.
- http://wholehealthsource.blogspot.com/2008/05/exercise-didnt-keep-us-from-getting-fat.html ↩
- http://www.ajcn.org/content/early/2010/09/29/ajcn.2010.29471.full.pdf+html ↩
- http://www.sciencedirect.com/ ↩
- http://journals.lww.com/acsm-msse/Abstract/2010/06000/Behavioral_Compensatory_Adjustments_to_Exercise.23.aspx ↩
- http://epublications.bond.edu.au/cgi/viewcontent.cgi?article=1049&context=hsm_pubs ↩
- http://conditioningresearch.blogspot.com/2011/01/dont-exercise-too-much.html ↩
- Step 6: Manage Your Stress ↩
- http://www.paleonu.com/panu-weblog/2009/11/1/cardio-causes-heart-disease.html ↩
- http://eurheartj.oxfordjournals.org/cgi/content/full/29/15/1903 ↩
- http://www.marksdailyapple.com/primal-blueprint-fitness/#what-is-pbf ↩
- http://www.nature.com/ijo/journal/v32/n4/abs/0803781a.html ↩
- http://jap.physiology.org/content/98/6/1985.long ↩
- http://jp.physoc.org/content/588/6/1011 ↩
- Body By Science ↩
- Body By Science ↩
- http://www.bodybyscience.net/home.html/ ↩
- http://www.amazon.com/Power-Once-Week-Revolution-Harperresource/dp/006000889X ↩