It's often touted as "healthy" in the eyes of conventional wisdom, and, if you've had the pleasure of taking a health class at any point in your life, you're probably quite familiar with the purported benefits of this over-hyped exercise.
If you couldn't guess from the title of this post the exercise to which I'm referring, I'm talking about "cardio."
In particular, I mean long distance cardio (think endurance work done at a moderate to high intensity for up to an hour+, sometimes every day of the week).
Now, I'm not opposed, nor will I ever be, to any mode of exercise that takes a chronically sedentary person from couch potato to avid fitness enthusiast. If you take an overweight/obese individual, put them on a treadmill for an hour a day thus causing them to be more active than they were previously, said person will likely lose some fat and have some amount of improvement in health. However, eventually you start to incur diminishing returns.
This point of diminishing returns is where we must draw the line between healthy activity and chronic stress.
To further extrapolate this line to which I'm referring, consider this:
* Evidence suggests that endurance athletes may be at an increased risk in comparison to the general populace to suffer from atrial fibrillation (that's a fast and irregular heartbeat) (1). This puts them at a higher risk for suffering from a stroke and/or experiencing cognitive decline (2).
* Meanwhile, light to moderate exercisers are at a lower risk for developing these health issues (3).
** In comparison to others, marathoners (a group we might expect to be exemplars of health and fitness) are at an increased risk for developing atherosclerosis (4, 5, & 6), thus putting the at risk for developing other health woes such as stroke and dementia (7).
*** Long distance/duration efforts, furthermore, seem to cause a good amount of oxidative damage in participants (8), which may be fine in the short term (after all, we get better by enduring a stressor then adapting to it), but if taken to a chronic extreme, your body has scant chance of adequately adapting.
**** Moderate exericise seems to improve the fat loss of overweight individuals, while more intense exercise seems to induce a compensatory response, causing subjects to eat more and expend fewer calories post workout (9).
***** In general, there seems to be an eventual trade-off between health and performance if you take things too far (10).
So what should we do? Just sit on our buts all day?
Of course not! There are excellent alternatives to getting up in the morning and running four miles (something I used to do 6 days a week, and to my own detriment I might add).
Let's take a second now and consider our options. I think this wonderful categorization of cardio types (courtesy of Mark Sisson) will do just the trick:
So let's take a minute to break this down:The benefits of low level aerobic work (walking, hiking, cycling, swimming)- increases capillary network (blood vessels that supply the muscle cells with fuel and oxygen)- increases muscle mitochondria- increases production of fat-burning and fat-transporting enzymes- more fun, because you can talk with a partner while doing itThe benefits of interval training (sprinting in short intense bursts)- increases muscle fiber strength- increases aerobic capacity (work ability)- increases muscle mitochondria (the main energy production center in muscle)- increases insulin sensitivity- increases natural growth hormone productionThe costs of chronic (repetitious) mid- and high-level aerobic work- requires large amounts of dietary carbohydrates (SUGAR)- decreases efficient fat metabolism- increases stress hormone cortisol- increases systemic inflammation- increases oxidative damage (free radical production)- boring!
* Exercises like walking can be a much more preferable alternative to slaving away on a treadmill for an hour. I'm all for this! I would much rather go for an easy walk than kill myself (in a misguided design for the sake of my health). Some evidence even suggests that walking is just as effective as a vigorous run in terms of risk reduction for hypertension, high cholesterol, and diabetes (11).
** Additionally, high intensity intervals such as sprinting can effectively increase muscle fiber strength, increase our aerobic work capacity, increase muscle mitochondria, increase insulin sensitivity (meaning we can better metabolize and partition carbohydrates), and up our natural growth hormone production.
Note: lifting weights can also be an effective tool for improving one's metabolic health (12).
*** We ought to avoid chronically over-stressing ourselves via "chronic mid- and high-level aerobic work." Otherwise we increase our risk for a host of health issues. Furthermore, if building muscle is a concern of yours, the systemic inflammation induced by chronic cardio can hamper your ability to recover from a weight training session (13), thus, your ability to grow muscle will be hampered.
I think the best course of action seems pretty obvious: Do a lot of low level walking, sprint or do some sort of high intensity interval workout every once in while, and don't make running marathons a career.
So what's your take on this?
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