You may know that I am not a big fan of aerobic training. In fact, I don't think there's any good benefit that you can get from aerobic training that you can't get from strength training or anaerobic sprinting, and there are some key negative health effects. Indeed, did you know that aerobic exercise increases oxidative stress, chronically elevates cortisol, and has been shown to lower testosterone levels in men. Even more concerning, intense aerobic exercise in animals decreases reproductive organ size and function, while lowering androgens and causing extreme oxidative stress!

How can it be that aerobic exercise is so bad, when doctors and health professionals are encouraging everyone to do it? There are some legitimate benefits of aerobic exercise, especially for specific populations, such as individuals with high blood pressure, the obese, the sedentary, or those with significant visceral belly fat. The point is that there are substantial negatives that go with aerobic training that many people fail to realize, and those  harmful effects can be avoided by doing strength training or anaerobic system training. In this article, I'll show you the bad news about aerobics, but don't worry, at the end you'll find three bits of good news to set you straight.

Next week, look for a part 2, which will show you some fascinating strategies to alleviate the negative effects of aerobic exercise, with tips on how to train for better health.

High cortisol also makes you age faster because it increases oxidative substances in the body that produce inflammation all over, including in the brain, heart, gastrointestinal tract, and reproductive organs. Oxidants or free radicals are the opposite of the antioxidants that are in "superfoods",  such as raspberries and cherries that fight inflammation. It's well known that exercise raises cortisol because exercise stresses the body, which in the case of strength training is a good thing because it stresses the body to grow or adapt and get stronger. The key is that with strength training , just as cortisol may increase, so will anabolic hormones that build muscle in order to completely overwhelm any negative impact of cortisol. Errors in programming can lead to problems with this ratio, but in general, this is not the case with strength training. In contrast, aerobic training stresses the body without boosting the anabolic hormones, resulting in an overall catabolizing, inflammation-causing situation.

A new study in Psychoneuroendocrinology showed evidence of long-term high cortisol levels in experienced aerobic endurance athletes. Researchers tested hair cortisol in 304 endurance athletes (long-distance runners, triathletes, cyclists), and compared their measurements with a control group of no- athletes. They used hair to test cortisol because it provides evidence of cumulative cortisol secretion over prolonged time.

Results showed that the aerobic athletes had significantly higher cortisol levels compared to controls, and there was a positive correlation between higher cortisol levels and greater training volume. The athletes had long-term elevation of the hypothalamic-pituitary-adrenal axis, which can have detrimental influence on mental and physical health. Researchers write, "These data suggest that repeated physical stress of intensive training and competitive races among endurance athletes is associated with elevated cortisol exposure over prolonged periods of time."

Chronic inflammation occurs when the cells are being repeatedly attacked by oxidative free radicals, elevated insulin, or high cortisol, to name a few. That's why aerobic training causes chronic inflammation-your body produces free radicals in response to the oxygen-rich environment created by increased respiration that goes with aerobic training, and your cortisol is raised from repeated physiological stress.

It's well established that aerobic exercises causes oxidative stress-a review article in the Journal of Sports Science provides a useful summary of how strenuous aerobic exercise induces oxidative stress  that can overwhelm antioxidant defenses. There's widespread and accepted evidence of chronic inflammation from aerobic exercise as seen from increase in free radicals, damage to lipids and DNA , and decreased blood measurements of antioxidants such as glutathione.

What's revealing is there's a wealth of fascinating new research that shows how to protect aerobic exercisers from the negative health effects of their sport! A new study in Current Microbiology tested the effects of probiotics on oxidative stress from aerobic exercise. The purpose of the study was to establish that aerobic exercise causes chronic oxidative stress and that probiotics can be taken to support antioxidant levels and fight the negatives of aerobic exercise. 

Participants were semiprofessional cyclists, and researchers tested the effect of training on oxidative stress and assessed whether supplementing with a probiotic could decrease the negative health effects of aerobic cycling training. They used a control group that only trained and didn't take a supplement and an exercise/supplement group that took probiotics daily. The study ran for four weeks.

Researchers found that intense aerobic training induced oxidative stress in the form of reactive oxygen species and there was evidence of lipid peroxidation, which increases inflammation. Taking the probiotic supplement decreased oxidative stress levels and increased antioxidant activity in the exercise/supplement population, indicating that probiotics can also protect against the negative health effects of aerobic exercise.

This study used a control group that did no exercise and took no supplement, an exercise group, and an exercise/supplement group. The exercise and exercise/supplement groups performed three hours of swimming a day, five days a week for four weeks. The exercise/supplement group was given a dose of 50 mg per kg of body weight a day of vitamin E. Take note that this is a fairly high volume of exercise, but it is likely that any elite aerobic athlete, or even a long-distance recreational trainee-would perform such large amounts of aerobic training.

After four weeks of exercise, researchers found the exercise group had a significant decrease in the size of the reproductive organs (testes and accessory sex organs) and lower levels of testosterone, luteinizing hormone, and related androgen markers. Additionally, the exercise group had significant evidence of oxidative stress in the testes in the form of elevated MDA and lower glutathione. None of these effects were found in the control group, and the exercise/supplement group did not show significant changes in these areas, with no statistically significant increase in oxidative stress.  Antioxidants are suggested as a reasonable supplement to decrease the damaging health effects of aerobic exercise.

A second study supports these findings-both that intense aerobic swimming leads to oxidative stress and reproductive dysfunction in rats and that antioxidants can protect against the damage. The antioxidants tested in this study were zinc and selenium, and the detrimental effects on the rat's health from the aerobic exercise was very similar to the previous study. Researchers also found that there was a significant increase in cortisol in the exercise group, which was not seen in the control group or the exercise/supplement group.

It is likely researchers consider the evidence of acute inflammation and cortisol elevation to be safe for two reasons. First, they are looking at the immediate physiological response to aerobic exercise and are not considering the effects of repeated, prolonged aerobic stress. Second, the population studied had no aerobic training experience, and there is significant evidence that in the untrained or the unhealthy, aerobic exercise may improve some measurements of health in the long-term. As I said at the beginning of this article, there are legitimate benefits of aerobic training-but if you do it over and over again, the benefits decrease and the negatives take over (cortisol, inflammation, and fat gain).

Be aware that there are ways to moderate the negatives of aerobic training. I've already mentioned supplementing with antioxidants and probiotics as proven ways to counteract the bad things aerobic exercise does to you, but simply adding a strength training program may also work. A research group from Turkey tested the effects of different strength training protocols on chronic inflammation. They found that both a hypertrophy and strength protocol resulted in lower inflammatory biomarkers in subjects after completing the different protocols for six weeks. MDA was lower, while glutathione was higher-glutathione will be lower as oxidative stress increases.  Resting glutathione levels increased after six weeks for both protocol groups, pointing to additional protective benefits of resistance training.

Researchers suggest that endurance athletes who are considering taking antioxidants to decrease oxidative stress may be better served by performing resistance training instead. Although this strategy hasn't been tested, the benefits of resistance training for endurance athletes have been proven: a better testosterone to cortisol ratio, greater strength, improved neuromuscular function, and possibly decreased inflammatory biomarkers.

Part 2: How To Counter The Many Negatives of Aerobic Training