The Truth about Extreme Exercise, Oxidative Stress, and Your Health

If you’re a committed athlete and health nut, you’ve probably heard it said that your training may be endangering your health.

More often than not, the article or video (or sales page) will claim that the oxidative stress caused by your intense training is increasing your risk of heart disease and cancer, making you age faster, and possibly, causing you to die sooner.^(1-3)

The idea is that intense training produces more free radicals than moderate exercise, which may “overwhelm antioxidant defenses” and cause “irreparable oxidative damage… potentially resulting in ill health and/or disease,” writes Dr. Kelsey Fisher-Wellman, the author of a review published in 2009.⁽⁴⁾

Before we dive into the evidence, let’s examine what oxidative stress is.

Oxidative Stress: A Quick Primer

During normal metabolism, your body produces unstable molecules, free radicals being the most common. These molecules can damage your cells and create more free radicals, causing more damage.

Your body uses different antioxidants to control free radical (oxidative) damage. The two main kinds of antioxidants are endogenous (produced inside your body) and exogenous (consumed from diet and other sources).

When free radicals overwhelm your antioxidant defenses, your cells are damaged. This damage is called oxidative stress.^(5,6)

There’s still some question as to whether or not oxidative stress accelerates aging.^(7-11) However, most data indicate that excessive and chronic oxidative stress may cause cellular damage and contribute to atherosclerosis, heart disease, cancer, dementia, and many other diseases.^(12-18)

Why Oxidative Stress Isn’t Always Bad

When we first discovered that free radicals existed in humans, they were quickly blamed for aging and other diseases.⁽¹⁹⁾

Contrary to what researchers first thought, we now know that oxidative stress is beneficial in small amounts. In fact, it’s essential. Newer research has shown that oxidative stress prompts your cells to become stronger over time by increasing your body’s antioxidants.⁽²⁰⁾

Free radicals also serve as important signaling molecules for a number of functions in your body, so getting rid of them entirely would likely be counterproductive.⁽²¹⁾ 

All forms of exercise cause some oxidative stress.⁽²²⁾ This is probably one of the reasons it makes you healthier. Your body is slightly weakened, recovers, and becomes more resistant to oxidative stress from the next workout (or other stressors).^(23-30)

Most researchers agree that moderate exercise produces healthy amounts of oxidative stress, to the point they call it an antioxidant.⁽³¹⁾

The concern is that doing more than that may have the opposite effect.

When Exercise May Be too Much of a Good Thing

Your body has a limited capacity to increase its antioxidants and control free radicals.

Some researchers believe that long, intense exercise (especially endurance training) may cause more oxidative stress than humans can handle.⁽³²⁾

“Heavy and sustained exercise training generates large quantities of free-radicals that likely outstrip the buffering capacity of the system, leaving these individuals susceptible to oxidative stress…” writes Harshal R. Patil, the author of a recent review on this topic.⁽³³⁾

This is thought to be true “even in superbly trained individuals.”⁽³⁴⁾

In theory, your body runs out of antioxidants during extreme exercise. Free radicals overwhelm your cells and oxidative stress rises far beyond healthy levels. Over time, this damage increases your risk of heart disease, cancer, and an early death.

Dr. James O’Keefe, the author of a review on how endurance exercise affects heart health, states it this way:⁽³⁵⁾

“If we went out for a run right now and you ran hard… by 60 minutes something starts happening… the free radicals blossom, and it starts burning the heart. It starts searing and inflaming the inside of your coronary arteries.”⁽³⁶⁾

Every athlete has a limit to how much oxidative stress they can handle. The question is whether or not extreme exercise can push your body past this point.

Before we look at the research, let’s define “extreme” exercise.

What is “Extreme” Exercise?

If you ask most researchers in this field, the answer will probably be “whatever causes lots of oxidative damage.”

The problem with with this definition is that any kind of exercise can cause oxidative damage.⁽³⁷⁾ If your training is challenging, it’s probably causing significant oxidative stress, regardless of your sport.⁽³⁸⁾

This is true for:

• Strength training.^(39-42)
• Sprinting.⁽⁴³⁾
• Motocross.⁽⁴⁴⁾
• Indoor rock climbing.⁽⁴⁵⁾
• Running.^(46-49)
• Cycling.^(50-53)
• Swimming.⁽⁵⁴⁾
• Rowing.^(55,56)
• Kayaking.^(57,58)
• Canoeing.⁽⁵⁹⁾
• Soccer.^(60,61)
• Tennis.⁽⁶²⁾
• Football.^(63,64)
• Rugby.^(65,66)
• Handball.⁽⁶⁷⁾
• Martial arts.^(68,69)
• Volleyball.^(70,71)

Some limited data also indicates that oxidative stress may contribute to fatigue. If this is the case, it’s possible that any workout that can make you tired will probably cause some oxidative damage.⁽⁷²⁾

Is Endurance Exercise Especially Bad?

Endurance sports often get the most blame for being “extreme” or “excessive” when it comes to oxidative stress.

Mitochondria (the “power plants” of cells) are believed to be one of the main sources of free radicals. Endurance sports use more oxygen, which sends more energy through your mitochondria. In theory, the higher your metabolic rate and energy needs, the more free radicals your mitochondria will produce.^(73,74)

However, free radicals are also created through other pathways, and are not always related to your oxygen needs.⁽⁷⁵⁾ Several studies have shown that despite much higher oxygen intakes during aerobic exercise, anaerobic exercise (sprinting, weight lifting, etc) can produce similar levels of oxidative damage.^(76,77)

Studies that didn’t measure oxygen consumption have also found similar levels of oxidative damage after strength and endurance training.^(78,79)

That said, it’s generally possible to do more endurance training, which will probably create more free radicals over time. No athlete runs sprints for six hours straight, but many pro cyclists ride their bikes that long every day.

On the other hand, there are a lot of bodybuilders, football players, and other physique or mixed sport athletes who train several hours a day.

For the rest of the article, we’ll loosely define “extreme” exercise as anything that has you working at a moderate to high intensity for more than about 1-2 hours per day, endurance or not, endurance or otherwise.

Now let’s see if this kind of training is bad for you.

What the Evidence Says About Extreme Exercise and Oxidative Stress

Despite many inconsistencies and problems with the research, most data indicate that hard exercise increases oxidative stress.^(80-84)

However, long-term studies, as opposed to short-term, have shown that extreme training can increase your body’s antioxidant levels which can help prevent and repair oxidative damage.^(85-88)

According to Dr. Karl-Heinz Wagner, “during exercise… ROS [free radicals] formation can stimulate adaptive mechanisms… which can lead to decreased oxidative damage or apoptosis [cell death],” in a review published in 2011.⁽⁸⁹⁾

In one study, untrained people ran five times per week, for an hour at a time, at  80% of their maximum heart rates (basically, the definition of “chronic cardio”). There was an increase in lipid peroxidation and oxidative stress at the beginning of the study. Twelve weeks later, however, the runners had less lipid peroxidation, higher antioxidant levels, and less oxidative stress than before the study.⁽⁹⁰⁾

Most people wouldn’t call five hours per week of running “extreme,” but other studies have shown the same adaptations can occur with much more training.

With consistent training, the “capacity of the body will expand or adapt; ultimately leading to improvements in health and/or human performance,” continues Dr. Wagner.

Endurance athletes are able to prevent or at least minimize oxidative stress after races and brutal training periods. The rise in oxidative stress is moderate to nonexistent, and usually goes back to normal hours or days later.^(91-103)

Oxidative damage sometimes occurs, but it’s minimal.⁽¹⁰⁴⁾ It’s also repaired quickly and most data indicate there is no lasting harm.^(105,106)

Multiple studies have shown that after Ironman triathlons, well-trained athletes have a large decline in DNA damage for about three weeks.^(107-109) The researchers believe this is thanks to “the upregulation of repair mechanisms and enhanced endogenous antioxidative systems.”⁽¹¹⁰⁾

In other words, their training increased their body’s ability to prevent and repair DNA damage, largely by increasing its antioxidant defenses.

It’s also likely this boost in antioxidant defenses protects against oxidative stress from “non-exercise related conditions.”⁽¹¹¹⁾

That is, if you get stuck in an elevator with someone reeking of cigarettes, your body will probably suffer less damage than if you weren’t training like nuts.

Animal studies have also shown that exhaustive and moderate exercise helps increase antioxidant levels and protect against oxidative stress.^(112-117)

Elite endurance athletes (who train more than almost anyone) also tend to live longer than the average population, although it’s impossible to tell if this is from better antioxidant protection or other reasons.^(118-120)

That said, at least one study has found higher levels of oxidative damage in well-trained endurance athletes at rest.⁽¹²¹⁾

This is misleading, however, because the athletes had done a hard race two days before being tested, and it’s possible this wasn’t enough time for them to recover. Even so, they were better protected against some markers of oxidative stress after exercise than healthy non-athletes.

Most other studies have also shown similar or lower levels of oxidative stress in athletes compared to healthy non-athletes.^(122,123)

Before you decide to do an Ironman or become Mr. Olympia however, understand that boosting your antioxidant levels often requires a lot of training.

How Much Should You Train to Protect Your Body?

This depends on what you’re training for.

If you exercise only for health, you don’t need to train three hours a day to be well protected against oxidative stress.

Moderate endurance and strength training can significantly reduce oxidative stress and increase your antioxidant defenses.^(124-131)

It’s a different story if you’re a competitive athlete. You probably need to train more to protect yourself.

A low-volume training plan might be fine if your event is short, but it’s probably not best for longer or more intense competitions. It takes a lot of hard training to increase your antioxidant levels enough to protect you from something like an Ironman or marathon.⁽¹³²⁾

“The training programme must be sufficiently long and intense to trigger a consequent adaptive response of the antioxidant system and a decrease of oxidative stress,” writes Dr. Julien Finaud, the author of a 2006 review.⁽¹³³⁾

If you don’t train adequately, your antioxidant system may not be strong enough to protect you from permanent oxidative damage if you suddenly increase your training volume. In other words, being a “weekend warrior” may not be ideal.⁽¹³⁴⁾

One study found a large increase in oxidative damage after a football game. The the researchers concluded that “higher amounts of physical activity may be required” to protect them from this kind of exercise.⁽¹³⁵⁾

Athletes with the highest training volumes, experience, and fitness often have higher antioxidant levels and lower levels of oxidative stress.^(136-138) Well-trained cyclists are also better able to minimize oxidative stress after a workout than amateurs.⁽¹³⁹⁾

Small amounts of endurance training can also increase your Vo2max before it significantly raises your antioxidant levels.⁽¹⁴⁰⁾ Basically, you can get fitter without necessarily being better protected against oxidative stress.

In one of the studies mentioned previously, Ironman athletes were well protected against oxidative stress after training 13 hours per week.⁽¹⁴¹⁾ Other data have shown that triathletes training 14-17 hours per week were able to manage the oxidative stress from their workouts.^(142,143)

That’s a lot of training, but minimal considering it took these athletes around 10-12 hours to finish an Ironman.

If your training is consistent and specific to your sport, it will probably increase your antioxidant levels enough to protect you from excessive oxidative damage. 

Of course, you can still overdo your training.

How Much is Too Much?

Some authors have suggested that there is an “optimal level of exercise” and that  extreme training “exceeds the currently undefined optimal level.”⁽¹⁴⁴⁾

The problem with this notion of an “optimal level of exercise” is that it’s relative to the individual and changes over time.

If an elite Ironman triathlete were to to do a two hour bike ride, they’d probably experience almost no oxidative stress. For them, that’s an easy workout.

If a couch potato who hasn’t exercised in 30 years were to do the same workout, it might cause far more damage.

Oxidative stress is not necessarily dependent on how much you exercise, but how much you do relative to your current ability level. 

In untrained people, intense, moderate, and light exercise all cause about the same amount of oxidative damage.⁽¹⁴⁵⁾

According Dr. Niels Vollaard, the author of a review published in 2005, oxidative stress is “desired, or even a required consequence of exercise, which is controlled to such an extent that it occurs whenever the relative exercise intensity is sufficiently high, regardless of training status.”⁽¹⁴⁶⁾

For example, professional cyclists often train over 1,000 hours per year — over 3 hours per day, and at times, 30-40 hours per week. Considering the demands of their sport, this might be “optimal.”

They tend to have higher antioxidant levels than amateur cyclists and healthy non-athletes. Their antioxidant levels are also increased at the end of a 20 day stage race, suggesting they handled the oxidative stress well.⁽¹⁴⁷⁾

Other studies have also found that well-trained cyclists are able to control the  oxidative stress from intense training and racing.^(148-151)

If you push yourself outside of your comfort zone, you’re probably going to experience some oxidative stress. If you do too much, you might hurt yourself. If you don’t do enough, you may not be protected from higher training loads and other sources of oxidative stress.

This process “can be seen as no different from other responses to exercise: a certain load disturbs homeostasis, resulting in adaptations in the body to be able to cope with a similar load in the future,” writes Dr. Vollaard.⁽¹⁵²⁾

Some athletes beat themselves into the ground with too much volume, intensity, or both. In these cases, it’s possible oxidative stress may play a role in overtraining.^(153,159)

Luckily, it’s usually not hard to tell when this is happening. Overtraining makes you sick, anxious, and moody. It destroys your sleep, performance, appetite, and libido. It also perpetuates sore or fatigued muscles, causes injuries, and usually makes you feel horrible.^(160-163)

If that sounds familiar, you’re doing too much.

The Truth about Extreme Exercise, Oxidative Stress, and Your Health

Every kind of hard exercise creates free radicals that cause some oxidative damage.

This damage is quickly repaired, and sparks adaptations that make you more resistant to oxidative damage from high volume and/or intensity training.

With more training, your body increases its antioxidant levels to control the additional free radicals, generally keeping oxidative stress within safe limits.

It’s possible to hurt yourself by overtraining, and oxidative stress may be part of this process. However, it’s not news that overtraining is bad for you. High volume training is also not the same thing as overtraining.

If you train smart by providing enough stimulus to progress, but not so much that you overtrain, the oxidative stress from your training will probably not damage your health.

At present, “there are no indications that exercise-induced oxidative stress has any negative impact on health…,” according to Dr. Vollaard.⁽¹⁶⁴⁾

As with fatigue, muscle soreness, and any other response to exercise, oxidative stress should not be avoided, but managed with smart, consistent training.

You don’t need to do extreme athletics to be healthy.

On the other hand, if you do train hours a day for extreme sports, you probably don’t have to worry about it damaging your health or shortening your life. It might even make you healthier.

Most evidence indicates that if you train in a progressive, intelligent manner, with adequate recovery between workouts, you can build up to extremely high training loads and still be protected against potentially dangerous levels of oxidative stress.

You’re reading Part 5 of a series on whether or not exercise damages your heart. Click here to read Part 6.

You can read the first post in this series by clicking here.

A special thanks to Drs. Monica Pittaluga, Richard Bloomer, Hilmi Orhan, and Zsolt Radak for their assistance in making this article possible.

 

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80. Vollaard NB, Shearman JP, Cooper CE. Exercise-induced oxidative stress: myths, realities and physiological relevance. Sports Med. 2005;35(12):1045-62. Abstract: https://pmid.us/16336008 | Full Text: https://goo.gl/hTQaS | Author Contact: <N.Vollaard@hw.ac.uk>

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82. Knez WL, Coombes JS, Jenkins DG. Ultra-endurance exercise and oxidative damage: implications for cardiovascular health. Sports Med. 2006;36(5):429-41. Abstract: https://pmid.us/16646630 | Full Text: https://goo.gl/Xn3yt

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86. Knez WL, Jenkins DG, Coombes JS. Oxidative stress in half and full Ironman triathletes. Med Sci Sports Exerc. 2007 Feb;39(2):283-8. Abstract: https://pmid.us/17277592 | Full Text: https://goo.gl/5uqlb

87. Knez WL, Coombes JS, Jenkins DG. Ultra-endurance exercise and oxidative damage: implications for cardiovascular health. Sports Med. 2006;36(5):429-41. Abstract: https://pmid.us/16646630 | Full Text: https://goo.gl/Xn3yt

88. Vollaard NB, Shearman JP, Cooper CE. Exercise-induced oxidative stress: myths, realities and physiological relevance. Sports Med. 2005;35(12):1045-62. Abstract: https://pmid.us/16336008 | Full Text: https://goo.gl/hTQaS | Author Contact: <N.Vollaard@hw.ac.uk>

89. Wagner KH, Reichhold S, Neubauer O. Impact of endurance and ultraendurance exercise on DNA damage. Ann N Y Acad Sci. 2011 Jul;1229:115-23. doi: 10.1111/j.1749-6632.2011.06106.x. Abstract: http:/pmid.us/21793846 | Full Text: https://goo.gl/1YlBW

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97. Shing CM, Peake JM, Ahern SM, et al. The effect of consecutive days of exercise on markers of oxidative stress. Appl Physiol Nutr Metab. 2007 Aug;32(4):677-85. Abstract: https://pmid.us/17622282 | Full Text: https://goo.gl/4CguF

98. Serrano E, Venegas C, Escames G, et al. Antioxidant defence and inflammatory response in professional road cyclists during a 4-day competition. J Sports Sci. 2010 Aug;28(10):1047-56. Abstract: https://pmid.us/20686993 | Full Text: NA

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102. Knez WL, Jenkins DG, Coombes JS. Oxidative stress in half and full Ironman triathletes. Med Sci Sports Exerc. 2007 Feb;39(2):283-8. Abstract: https://pmid.us/17277592 | Full Text: https://goo.gl/5uqlb

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105. Neubauer O, Reichhold S, Nersesyan A, et al. Exercise-induced DNA damage: is there a relationship with inflammatory responses? Exerc Immunol Rev. 2008;14:51-72. Abstract: https://pmid.us/19203084 | Full Text: https://goo.gl/s0fhs

106. Wagner KH, Reichhold S, Neubauer O. Impact of endurance and ultraendurance exercise on DNA damage. Ann N Y Acad Sci. 2011 Jul;1229:115-23. doi: 10.1111/j.1749-6632.2011.06106.x. Abstract: http:/pmid.us/21793846 | Full Text: https://goo.gl/1YlBW

107. Reichhold S, Neubauer O, Veronika E, et al. No acute and persistent DNA damage after an Ironman triathlon. Cancer Epidemiol Biomarkers Prev. 2008 Aug;17(8):1913-9. Abstract: https://pmid.us/18708380 | Full Text: https://goo.gl/YYqbC<

108. Reichhold S, Neubauer O, Hoelzl C, et al. DNA damage in response to an Ironman triathlon. Free Radic Res. 2009 Aug;43(8):753-60. doi: 10.1080/10715760903040628. Abstract: https://pmid.us/19591014 | Full Text: NA

109. Wagner KH, Reichhold S, Hölzl C, et al. Well-trained, healthy triathletes experience no adverse health risks regarding oxidative stress and DNA damage by participating in an ultra-endurance event. Toxicology. 2010 Dec 5;278(2):211-6. doi: 10.1016/j.tox.2009.09.006. Epub 2009 Sep 18. Abstract: https://pmid.us/19766696 | Full Text: Requested.

110. Reichhold S, Neubauer O, Veronika E, et al. No acute and persistent DNA damage after an Ironman triathlon. Cancer Epidemiol Biomarkers Prev. 2008 Aug;17(8):1913-9. Abstract: https://pmid.us/18708380 | Full Text: https://goo.gl/YYqbC

111. Fisher-Wellman K, Bloomer RJ. Acute exercise and oxidative stress: a 30 year history. Dyn Med. 2009 Jan 13;8:1. doi: 10.1186/1476-5918-8-1. Abstract: https://pmid.us/19144121 | Full Text: https://goo.gl/QMo47

112. Oztasan N, Taysi S, Gumustekin K, et al. Endurance training attenuates exercise-induced oxidative stress in erythrocytes in rat. Eur J Appl Physiol. 2004 May;91(5-6):622-7. Epub 2003 Dec 18. Abstract: https://pmid.us/14685869 | Full Text: NA

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117. Fisher-Wellman K, Bloomer RJ. Acute exercise and oxidative stress: a 30 year history. Dyn Med. 2009 Jan 13;8:1. doi: 10.1186/1476-5918-8-1. Abstract: https://pmid.us/19144121 | Full Text: https://goo.gl/QMo47

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122. Knez WL, Jenkins DG, Coombes JS. Oxidative stress in half and full Ironman triathletes. Med Sci Sports Exerc. 2007 Feb;39(2):283-8. Abstract: https://pmid.us/17277592 | Full Text: https://goo.gl/5uqlb

123. Knez WL, Jenkins DG, Coombes JS. Oxidative stress in half and full Ironman triathletes. Med Sci Sports Exerc. 2007 Feb;39(2):283-8. Abstract: https://pmid.us/17277592 | Full Text: https://goo.gl/5uqlb

124. Cakir-Atabek H, Demir S, PinarbaŞili RD, et al. Effects of different resistance training intensity on indices of oxidative stress. J Strength Cond Res. 2010 Sep;24(9):2491-7. doi: 10.1519/JSC.0b013e3181ddb111. Abstract: https://pmid.us/20802287 | Full Text: NA

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128. Radak Z, Chung HY, Goto S. Systemic adaptation to oxidative challenge induced by regular exercise. Free Radic Biol Med. 2008 Jan 15;44(2):153-9. doi: 10.1016/j.freeradbiomed.2007.01.029. Epub 2007 Jan 23. Abstract: https://pmid.us/18191751 | Full Text: Received from author.

129. Majerczak J, Rychlik B, Grzelak A, et al. Effect of 5-week moderate intensity endurance training on the oxidative stress, muscle specific uncoupling protein (UCP3) and superoxide dismutase (SOD2) contents in vastus lateralis of young, healthy men. J Physiol Pharmacol. 2010 Dec;61(6):743-51. Abstract: https://pmid.us/21224506 | Full Text: https://goo.gl/pFHwB

130. Campbell PT, Gross MD, Potter JD, et al. Effect of exercise on oxidative stress: a 12-month randomized, controlled trial. Med Sci Sports Exerc. 2010 Aug;42(8):1448-53. doi: 10.1249/MSS.0b013e3181cfc908. Abstract: https://pmid.us/20139793 | Full Text: https://goo.gl/PcLYx

131. Fatouros IG, Jamurtas AZ, Villiotou V, et al. Oxidative stress responses in older men during endurance training and detraining. Med Sci Sports Exerc. 2004 Dec;36(12):2065-72. Abstract: https://pmid.us/15570141 | Full Text: https://goo.gl/kY7lK

132. Finaud J, Lac G, Filaire E. Oxidative stress: relationship with exercise and training. Sports Med. 2006;36(4):327-58. Abstract: https://pmid.us/16573358 | Full Text: https://goo.gl/zH48t

133. Finaud J, Lac G, Filaire E. Oxidative stress: relationship with exercise and training. Sports Med. 2006;36(4):327-58. Abstract: https://pmid.us/16573358 | Full Text: https://goo.gl/zH48t

134. Chang CK, Tseng HF, Hsuuw YD, et al. Higher LDL oxidation at rest and after a rugby game in weekend warriors. Ann Nutr Metab. 2002;46(3-4):103-7. Abstract: https://pmid.us/12169852 | Full Text: NA

135. Rudarli Nalçakan G, Nalçakan M, Var A, et al. Acute oxidative stress and antioxidant status responses following an American football match. J Sports Med Phys Fitness. 2011 Sep;51(3):533-9. Abstract: https://pmid.us/21904294 | Full Text: NA

136. Margaritis I, Tessier F, Richard MJ, et al. No evidence of oxidative stress after a triathlon race in highly trained competitors. Int J Sports Med. 1997 Apr;18(3):186-90. Abstract: https://pmid.us/9187972 | Full Text: NA

137.  Martinovic J, Dopsaj V, Dopsaj MJ, et al. Long-term effects of oxidative stress in volleyball players. Int J Sports Med. 2009 Dec;30(12):851-6. doi: 10.1055/s-0029-1238289. Abstract: https://pmid.us/20013555 | Full Text: NA

138. Knez WL, Jenkins DG, Coombes JS. Oxidative stress in half and full Ironman triathletes. Med Sci Sports Exerc. 2007 Feb;39(2):283-8. Abstract: https://pmid.us/17277592 | Full Text: https://goo.gl/5uqlb

139. Mena P, Maynar M, Gutierrez JM, et al. Erythrocyte free radical scavenger enzymes in bicycle professional racers. Adaptation to training. Int J Sports Med. 1991 Dec;12(6):563-6. Abstract: https://pmid.us/1797698 | Full Text: NA

140. Finaud J, Lac G, Filaire E. Oxidative stress: relationship with exercise and training. Sports Med. 2006;36(4):327-58. Abstract: https://pmid.us/16573358 | Full Text: https://goo.gl/zH48t

141. Reichhold S, Neubauer O, Veronika E, et al. No acute and persistent DNA damage after an Ironman triathlon. Cancer Epidemiol Biomarkers Prev. 2008 Aug;17(8):1913-9. Abstract: https://pmid.us/18708380 | Full Text: https://goo.gl/YYqbC

142. Knez WL, Jenkins DG, Coombes JS. Oxidative stress in half and full Ironman triathletes. Med Sci Sports Exerc. 2007 Feb;39(2):283-8. Abstract: https://pmid.us/17277592 | Full Text: https://goo.gl/5uqlb

143. Knez WL, Coombes JS, Jenkins DG. Ultra-endurance exercise and oxidative damage: implications for cardiovascular health. Sports Med. 2006;36(5):429-41. Abstract: https://pmid.us/16646630 | Full Text: https://goo.gl/Xn3yt

144. Fisher-Wellman K, Bloomer RJ. Acute exercise and oxidative stress: a 30 year history. Dyn Med. 2009 Jan 13;8:1. doi: 10.1186/1476-5918-8-1. Abstract: https://pmid.us/19144121 | Full Text: https://goo.gl/QMo47

145. Moflehi D, Kok LY, Tengku-Kamalden TF, et al. Effect of single-session aerobic exercise with varying intensities on lipid peroxidation and muscle-damage markers in sedentary males. Glob J Health Sci. 2012 May 23;4(4):48-54. doi: 10.5539/gjhs.v4n4p48. Abstract: https://pmid.us/22980341 | Full Text: https://goo.gl/FbLpa

146. Vollaard NB, Shearman JP, Cooper CE. Exercise-induced oxidative stress: myths, realities and physiological relevance. Sports Med. 2005;35(12):1045-62. Abstract: https://pmid.us/16336008 | Full Text: https://goo.gl/hTQaS | Author Contact: <N.Vollaard@hw.ac.uk>

147. Mena P, Maynar M, Gutierrez JM, et al. Erythrocyte free radical scavenger enzymes in bicycle professional racers. Adaptation to training. Int J Sports Med. 1991 Dec;12(6):563-6. Abstract: https://pmid.us/1797698 | Full Text: NA

148. Shing CM, Peake JM, Ahern SM, et al. The effect of consecutive days of exercise on markers of oxidative stress. Appl Physiol Nutr Metab. 2007 Aug;32(4):677-85. Abstract: https://pmid.us/17622282 | Full Text: https://goo.gl/4CguF

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