Exercise is one of the best things you can do for your body to fight inflammation and stay healthy, but in a seeming paradox, working out also triggers oxidative stress — a main cause of inflammation.
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Oxidative stress is a state in which your body has an imbalance of free radicals and antioxidants, explains Lance Dalleck, PhD, professor of exercise and sport science at Western Colorado University and spokesperson for the American Council on Exercise.
"An excess of free radicals can damage our DNA, leading to muscle breakdown, fatigue, accelerated aging, heart disease, diabetes and cancer," Dalleck says. Meanwhile, antioxidants help protect your cells against free radicals in your body.
So does that mean you should scale back on your workouts? The short answer is no. Free radicals are a natural byproduct of consuming oxygen during exercise (or any activity) to break down ATP (short for adenosine triphosphate) for energy, he says.
Some exercise-induced oxidative stress can actually enhance your health because it conditions your body to adapt to stressful situations. But like all things, too much oxidative stress from exercise can be harmful.
We called up experts to shed some light on oxidative stress and exercise.
Oxidative Stress (and Exercise) 101
To understand the link between oxidative stress and exercise, it's important to understand how oxidation happens. Let's back-track a bit.
Free radicals are molecules that have an extra electron. Oxidation happens when free radicals try to get rid of their extra electron, explains Scott Powers, PhD, a professor of applied physiology and kinesiology at the University of Florida College of Health & Human Performance and a leading researcher on exercise-induced oxidative stress.
Free radicals like to have neutral charges (equal positive and negative particles), so to compensate, they try to ditch their extra electron or steal a proton (positive charge) from another molecule to stabilize themselves, injuring other molecules along the way.
"That's potentially damaging because it can disrupt the normal function of the molecules, causing them to unfold and not work properly," Powers says. This is where antioxidants step in. Antioxidants are oxidation fighting substances that prevent free radicals from damaging other molecules by sacrificing their own electrons, according to Harvard Health Publishing.
Because oxidative stress can lead to a surplus of free radicals (creating an imbalance with antioxidants), it can trigger inflammation associated with chronic diseases, including heart disease, type 2 diabetes and cancer. Research also shows that oxidative stress is associated with neurodegenerative diseases such as Alzheimer's, according to a May 2016 review in Biomedical Reports.
And get this: Exercise is also a cause of oxidative stress. After all, that's exactly what exercise is — a stress to your system.
The Benefits of Exercise-Induced Oxidative Stress
Free radical formation from exercise isn't necessarily a bad thing. Whether you're doing light-, moderate- or vigorous-intensity exercise, there's no evidence that the slight increase in oxidative stress poses a health risk, Powers says. (FYI, free radicals are also a natural byproduct of regular cellular functions in the body, like breathing and eating, according to Harvard Health Publishing.)
And, research has actually the short-term increase in oxidative stress from exercise is a good thing for your body and overall health.
A January 2020 study in Sports Medicine found that DNA damage occurs in the 24 hours following intense endurance exercise. But several days later, the damage was no longer there. Researchers believe that the body's antioxidant reserve — bolstered by exercise — repaired the damage.
"Exercise increases the production of antioxidant enzymes, not only in the muscle that's active during exercise but other organs around the body," Powers says.
You get antioxidants from eating nutritious foods, but your body's own cells also produce antioxidants, like glutathione — which helps combat cellular damage during the aging process. And exercise can help boost the creation of these types of antioxidants.
Case in point: Older adults who regularly exercised had higher levels of glutathione than those who were sedentary, according to an August 2014 study in Free Radical Biology and Medicine.
This means that exercise can help temper potential harm from a whole variety of other stressors. "Even for people who are smokers or living with overweight, obesity or hypertension [high blood pressure] — if they exercise, they have less risk for all-cause mortality than those who have zero risk factors but don't exercise," Dalleck says.
Bonus: The burst of free radicals produced during a workout directs your body to make more ATP, which gives you added energy for exercise and supports muscle contraction, enhancing your athletic performance, Dalleck says.
The Risks of Exercise-Induced Oxidative Stress
When it comes to exercise and oxidative stress, it may not pay to be extra with your workouts. Doing workouts outside of your own fitness level, focusing only on high-intensity exercise and skimping on recovery between workouts can do more harm than good.
When you do these things, you create more free radicals than antioxidants, which creates an imbalance.
"Under normal circumstances, free radicals are likely important trigger signals that allow cells to adapt to various stressors and synthesize the proteins they need to remain healthy," Powers says. "But damage occurs when there's a chronic high production of free radicals."
5 Ways to Reap the Benefits of Oxidative Stress Without the Risks
The bottom line is that the cellular stress that exercise produces is generally good for your health. It's when you overdo it that it becomes harmful, especially when compounded by other factors, like smoking, poor diet and drinking too much alcohol.
What "overdoing it" looks like varies from person to person. But here are some ways to train wisely to prevent the production of too many free radicals and find a balance.
1. Do Workouts at Your Fitness Level
Your workout should be challenging enough to trigger an increase in your body's antioxidant activity — yet not so long or hard that the surge of free radicals overwhelms your system.
"If an activity is too intense for your fitness level, it will be detrimental," Dalleck says, pointing out that you should do interval training, in particular, at your own pace.
Be sure to alternate days between low- and high-intensity workouts to allow your muscles to recover, and bake in one to two rest days per week, according to the American Council on Exercise (ACE).
2. Gradually Increase Intensity
But what if you want to push yourself? "You need to raise the intensity gradually in order to give your antioxidant capacity time to increase commensurately," Dalleck says. "Otherwise you could create too many free radicals for your body to handle."
Try increasing the intensity of your workouts by 5 percent, per the ACE.
3. Listen to Your Body
If you have muscle soreness that lasts longer than a couple of days post-workout, are feeling fatigued instead of energized after exercise and have funky sleep patterns — either snoozing more than usual or waking up frequently during the night, these are signs that you might be overdoing exercise, Dalleck says.
So make sure to take the appropriate amount of rest days in between your workouts.
4. Practice Proper Recovery
"We produce oxidative stress during an exercise session, and recovery is when your body makes all those adaptations to boost antioxidant absorption," Dalleck says.
If you haven't given yourself a chance to fully rest, then your body is still in a state of stress and you won't reap the benefits. The right amount of recovery time varies from individual to individual and depends on the intensity of your workout.
5. Limit High-Intensity Exercise
The jury is still out on whether high-intensity exercise could potentially be harmful. A September 2020 Journal of Sport and Health Science study co-authored by Powers found "there is no convincing evidence that prolonged, high-intensity exercise results in tissue damage and impaired physiological function."
That said, doing a max of two to three high-intensity workouts, such as HIIT, per week is more than enough for most people to reap the benefits of exercise-induced oxidative stress. Some people may be able to do high-intensity exercise more often, but it depends on the duration of the workout and your fitness level and body's overall stress levels, Dalleck says.
For example, completing a Tabata (which is typically just four minutes long) or REHIIT (reduced exertion high-intensity interval training) won't elicit nearly the same degree of stress when compared with a hardcore 45-minute session.
A highly athletic individual will also have greater antioxidant activity to combat high-intensity-exercise-induced oxidative stress than someone who has little recent workout experience. "This will influence your ability to recover more quickly or slowly," Dalleck says.
- Sports Medicine: "DNA Damage Following Acute Aerobic Exercise: A Systematic Review and Meta-Analysis"
- Harvard Health Publishing: "On Call: Exercise and Free Radicals"
- Journal of Sport and Health Science: "Exercise-Induced Oxidative Stress: Friend or Foe?"
- Free Radical Biology and Medicine: "Roles of Sedentary Aging and Lifelong Physical Activity in Exchange of Glutathione Across Exercising Human Skeletal Muscle"