How to Preserve Exercise Hormesis

We all know exercise is ultimately good for us, but nonetheless, places inseparable stress on the body, imposing thermal, metabolic, hypoxic, oxidative, and mechanical stressors. Ultramarathon runners generate so many free radicals during a race that they can damage the DNA of a significant percentage of their cells. Researchers have looked at the exercise-induced increase of free radical production as a paradox: why would an apparently healthy act—exercise—lead to detrimental effects through damage to various tissues? This arises out of somewhat of a misunderstanding: exercise in and of itself is not necessarily the healthy act—it’s the recovery after exercise. For example, exercise training has been shown to enhance antioxidant defenses by increasing the activities of our antioxidant enzymes. So, yeah, during the race, ultra-marathoners may be taking hits to their DNA, but a week later may end up better than when they started.

Six days after a race, athletes don’t just go back to the baseline level of DNA damage, but have significantly less, presumably because they had so revved up their antioxidant defenses. So, maybe exercise-induced oxidative damage is ultimately beneficial. It’s kind of like vaccination. By freaking out the body a little, we might induce a response that’s favorable in the long run. In other words, classic hormesis, where low levels of damage can upregulate protective mechanisms and ultimately leave you better off.

Thirty years ago, it was reported that marathon running acutely increased intestinal permeability, meaning the leakiness of one’s gut. Even just 10 minutes of heavy physical activity was found to redistribute enough blood to the peripheral muscles to cause ischemia (oxygen deprivation) in the digestive tract. So, even recreational exercisers may be affected, and, indeed, treadmill running for 20 minutes at 80 percent maximum aerobic capacity or 60 minutes at 65 percent can increase gut leakiness by up to 200 percent. This helps explain why exercise can increase the risk of life-threatening food allergy attacks—food-dependent, exercise-induced anaphylaxis, presumably because the increased leakiness of the intestinal barrier can allow tiny food particles to slip into the bloodstream. But never fear—hormesis to the rescue. Growing evidence suggests that at rest, chronic exercisers have improved gut barrier integrity.

Similarly, the inflammation caused by exercise-induced muscle microtrauma may be necessary for the adaptation that ends up strengthening our muscles. Taking anti-inflammatory drugs, like ibuprofen, during exercise can acutely reduce muscle protein synthesis, though the long-term effects of this are unclear. Taking antioxidant supplements during exercise can reduce the delayed-onset muscle soreness a day or two after a tough workout, but a week later, your muscle performance may suffer compared to those who had instead taken a placebo. A study entitled “Antioxidants prevent health-promoting effects of physical exercise in humans” found that vitamin C and E supplements blocked the eventual boost in antioxidant enzyme expression afforded by exercise. This may explain why athletes mega-dosing vitamin C (over a gram a day) tend to suffer an impairment in sport performance. 

But wait. Might eating anti-inflammatory and antioxidant rich plant foods also undermine these hormetic responses? Before-and-after muscle biopsies show berries can decrease running-induced inflammation, and both acute and chronic consumption of greens has been shown to reduce exercise induced free radical DNA damage. The same was noted for tomato juice. So, was there impaired exercise adaptation? On the contrary, less oxidative stress, but greater performance. And, the same thing with berries—improved strength recovery and some herbs, too. Decreased muscle damage without blocking exercise benefits. So, at least certain whole plant foods appear to offer the best of both worlds.