We’ve never been ones to downplay the wondrous effects of regular exercise. Far beyond weight loss, even a little regular physical activity can have massive health benefits: It boosts your mood and energy, strengthens your heart, decreases headache frequency, prevents diabetes, osteoarthritis and many other chronic diseases, improves your memory and sleep, and decrease your blood sugar and your stress, too. It literally slows aging, and helps you keep your RealAge — the actual age of your body — younger. That’s a lot of good.
But more, more, more is not better when it gets into extremes, and extreme exercise can, in fact, be downright dangerous.
One example: a recent study found that extreme exercise can, frighteningly, lead to blood poisoning. Participants did a range of very intense endurance exercises, like different ultra-marathons run on consecutive days. The researchers compared blood samples before and after that ultra exercise with those of a control group and found that the extreme exercisers developed leaky gut walls, i.e. bacteria were able to leak from the gut into the bloodstream. The effect of this leakage (which you know doesn’t sound good, right?) is a serious infection. (The exception: people who are fit and healthy, and who train regularly to build up to this kind of exercise, and do regular intense but not extreme or prolonged — more than 2 hours at a time — of extreme exercise can develop immunity to this ugly bacterial scenario.)
There is also evidence to suggest that long-term, excessive endurance exercise — marathons, ultra-marathons, ironman triathlons, and the like — can actually damage your joints, your heart and your arteries by overwhelming mitochondrial buffering systems. This might seem counterintuitive, as we’re used to thinking of exercise as good for the heart. This is still true! It’s just that it’s only true up to a point. The reason is that every time you push your body to excess, overloading your cells with demands for energy, it undergoes the same processes as it does with inflammation or a stress response. If you do this once and give your heart a rest, it’s function and arterial reactivity (i.e. how your arteries function) returns to normal within a week. But if you keep pushing your heart with extreme prolonged intense exercise day after day, for months or years at a time, this repetitive injury can cause heart problems.
Again, this certainly doesn’t mean that you should take exercise off the table! Not at all. Remember all those health benefits we listed at the top? The point is rather that exercise, like everything else in life, is not all-or-nothing: good enough is just great. The American Heart Association’s recommendations are a good guideline: 150 or more minutes of moderate aerobic activity a week, or at least 75 minutes of vigorous activity a week, plus muscle-strengthening twice per week. If you’re intent on doing an endurance event, simply take care to train properly.