Medicine

Yes, You Really Can Exercise Too Much

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Have too much of a good thing, and it stops being good. Sunlight raises your vitamin D levels, but too much leads to skin cancer. Kale makes for a nutritious diet, but too much can trigger thyroid problems. Exercise is good for your heart, mind, and waistline, but too much can lead to a dangerous condition called rhabdomyolysis. With intense workouts becoming more popular, doctors are seeing a rise in this life-threatening condition.

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Past The Point Of No Return

Rhabdomyolysis occurs when muscles are pushed to their breaking point — literally. The muscle fibers break down and release loads of the protein myoglobin into the bloodstream. Usually substances like that would be filtered out via the kidneys, but in this case, it's just too much for them to take. As the condition sets in, sufferers feel tired and weak, with stiff, aching, tender muscles. Unfortunately, those symptoms are also your garden-variety signs of a tough workout, but this isn't: the toxic levels of myoglobin turn urine brown. Doctors usually treat it with IV fluids, and it sometimes requires kidney dialysis.

Rhabdo, as it's often called, has been historically associated with physically grueling jobs, like soldiers and firefighters. It's also known to happen with traumatic injuries, since that's another way to break open muscle cells and release myoglobin. But lately, more people have been contracting the condition from recreational workouts. Between 2010 and 2014, a single New York emergency room had 29 cases of exercise-induced rhabdomyolysis, and several papers since have detailed cases of people coming in with the condition after spin classes.

Schematic diagram of myoglobin, a heme-containing protein that participates in oxygen storage in normal muscle but is responsible for kidney damage in rhabdomyolysis.

Know Your Limits

Rhabdomyolysis is most likely to strike people when they're new to an exercise, and it's often people in the best shape who are most at risk. That could be because being physically fit can give you an elevated sense of your abilities, so you're more likely to push yourself during a spin class or CrossFit workout even though you've never done it before. "One thing I've noticed when people tell me they've gotten rhabdo in the gym is that they gave up their personal power," exercise physiologist Joe Cannon told the New York Times. "They kept doing what the instructor told them to do because they did not want to look weak."

That's key to avoiding rhabdo: know your limits, and don't go beyond them. Consider your first few experiences with a new exercise program as a trial run, and keep things light. That could mean you ride that bike more slowly than the veterans in the class, do one set of squats instead of three, or build up your running distance slowly instead of joining a new friend on their weekend 10-miler. It'll be better for you in the long run.

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What Happens If You Exercise Too Much?

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