Don’t Want to Get Sick? Back Off the CrossFit

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Back to back hard days can hurt your immune system.Getty Images

If your hand calluses are a source of pride, or you named your dogs Cindy, Fran, and Murph, a recent study published in Frontiers in Physiology was conducted with you and your immune system in mind.

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PHOTOS: 12 CrossFit Workouts Anyone Can Do

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A group of Brazilian researchers set out to examine the effects of consecutive CrossFit workouts on the body’s muscle power, blood lactate, glucose, and cytokines, which are proteins that can be pro- or anti-inflammatory. Nine conditioned men with at least six months of CrossFit experience participated in two high-intensity WODs (workouts of the day) over the course of 48 hours. Each subject submitted to blood tests and a muscular-power assessment before and after the training sessions.

While the researchers found that the back-to-back workouts had no negative impact on muscle power, they did see a significant decrease in anti-inflammatory cytokines. In other words, the high-intensity WODs came at a cost, and the subjects’ immune systems picked up the tab. A weakened immune system can make you feel more rundown, and also makes you more susceptible to colds and the flu. (As for long-term effects, the researchers say more longitudinal studies are warranted, but we can only guess that continuously logging intense back-to-back sessions — or three, four, or five workouts in a row, regularly — beats up the immune system even more.)

While these current findings are valid, they aren’t so new or surprising. Pete McCall, adjunct faculty in Exercise Science at Mesa College, says this research only confirms what trainers and fitness professionals should know and apply to their own programming. “Unless there’s a very specific performance goal” — say, if you were a professional athlete, with a dialed in diet and sleeping 10 hours a night. “I’m never going to have anybody do more than two or three high-intensity workouts in a week,” McCall says. In fact, he recommends reducing the intensity of group fitness classes between Thanksgiving and Christmas because it’s a time of year when clients are already stressed and may be working with compromised immune systems.

McCall notes that this immunity risk isn’t unique to CrossFitters. “The same information would be true if someone was doing a high-intensity SoulCycle three to five times a week,” he says.

So what does it mean for your unlimited class package? The good news is that you can still hit up the box most days of the week, but be strategic and thoughtful about training: Limit high-intensity days to two, or at most three, a week.

A workout qualifies as high-intensity when you rely less on your oxidative energy systems, which utilize oxygen, and more on the anaerobic energy systems, the metabolic pathways you tap into for activities like sprints or, say, 21 barbell thrusters. Exercise physiologists use blood lactate levels (a byproduct of high-intensity exercise) to measure intensity, but you can use something far simpler: rate of perceived exertion (RPE). Consider an RPE of 1 “sitting on the couch,” and an RPE of 10 “emptying the tank,” and log no more than three workouts at a level 8 to 10 a week. You can still get the blood pumping and break a sweat on the other days, but keep your RPE between 5 and 8.

Most CrossFit coaches use this type of training method (called periodization) in their programming, working athletes through varying cycles of volume and intensity, or offering multiple WODs that vary according to experience or level of conditioning. But, ultimately, staying healthy comes down to exercising personal responsibility, and sometimes that means a bit of old-fashioned restraint. 

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