What does science say about this popular workout phenomenon?

By Charlie Williams
Published October 21, 2020

Key Takeaways

Do you know someone who does CrossFit? Then you’ve probably heard how great it is. Don’t know anyone? You’ve still probably heard about this workout phenomenon, which is as pervasive in real life as it is on social media. 

CrossFit gyms, also known as “boxes,” began cropping up in 2000. Now, there are about 13,000 locations globally, plus thousands of photos and videos of CrossFit athletes and muscle-bound influencers flooding social media feeds, making it one of the biggest fitness trends in the world. 

Head to CrossFit’s official website and you’ll find that the program is self-branded as “the key to health and fitness”—one that can be used to “accomplish any goal, from improved health to weight loss to better performance.”

CrossFit provides remarkable results and helps people build athleticism. A quick scroll through the CrossFit hashtag on Instagram or Twitter suggests as much. But what does the science say?

The CrossFit philosophy

CrossFit employs a “jack of all trades, master of none” approach to fitness. The program’s goal is to help participants excel at general physical preparedness, rather than specialized abilities, like those of a long-distance runner or baseball player.

General physical preparedness is achieved through training designed to enhance 10 physical qualities: cardiovascular/respiratory endurance, stamina, strength, flexibility, power, speed, coordination, agility, balance, and accuracy. Trainers emphasize specific weights, distances, completion times, and movement types, to ensure performance is measurable. 

Competition is baked into CrossFit workouts, too. The system mimics athletes’ competitive experiences. CrossFit athletes play the parts of star athletes and devoted fans, cheering on peers during their workouts and receiving loud encouragement from others as they move through high-intensity exercises themselves. If that’s not enough, there’s always the CrossFit Games, where athletes compete for the title of Fittest Man and Woman on Earth. 

Finally, CrossFit brands itself as a lifestyle, rather than a fitness program. Participants are encouraged to eat low-carb, no-sugar diets and socialize within the CrossFit community. “People encourage and motivate each other in every class as they work toward their goals,” the CrossFit website reads. “Start training with friends. Make new friends. The fun is in the community.”

But does CrossFit work?

The minds behind CrossFit have done an excellent job building a successful business (worth $4 billion in 2015)—one that participants evangelize. But recent research and criticism throws aspects of CrossFit’s effectiveness into question. 

A 2018 systematic review and meta-analysis published in the journal Sports Medicine Open found that data to support the fitness platform’s benefits were sparse. Researchers identified 31 relevant studies, included only four, and eventually found that only two had a high level of evidence at low risk of bias. 

These studies reported on body composition, psycho-physiological parameters, musculoskeletal injury risk, life and health aspects, and psycho-social behavior—but scientists were unable to find significant results in any of these variables. There was one upside, however. Preliminary data suggested that CrossFit practice was associated with higher levels of sense of community, satisfaction, and motivation—each an important factor for well-being. 

Another study published in PLOS One in April, examined the anthropometric, hormonal, and physiological differences between advanced and recreational CrossFit participants, compared with physically active controls. Scientists found that advanced CrossFit participants had roughly 7% lower body fat as well as greater bone and non-bone lean mass, muscle morphology characteristics, isometric strength characteristics, peak aerobic capacity, and 3-minute cycling performance, compared with recreational CrossFitters and active controls. 

“It is possible that [advanced CrossFit athletes’] advantages are simply the result of training for a longer amount of time or creating more opportunities to increase their volume load throughout the week,” researchers wrote. The results are encouraging for those who can perform at a high level, but raise questions about CrossFit’s wider accessibility. CrossFit, for its part, says anyone can do CrossFit, “regardless of age, injuries, and current fitness levels.”  A systematic review published in the journal Workplace Health & Safety aligns with the PLOS One study in many respects. First, those who were experienced in CrossFit performed better and had higher gains in aerobic capacity and anaerobic power than beginners. Data also suggested that CrossFit, like any other high-intensity training, increased strength, musculature, and endurance, while increasing lean body mass. However, researchers suggested that  “Nurses should assess previous injuries and possible limitations prior to recommending CrossFit; nurses can recommend their clients find gyms with On-Ramp programs or classes of basic CrossFit movements used in the workouts.” 

On the plus side, researchers found that risk of injury from CrossFit was consistent with rates of injury for other fitness routines. “Approximately 74% of all runners, for example, experience a moderate or severe injury each year, which is much higher than the injury rate of 19.4% among CrossFit participants,” they wrote.

Another study, published in Sport Sciences for Health, found scientific evidence that CrossFit lives up to 6 out of the 10 general physical skills of athletes it proposes: cardiovascular/respiratory endurance, stamina, strength, flexibility, power, and balance. The other four physical skills—speed, coordination, agility, and accuracy—could not be verified.

A quick word from the critics

Critics claim that CrossFit brings a higher-than-average injury risk, also pointing to a handful of cases of CrossFit-related exertional rhabdomyolysis—a rare pathologic condition caused by muscle breakdown that can kill—to claim that the technique is dangerous. Many also point to questionable decisions from CrossFit’s founder, Greg Glassman, who has been at the helm as CrossFit’s social media accounts published odd posts on hot-button topics like religion and sexuality. However, more data is needed before clear causal links between CrossFit and increased injury risk can be made and the opinions on topics unrelated to fitness of the system’s founder have no bearing on its effectiveness.    

The final word

Anecdotal accounts can leave your head spinning. Many who participate in CrossFit are full-blown evangelists who live the CrossFit code with unwavering dedication. Still others say that CrossFit’s workouts are dangerous and its community emphasis is cult-like. 

The science, on the other hand, paints a more balanced picture. Limited evidence suggests CrossFit is beneficial for those who are capable of performing at a high-level and completing high-intensity workouts. Still, as of yet, the data only supports 60% of the physical skills CrossFit purports to improve. 

While it’s clear that many CrossFitters are reaping big health benefits, the science doesn’t fully support this popular workout—yet. 

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