On that spring day across America, the CrossFit faithful gathered--and toiled. There were hundreds of thousands of them, certainly. Maybe a million, maybe two. In an old industrial facility in New Orleans, they hoisted themselves on gymnastic rings and did dips up there. In a strip mall in Santa Cruz, California, they threw 20-pound medicine balls against a wall over and over again. In a business park near the Dulles airport in Virginia, they pushed weighted barbells above their heads, first once a minute, and then as fast as they could for three minutes straight--or until they couldn't lift their arms.
Excluding foods. The exclusion of entire categories of commonly eaten foods like whole grains and dairy requires frequent label reading in the supermarket and in restaurants. It may also increase the risk of deficiencies such as calcium, vitamin D, and B vitamins, if these nutrients are not consistently eaten from the allowed foods or a vitamin supplement. For example, there are some nondairy calcium-rich foods that are absorbed well by the body such as collard and turnip greens or canned bone-in sardines and salmon, but you would have to eat five or more servings of these greens and fish bones daily to meet recommended calcium needs. (Note that some greens like spinach that are touted to be calcium-rich also contain oxalates and phytates that bind to calcium so very little is actually absorbed.) One small, short-term intervention study of healthy participants showed a 53% decrease from baseline in calcium intake after following a Paleo diet for three weeks.  Furthermore, the exclusion of whole grains can result in reduced consumption of beneficial nutrients such as fiber and thus may increase one’s risk for diabetes and heart disease.
The Paleo diet not only misunderstands how our own species, the organisms inside our bodies and the animals and plants we eat have evolved over the last 10,000 years, it also ignores much of the evidence about our ancestors' health during their—often brief—individual life spans (even if a minority of our Paleo ancestors made it into their 40s or beyond, many children likely died before age 15). In contrast to Grok, neither Paleo hunter–gatherers nor our more recent predecessors were sculpted Adonises immune to all disease. A recent study in The Lancet looked for signs of atherosclerosis—arteries clogged with cholesterol and fats—in more than one hundred ancient mummies from societies of farmers, foragers and hunter–gatherers around the world, including Egypt, Peru, the southwestern U.S and the Aleutian Islands. "A common assumption is that atherosclerosis is predominately lifestyle-related, and that if modern human beings could emulate preindustrial or even preagricultural lifestyles, that atherosclerosis, or least its clinical manifestations, would be avoided," the researchers wrote. But they found evidence of probable or definite atherosclerosis in 47 of 137 mummies from each of the different geographical regions. And even if heart disease, cancer, obesity and diabetes were not as common among our predecessors, they still faced numerous threats to their health that modern sanitation and medicine have rendered negligible for people in industrialized nations, such as infestations of parasites and certain lethal bacterial and viral infections.
CrossFit gyms use equipment from multiple disciplines, including barbells, dumbbells, gymnastics rings, pull-up bars, jump ropes, kettlebells, medicine balls, plyo boxes, resistance bands, rowing machines, and various mats. CrossFit is focused on "constantly varied, high-intensity, functional movement," drawing on categories and exercises such as calisthenics, Olympic-style weightlifting, powerlifting, Strongman-type events, plyometrics, body weight exercises, indoor rowing, aerobic exercise, running, and swimming.