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The CrossFit stimulus—constantly varied high-intensity functional movement coupled with meat and vegetables, nuts and seeds, some fruit, little starch, and no sugar—prepares you for the demands of a healthy, functional, independent life and provides a hedge against chronic disease and incapacity. This stimulus is elegant in the mathematical sense of being marked by simplicity and efficacy. The proven elements of this broad, general, and inclusive fitness, in terms of both movement and nutrition, are what we term our CrossFit Essentials.

For CrossFit, power is exactly equal to intensity. In a manner similar to the term “functional,” the term “intensity” historically has been nebulously defined, often based on perceived efforts or correlates rather than an objective and measurable assessment. CrossFit’s measure of intensity is power. This is important because now we can establish measurable, observable, and repeatable data from our workouts by calculating intensity.

Read MoreDefining CrossFit, Part 2: Intensity

Individuals on low-carbohydrate diets have lower levels of ingested glucose and smaller liver and muscle glycogen stores. In this 2016 trial, endurance athletes following a low-carbohydrate diet were shown to maintain energy sufficiency during exercise through increased reliance on fat oxidation.

Read MoreGluconeogenesis during endurance exercise in cyclists habituated to a long‐term low carbohydrate high‐fat diet

This trial indicates metformin suppresses gains in strength and muscle mass associated with resistance training in elderly patients. Its results support previous research suggesting the drug suppresses the benefits of resistance training in multiple populations. In patients who do not require immediate improvements in glycemic control, metformin’s suppression of exercise-induced muscle strength and size gains could increase risk of disability and mortality. These risks may provide an argument for not prescribing metformin to elderly patients. In diabetic and prediabetic patients, it is worth considering non-pharmaceutical treatments that lead to improved glycemic control without reducing the benefits of exercise.

Read the article Metformin blunts muscle hypertrophy in response to progressive resistance exercise training in older adults

Oxygen, the very thing that gives us life, can also be life-threatening, under certain circumstances increasing the risk for central nervous system oxygen toxicity (CNS-OT) seizure. CNS-OT seizures are a limitation of both hyperbaric oxygen therapy and scuba diving, particularly among Navy SEALS who use closed-circuit rebreathers. Dr. Dominic D’Agostino, an expert in the neuroprotective effects of the ketogenic diet, explains why ketones were investigated as a possible mitigator of CNS-OT seizures. He also summarizes existing research on the effects of exogenous ketone supplements on CNS-OT, describes the potential mechanisms at work, and lists examples of ketones' protective qualities.

Read MoreKetosis in Extreme Environments: Mitigating Central Nervous System Oxygen Toxicity

In this 2011 trial, resistance exercise is shown to reduce liver fat content even in the absence of weight loss. Resistance exercise improves muscle’s ability to effectively regulate circulating glucose and fat levels, a change that reduces insulin resistance and liver fat buildup. At minimum, this indicates resistance exercise alone may help reverse insulin resistance and fatty liver disease. More importantly, it suggests treatments that induce weight loss, such as other changes to diet and exercise, may drive more rapid and effective metabolic improvements when paired with resistance training.

Read MoreResistance exercise reduces liver fat and its mediators in NAFLD independent of weight loss

This 2012 review summarizes evidence indicating exercise, specifically interval training, maintains or improves skeletal muscle insulin sensitivity and as a result reduces risk of insulin resistance and diabetes. Exercise increases skeletal muscle insulin activity in the obese, while sedentary behavior decreases it. The ability of the muscle to take up and burn fuel (i.e., skeletal muscle oxidative capacity) is a strong predictor of whole-body insulin resistance.

Read MoreExercise and Type 2 Diabetes: New Prescription For An Old Problem

Increasing time spent doing high-impact physical activity as a youth is a simple and direct way to improve skeletal health. One of the programming directives offered at the CrossFit Kids Certificate Course is including impact-loading exercises on a daily basis. This simple addition results in meaningful and significant benefits not only in terms of the improved fitness it generates through these plyometric exercises but also with respect to increased skeletal health in the long term.

Read the articleCrossFit Kids Research Brief: Bone Density

Metabolic training refers to conditioning exercises intended to increase the storage and delivery of energy for any activity. Ultimately, the CrossFit position on metabolic conditioning, or “cardio,” is summed in two points: Anaerobic training can match endurance training for aerobic benefits. Metabolic training with varying and mixed exercise modalities avoids specificity of adaptation allowing for additional first wave-cardiovascular/respiratory adaptations and increased functional strength.

Read the article Metabolic Conditioning

This 2016 trial found that 12 weeks of high-intensity interval training (HIIT) significantly improved cardiometabolic function and liver fat content in diabetic subjects. HIIT subjects saw significant increases in a variety of markers of cardiovascular health, including healthful regeneration of cardiac muscle tissue and improved cardiac contractile capabilities, as well as reversal of certain forms of cardiovascular degeneration associated with Type 2 diabetes. The same subjects also showed a 39% decrease in mean liver fat content, with four of the 11 subjects in the HIIT group seeing a reduction from clinically significant liver fat levels to “normal” liver fat.

Read MoreHigh intensity intermittent exercise improves cardiac structure and function and reduces liver fat in patients with type 2 diabetes

“Given the strong evidence for a direct role of physical activity in the prevention of insulin resistance, and the fact that exercise training increases mitochondrial biogenesis and improves glucose tolerance and insulin action in individuals with insulin resistance and type 2 diabetes, the question of why such a potent modulator of these conditions is not more commonly prescribed is perplexing and should be of utmost concern to medical health care professionals worldwide. To continue to attack the growing health burden by investing almost exclusively in strategies that target secondary and tertiary treatment of chronic disease states (i.e. pharmaceutical interventions) is extremely short sighted: primary defence mechanisms (i.e. exercise/diet and lifestyle interventions) will decrease disease prevalence by preventing these conditions in the first place!”

Read MoreExercise as a therapeutic intervention for the prevention and treatment of insulin resistance

In the final installment of his hyponatremia series, Prof. Tim Noakes describes how three industry-funded studies inadvertently produced data that would prove inconvenient for Gatorade and the Gatorade Sports Science Institute. Together, the studies showed that sodium balance has no impact on the extent to which blood sodium concentration falls during exercise and that abnormalities in the regulation of body water content explain the development of EAH and EAHE. In short, they demonstrated how sports drink marketing had contributed to the EAHE epidemic in the U.S. after 1981. Noakes explains how the studies’ authors generated conclusions that would be more palatable for the industry. He also describes how various scientific journals responded when he began pointing out the studies’ errors.

Read MoreThe Hyponatremia of Exercise, Part 12

Type 2 diabetics and other insulin-resistant individuals commonly exhibit skeletal muscle insulin resistance (i.e., an impaired ability of the muscles to take in glucose from the blood). This highly cited 2002 review illustrates the effect of exercise training on insulin resistance and glucose transport and presents evidence that chronic and acute exercise improve the ability of the muscles to regulate blood sugar levels.

Read MoreInvited Review: Effects of acute exercise and exercise training on insulin resistance

In 1991, Professor Tim Noakes made a discovery that would prove inconvenient for the burgeoning sports drink industry; he discovered that the true cause of EAH and EAHE is abnormal fluid retention during prolonged exercise. The industry, Noakes explains, needed to find a way to justify its continued promotion of the idea that athletes should “drink as much as tolerable” during exercise. As a result, its members created a new myth: the myth of the salty sweater. Industry scientists sought to demonstrate that salty sweaters were in danger of developing salt deficiencies that put them at risk of “hyponatremic dehydration.” In part 11 of his hyponatremia series, Noakes outlines how the Gatorade and the Gatorade Sports Science Institute worked together to market their sports drinks, even if it meant bending the scientific literature to their will.

Read MoreThe hyponatremia of exercise, part 11

Prof. Tim Noakes shares a telling anecdote that demonstrates how Gatorade and the Gatorade Sports Science Institute (GSSI) sought to promote their commercial interests by mischaracterizing dehydration as a medical disease and propagating a fundamental misunderstanding of the causes of hyponatremia. In 2004, Noakes took a quiz on the GSSI website. The quiz was designed to test scientists’ and medical professionals’ knowledge of the factors that cause hyponatremia. Noakes, a foremost expert in the field, failed the quiz, which he determined was a lesson in indoctrination, not real science. Here, he recounts the experience while analyzing the flaws in each of the quiz’s seven questions.

Read MoreThe hyponatremia of exercise, part 10

In Part 9, Professor Tim Noakes describes the sports drink industry’s response to proof that exercise-associated hyponatremic encephalopathy (EAHE) is not due to sodium deficiency and cannot be prevented by drinking electrolyte-containing sports drinks. He explains how he and his colleagues discovered that, rather than resulting from sodium deficiency, EAHE develops from overhydration. He then outlines the preponderance of evidence that demonstrates it is difficult, perhaps even impossible, for humans living in normal conditions to develop a sodium deficiency. Nevertheless, the sports drink industry and its proxies in sports medicine and sports science continued to promote the economically advantageous but scientifically unsupportable overconsumption of sodium-containing drinks during exercise.

Read MoreThe Hyponatremia of Exercise, Part 9

In Part 8 of the series, Professor Tim Noakes outlines key moments in the development of hydration science between 1983 and the early 2000s. He discusses the first known example of exercise-associated hyponatremic encephalopathy and explains why misconceptions about how the human body regulates temperature and blood sodium concentrations during exercise led to the mismanagement of that case and many others. He notes that despite scientific discoveries regarding the causes and optimal treatment of EAHE, incidences of the condition were increasing in the U.S. military and among U.S. marathon runners. He proposes several explanations for this occurrence, first among them the promotion of the Zero-Percent Dehydration and Water as a Tactical Weapon Doctrines. What we have learned, he explains in conclusion, is that when scientific truth is “pitted against the power of modern marketing,” that truth “will not be heard.”

Read MoreThe Hyponatremia of Exercise, Part 8

Professor Tim Noakes highlights key moments in the evolution of official drinking guidelines from 1880 to 2007, focusing on various organizations’ departures from sound scientific practices in the 1980s and ‘90s. He reviews, in particular, the American College of Sports Medicine’s Position Stands of that era, as well as the U.S. military’s similar acceptance of the Zero-Percent Dehydration Doctrine despite the lack of scientific evidence supporting the associated drinking guidelines. As evidence of the danger of these recommendations mounted, the U.S. military began to revise its position. The sports drink industry, however, continued to overlook the risk of overhydration. As Noakes comments, “When commerce becomes involved in science, the rules of proper scientific conduct soon change.”

Read MoreThe Hyponatremia of Exercise, Part 7

Professor Tim Noakes explains how industry-supported research created what would prove to be a fatal fable about athletes’ hydration needs during exercise. Noakes calls this fable the “Zero-Percent Dehydration Doctrine,” which led to a dangerous prescription that athletes drink as much as they can tolerate during exercise, regardless of exercise intensity, personal characteristics, or environment. Noakes outlines the methodology behind a study by Drs. Scott Montain and Edward Coyle that was integral to the creation of this prescription and explains why the researchers’ conclusions were flawed. He elucidates how so-called experts helped the sports drink industry, with the assistance of the ACSM, by creating a disease out of dehydration that conveniently could be treated with the consumption of its products, sometimes to disastrous effects.

Read MoreThe Hyponatremia of Exercise, Part 6

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