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.

The Gastrointestinal System: Anatomy of Taste

The tongue has roughly 10,000 taste buds, with receptor types specific to each of the five basic tastes regionally distributed. Taste buds also exist elsewhere. Chemoreceptors in the nose and sinuses help sommeliers, cicerones, and gourmands assess taste more fully. And although we associate taste with deriving pleasure from the foods we eat, it also has a more fundamental biological function: survival.

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Lung Anatomy and Physiology: Asthma


Asthma is a chronic inflammatory disease of the airway. During an asthma attack, the respiratory tract becomes narrowed. This may be a survival mechanism — a reduction in airflow to limit lung injury from harmful airborne materials — that has gone awry in some individuals. Lon Kilgore, Ph.D., explains what happens to the body’s respiratory system during an asthma attack and why coaches must become cognizant of how to safeguard athletes in the case of an episode.

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The Lungs: Gas Exchange


Through breathing and gas exchange, our bodies manage to get oxygen into the blood and carbon dioxide out of the blood. How this is accomplished is conceptually simple but also exquisitely intricate and complex when considered in detail. Lon Kilgore, Ph.D., explains.

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Lung Anatomy: The Airway and Alveoli

The lungs are less like balloons and more like giant warm marshmallows. They contain 1,000 miles of air-conducting tubes. The surface area of the tiny air sacs that make up the lungs is roughly the size of a tennis court. Here, Lon Kilgore, Ph.D., describes the anatomy of the lungs and explains how the respiratory system works to move oxygen from the atmosphere into the bloodstream.

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Anatomy of the Lungs

As a key part of the respiratory system, the lungs help process a critical element of life and exercise: oxygen. The circulatory system then helps distribute oxygen throughout the body. To maintain this elegant system of supply and demand during sustained aerobic exercise, our ventilation rate increases by about 300 to 400%. If we push our exercise intensity, that rate can exceed baseline by more than 500%.

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The Heart, Part 9: Blood


Blood is made up of a solution of water and mineral ions and bioactive molecules called plasma. The solid portion of blood is made of cells, platelets, cell fragments, and very large molecules. The ratio of these two components, solid and liquid, is expressed as a percentage and is called the hematocrit. A higher hematocrit is associated with better endurance performance, but efforts to artificially elevate hematocrit can sometimes prove fatal.

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