It goes without saying that those of us who CrossFit are biased and consider CrossFit to be the premier fitness catalyst. We endure not only grueling, high-intensity workouts, but criticism from all other fitness disciplines as well. We stay protective and prideful of our box and our fellow members, and we continue on. We honor fallen warriors and correlate painful workouts with common female names. We sweat under the aphorism of “forging elite fitness.” But is CrossFit truly the elite fitness program? The science behind our programming suggests that this might be the case. Here is some of the science behind how CrossFit affects the body…Physiology of CrossFit.

Our skeletal muscle system is the primary mechanism that provides movement and force in our everyday lives. We utilize these muscles to walk, run, lift, sit, push, and pull. Inside our muscle groups are two primary types of muscle fibers: Type I and Type II. Type I muscle fibers are commonly referred to as “slow twitch” fibers, as they can go to full tension in about 110 milliseconds. Our Type II fibers can complete tension in less than half that time, around 50 milliseconds, and are thus considered to be our “fast twitch” fibers. Our Type II fibers can be further categorized into IIa and IIx fibers.

Image Credit: Graph courtesy of “Physiology of Sport and Exercise” 5th ed. W. Larry Kenney, PhD.

It is important to understand these fiber types by understanding how they produce force and how they are affected by exercise inflicted damage. . Since Type I fibers contract more slowly, they are primarily used on longer duration exercises, such as distance running and biking. Because they are not designed to endure large amounts of load, they do not hypertrophy (increase in size.) They do, however, continually adapt to process oxygen and energy consumption more efficiently. Type IIa and IIx fibers are designed to withstand load and exert force. Their design allows them to sustain heavier loads, but with less endurance. Type IIx, for example, is able to exert more force than IIa but at shorter duration. This is visualized in the chart, which shows the ratio of force to endurance. As the chart shows, the Type I fibers hold less force, but sustain that ability for an extended time. The Type II fibers can exert more force, but the endurance threshold drops more rapidly.

Now, think of the three major types of body structures in everyday fitness. From lean to large, they are: the distance runner, the CrossFitter, and the bodybuilder. This variation in body composition is due to the muscle fibers utilized in the everyday exercise routine for each regimen. Distance runners endure long runs that require extensive metabolic efficiency, and therefore activate primarily Type I fibers. Competitive bodybuilders rely on large loads to produce extreme size and definition, and therefore activate the Type II fibers for their ability to hypertrophy. Now look at a champion CrossFitter: lean muscle mass with functional ability in distance and endurance exercises as well as heavy load burdens.

The reason CrossFit is so effective is that it is programmed to activate and exercise all three types of muscle fibers. A standard 12-week programming cycle will consist of a combination of distance events, timed events, and Olympic lift events. Running and distance events work the Type I fibers and increase metabolic efficiency. Timed and round events work the Type IIa fibers by utilizing medium weight loads at a specific duration. Our performances of single Olympic lifts are working our Type IIx fibers, by lifting heavy loads for short durations.

Many of our military, Special Forces, fire, and rescue services utilize CrossFit as a lifestyle, not just a hobby. Some individuals prefer their own fitness programming to ours, and that is perfectly acceptable. CrossFit is for every body, but not everyone.

AlanAlan Fijalkowski is a US Marine Corps veteran of Iraq and Afghan war. Now he is a full time Firefighter and Paramedic for the Department of Defense in Colorado. He was introduced to CrossFit in 2005 and has been an avid fan since. He is also distance road racer (5K to Half Marathon) and a hobby mountain biker and skier.   Currently he holds an A.S. in Paramedicine and is a currently studying for a B.S. in Public Health, and is a father of two boys.  Follow Alan socially at Instagram: FijalkowskiAJ  Twitter: AlanFijalkowski   or at

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