• Evidence-Based Physical Training: Do CrossFit or P90X Make the Cut
    There is no denying the growing popularity of high-intensity circuit training programs (e.g., CrossFit™, P90X™, etc.). As a result, these high-intensity circuit training programs have attracted a lot of recent attention. Learn about their application to military fitness. From the NSCA TSAC Report.
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  • CrossFit GroupLooking at CrossFit and P90X
    There is no denying the growing popularity of high-intensity circuit training programs (e.g., CrossFit™, P90X™, etc.) (2,15,16).

    With the emphasis of such programs on hard exercise and short rest intervals in a highly competitive environment, it is not surprising such programs have become increasingly attractive to military populations.

    For example, over 58 non-profit military CrossFit affiliates now exist, including installations such as the Pentagon, the United States Military Academy, Fort Bragg, Fort Meade, and Luke Air Force Base (17).

    The rapid incorporation of these training techniques into military fitness programs has led to concerns about the safety and effectiveness of these programs, elsewhere referred collectively as extreme conditioning programs (ECPs)(3). Anecdotal reports of improved fitness test scores resulting from participation in ECPs have been countered by similar reports of serious injury and even lawsuits associated with the use of ECPs (14,16).

    Because increased rates of injury would have negative impacts on military readiness, it is important to assess ECPs from an evidence-based perspective, in order to determine whether or not ECPs enhance, or produce a detriment to, military “fit to fight” capacity.

    There do not appear to be any studies of ECPs in the peer-reviewed literature. A CrossFit affiliate group at Fort Hood conducted a study in 2009, but this work remains unpublished.

    Looking at CrossFit
    One non-peer-reviewed study on CrossFit was published in 2010 by the U.S. Army Command and General Staff College (17). The study subjects were 14 students of the College, and “were a mix of men and women with varying levels of physical fitness and CrossFit experience.”

    The study was eight weeks in duration, and the subjects performed an initial assessment of the Army Physical Fitness Test (APFT), plus three CrossFit workouts. After the training intervention, the subjects were post-tested on the same pre-assessments.

    The 2010 CrossFit study suffers from several deficiencies.

    The sample size was small; there was no control group, and no comparative group which trained utilizing protocols that have been demonstrated to improve military fitness (7,8,10,11,12). Laboratory measures of aerobic fitness/strength/power were not conducted.

    Differences in “average power” were the outcome variables used to assess performance improvements. The post-test results were reported as percentiles, and not tested statistically to determine if the differences were significant. For the APFT, post-test improvements of 7.33% and 4.77% were reported for the push-up and sit-up components. Some subjects recorded declines in performance on both tests. The 2-mi run was not assessed post-training due to inclement weather.

    Looking at P90X
    Another recent study which appeared in a non-peer-reviewed online journal examined the P90X ECP (23).

    This study evaluated the energy cost and exercise intensity of four different P90X workouts. The study utilized 16 subjects (9 men and 7 women). Pre-test assessments consisted of a treadmill test to measure maximal oxygen consumption (VO2max) and maximal heart rate. The subjects practiced each of the four P90X workouts selected for the study prior to the testing period.

    Heart rates (HR) were recorded at 1 min intervals, and used to calculate predicted VO2 and energy expenditure for each workout. The results predicted an average HR max of 67–83% for males, and 65–88% for females. Average VO2max values were 45–70% for males, and 45–80% for females. Average calculated calorie expenditure was 10.5–16.2 kcals/min for males, and 7.2–12.7 kcals/min for females.

    The authors concluded the four P90X workouts met American College of Sports Medicine (ACSM) recommendations for energy expenditure and exercise intensity, and represented an alternative option for exercisers looking to improve aerobic fitness and/or lose weight (23).

    Looking at the Studies Under a Microscope
    This P90X study suffers from some of the same design issues as the CrossFit study; small sample size, no control group, and no alternative intervention to compare the results (1,13).

    An additional problem is that HRs measured during discontinuous exercise appeared to be higher than those recorded during steady-state exercise, even when matched for VO2 (5,6). Therefore, VO2/energy consumption values calculated from HRs collected from circuit training protocols, like those in this study, could overestimate actual VO2/energy cost (5,6,21,22).

    In fact, recent evidence suggests discontinuous training protocols and steady-state aerobic exercise are very difficult to compare, when different rates/type of fuels used during exercise/recovery are considered (5,6,21). One study which directly measured energy cost during circuit weight training found lower absolute average expenditures of 9.0 kcal/min and 6.1 kcal/min (22). Measurements of VO2 from other circuit training studies suggest these protocols may not produce increases in training intensity sufficient to improve cardiorespiratory fitness, though the energy cost of such exercise may be beneficial for weight control (5,6).

    An additional concern with ECPs is the risk of injury; as these programs do not typically follow progressive exercise models recommended by organizations such as the National Strength and Conditioning Association (NSCA) and the ACSM (18,20). Injury incidences from ECPs are unknown beyond isolated case reports of exertional rhabdomyolysis (ERM) and delayed onset muscle soreness (DOMS) (3,19).

    Exertional rhabdomyolysis is frequently caused by excessive, vigorous exercise, and by untrained/low-fit individuals who “ramp up” the frequency/intensity of training too quickly (9). A recent review of ERM in the U.S. Army found annual rates of 7–8 per 10,000, a rate 300–400% higher than the estimated rate in the U.S civilian population (9). Those at greatest risk for ERM are soldiers with a record of previous heat injury, male, younger, African American, less-educated, and shorter lengths of military service. It is unknown to what extent ECPs may contribute to these high ERM rates.

    Addressing the Concerns
    A related concern is whether or not ECP trainer certification protocols are sufficiently rigorous to meet nationally recognized standards of quality, such as those established by the National Commission for Certifying Agencies (NCCA). According to its mission statement, the NCCA “helps to ensure the health, welfare and safety of the public through the accreditation of a variety of individual certification programs that assess professional competency,” (4).

    The NCCA utilizes a peer-review process to ensure the goal of its mission statement is met. Listings of NCCA accredited certification programs are available on the NCCA homepage. For example, the NSCA and the ACSM certification programs are NCCA accredited. At the present time, no ECP program has achieved NCCA accreditation.

    In summary, though ECPs such as CrossFit and P90X are very popular, this popularity does not appear to be warranted. There is little evidence from peer-reviewed studies that ECPs are safe and/or effective, particularly when compared to established training programs documented to improve military task performance. Though much more research needs to be conducted, ECPs do not seem, at this time, to represent training programs likely to improve military readiness.

    * The views expressed in this article are those of the author, and do not necessarily reflect the official position or policy of the Air Force, the Department of Defense, or the U.S. Government.
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    About the Author:

    Guy Leahy, Med, CSCS,*D

    Guy Leahy, Med, CSCS,*D is currently serving dual roles as the interim flight commander/exercise physiologist at Davis-Monthan Air Force Base in Tucson, AZ. Leahy is a member of the ACSM (American College of Sports Medicine), NSCA and is CSCS® certified. Leahy is the author/co-author of over 30 professional articles, including original research which has appeared in publications such as the Journal of Strength and Conditioning Research, TSAC Report, Medicine and Science in Sports and Exercise, Nature, Science, and Scientific American. He has presented at several conferences, most recently at the 2011 NSCA Annual Meeting, where he was also an invited speaker at the TSAC Special Interest Group. Leahy holds a Master of Education degree from Western Washington University and a Bachelor of Science degree from the University of Oregon.

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  • Disclaimer: The National Strength and Conditioning Association (NSCA) encourages the exchange of diverse opinions. The ideas, comments, and materials presented herein do not necessarily reflect the NSCA’s official position on an issue. The NSCA assumes no responsibility for any statements made by authors, whether as fact, opinion, or otherwise. 
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      Comment Posted by Member:

      Guy,

      You’ve made both inaccurate and misleading statements in your article. Allow me to correct a few.

      1. "There do not appear to be any studies of ECPs in the peer-reviewed literature.”

      This is false. The NSCA publishedmore» a peer-reviewed study of CrossFit under the title "Crossfit-based high intensity power training improves maximal aerobic fitness and body composition”

      The problem is the study’s own coordinator claims the injury data is completely fabricated. The investigation into this study, as well as the entire transcript of my interview with the author can be found here: http://journal.crossfit.com/2013/05/acsm.tpl

      The NSCA has failed to respond to this issue, perhaps you can help.

      2. You also criticize CrossFit for failing “...to meet nationally recognized standards of quality”, and for not “...achieving NCCA accreditation”.

      What you fail to note here is that CrossFit’s L1 Trainer Course is accredited by ANSI, making it the only *internationally* accredited fitness program in the world. We have no yet “achieved” the NCCA accreditation because we aren’t interested in it.

      3. You state that " though ECPs such as CrossFit...are very popular, this popularity does not appear to be warranted. There is little evidence from peer-reviewed studies that ECPs are safe and/or effective...”

      To suggest, in particular, that military men and women base their decisions to use CrossFit on peer-reviewed literature is laughable. On the contrary, our warriors on the ground decide if a program works based on observable, real-world results. This is why I chose to use CrossFit while serving in a combat unit 8 years ago. For examples of these types of results, one only need to look at the athletes competing in the CrossFit Games.

      I look forward to your response on these points.

      Thanks«less

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