The Science of Why I Don’t Do CrossFit: A Follow-Up

Posted: September 1, 2014 in General Posts
Tags: , , , , ,

I received quite a bit of feedback, both good and bad, on my last commentary on CrossFit. Some things I discussed with people one on one, some people trolled the page, and some people actually learned something new! However, there still seem to be some misunderstandings and misconceptions that I want to clear up. I have put together a list of some of the most common arguments, statements, and comments that I received on my position on CrossFit and I address them below.

But first, I’d like to quote Dr. Kenneth Jay, who received similar feedback from Crossfitters to some of his articles. His words of wisdom: “No emotional attachment.” As he reminds us, “[B]e willing to abandon your opinion—because in science, you are not entitled to your own opinion; you are only entitled to what you can argue for.”

Finally, my education levels and experience were called into question by numerous Crossfitters. Let me clarify: I have a Bachelor of Science and a Master of Science in Biology. I worked for the Department of Defense in a physiological laboratory for a military experimental unit. I am second author on a paper published in the Journal of Applied Physiology dealing with exercise performance, physiological responses to stressors, heart rate, VO2/VO2 max, and diving physiology. I am currently working on my Ph.D. in an integrated exercise physiology and sports nutrition program at Texas A&M. In addition to my own collegiate athletics career as a student athlete, I am starting my third year as a volunteer assistant coach for multi-year national championship track and field teams at A&M. I work with athletes in strength development, conditioning, rehabilitation, and event-specific training. I not only work with top-level athletes, but also with top-level, world-renowned coaches, doctors, and training staff. I know that I don’t know everything. I have a lifetime of learning ahead of me. But I’ve also been in great positions to absorb the knowledge of people who have already spent their lifetime dedicated to becoming experts in their respective fields. I’ve been able to read, discuss, assimilate, and synthesize their knowledge of exercise physiology, proper training techniques, injury prevention, injury rehabilitation, workout periodization, workout progressions, athletic training, and much more.

So without further ado, I address some common issues people had with my article:

It’s better than people doing nothing. Aren’t you happy to have them off the couch?

I love that CrossFit gets people excited about fitness. I love that it fosters a community of people working out together and motivating each other. Does that change my opinion about its programming (or lack thereof)? Absolutely not. The benefits of getting people off the couch are outweighed by the stress that is being put on their bodies. The potential for injury in CrossFit is drastically increased when newbies jump into it, especially if their coach’s certification and knowledge is questionable.

Let’s say there is an overweight person sitting on a couch. When they are sitting on that couch, they have lots of options they can take to improve their situation. If they jump into CrossFit and sustain an injury that puts them back on the couch, the options they have are now limited. For some people who have experienced extreme injuries like rhabdomyalysis or stroke, their lives may be drastically changed and they may never be able to exercise again. These are obviously extreme examples, but the concept is applicable to any degree of injury. There are far safer and more efficient ways to get people off the couch and work them into routines that will better target their goals than a cookie-cutter WOD at extremely high intensity.

I saw so much improvement from doing CrossFit. It changed my life!

Of course you did. If you go from doing nothing to doing something, you’re going to see results. Studies have shown that untrained individuals show favorable responses to nearly any protocol implemented, and their gains are often at a very high rate (6, 8, 12). You could have achieved this result from nearly any exercise program. Why did CrossFit work so well for you, then, when you didn’t personally see results from anything else you tried? The answer is found in the community aspect of CrossFit: you were accountable to someone, you had fellow sufferers, you had a community with which to compare your numbers and times.

The conclusion from this phenomenon, then, is that any benefits that you notice from CrossFit as a novice that you did not perceive in other training regimens is purely social and derived from a greater commitment to your exercise program. In the absence of that social factor, science tells you that initial physiological responses are essentially the same for any training program of choice (14). So why not apply that same commitment to one that is tailored to your needs and goals, while keeping safety a priority?

My gym is different. My coaches teach proper form and stop me if I’m doing it wrong. My gym has an intro program everyone has to go through before they can do the WODs. If you haven’t trained at my gym, you can’t comment. 

I can, because CrossFit has a very distinct style of training to which most gyms adhere. If you’re doing CrossFit then you’re doing the WOD’s, which are posted on the main CrossFit website each day, or something very close to it. I can make the generalization because CrossFit has key similarities in its workouts that make up its fundamental flaws: lift many times, lift quickly, don’t rest, keep going until you can’t anymore. This is totally encompassed in the CrossFit term, AMRAP: as many reps as possible.

While this may not be an issue for a minute or two of push-ups or pull-ups, it becomes a big deal when it’s Olympic or Power lifts. Why? Because, as Kraemer et al. (12) state, “total-body exercises such as the power snatch and power clean have been regarded as the most effective exercises for increasing muscle power because they require fast force production to successfully complete each repetition”. This means that these exercises require a great deal of force on each rep in order to perform them correctly, which cannot be maintained for high volume sets such as those listed below:

Example WODs (from 2014 CrossFit Games qualifying rounds):

WOD 1: Complete as many reps as possible in 8 minutes of (Men/Women):

135/95-lb. deadlifts, 10 reps

15 box jumps, 24/20-inch

185/135-lb. deadlifts, 15 reps

15 box jumps, 24/20-inch

225/155-lb. deadlifts, 20 reps

15 box jumps, 24/20-inch

275/185-lb. deadlifts, 25 reps

15 box jumps, 24/ 20-inch

315/205-lb. deadlifts, 30 reps

15 box jumps, 24/20-inch

365/225-lb. deadlifts, 35 reps

15 box jumps, 24/20-inch

WOD 2: 60 clean and jerks (135 / 95 lb.). Time Cap: 7 minutes

Workouts like those listed above are asking the body to try to hit peak force for more repetitions than what the physiology of the body allows. For example, Chiu et al. (5) found that subjects exhibited decreased movement velocity, decreased peak force, and decreased rate of force development after just four sets of five repetitions of speed squats. If your rate of force and peak force decrease after just 20 reps of speed squats, with rest intervals, how can you expect to maintain fast force production over 30, 40, or 60 consecutive snatches or cleans?

Another study by Skurvydas et al. (21) showed greater low frequency fatigue and subsequent reduction in optimal positions in subjects performing 100 drop jumps compared to 50 drop jumps, concluding that greater magnitude of exercises causes a deterioration in form and increase in muscle fatigue. Which means that if you’re doing the WOD, or anything like it, you are putting excessive stress on your body via sub-optimal form, accumulating fatigue effects, and lack of planned recovery time. While each individual is different due to genetics, such a workout scheme over time will cause the body to break down. The question, then, is not will it have an effect on your body, but rather how long will it take to have an effect on your body? You may bully your body through a battle or two, but it is a war you will ultimately lose.

People just need to be smart about how they do the CrossFit workouts. People should evaluate their gym and their coaches and make sure they know what they’re talking about.

When you have people who have perhaps not worked out their entire lives or who have been casual gym-goers, you can’t assume that they know the right questions to ask, the right way to warm up, how to recognize signs of fatigue, when their form has deteriorated, or the smart time to stop the workout. A good training method recognizes this and ensures that its instructors are adequately trained to educate their members on these subjects and assist them with applying these subjects to their training. A good training method meets people where they are and helps them get where they need to be without throwing them immediately into the deep end. Studies have shown that trying to do too much too quickly leads to fatigue and overtraining because the body is not able to physiologically adapt to the stress (4). The result is typically extreme soreness and/or injury (14).

Any good training method should be concerned with injury prevention and take measures to ensure that participants are properly evaluated before performing workouts to determine whether or not they are ready for the intensity of the prescribed workout. Any good training method should allow flexibility for those who have not yet adapted or adjusted. A good training method does not assume the participant knows proper progression. Successful training programs are dependent on program design, proper instruction, setting goals, evaluation, correct exercise prescription, and progression aimed at individual-specific goals (12). The general principles of progression are purposeful variation, specificity, and the gradual increase of stress during training, so that demands on the neuromuscular system are progressively increased and not immediately shocked and shot (12, 14).

Two predominant types of overtraining in resistance exercise are too high intensity and too high volume (15), which are both integral parts of CrossFit. Thus, there is no smart or safe way to do a CrossFit workout except to drastically alter it, in which case it’s technically not CrossFit. Classic CrossFit training is fundamentally wrong according to current scientific standards and methodology in the field of strength and conditioning. I have a really big problem with the above statements and the way that the CrossFit culture seeks to push all responsibility onto the individual members. They charge the average person with trying to find a good coach, asking the right questions about certifications, evaluating the workouts, evaluating themselves and their level of fitness, and evaluating the level of safety of workouts and boxes. Due to the multitude of information and misinformation in the fitness world, these are unreasonable expectations to have of the general public when their health is on the line.

There are good and bad coaches in every sport, not just CrossFit.

Well of course. I don’t deny that at all. But the “fad” aspect of CrossFit has allowed it to grow too quickly and has made it easy for beginners to start coaching beginners. The biggest barrier to entry into the CF world is not time or training, but money. I’m not saying there aren’t bad personal trainers, but a personal trainer is likely not teaching you to Olympic or power lift with large amounts of weight and/or for speed.

Kraemer et al. (12) points out that these lifts “require additional time for learning and proper technique is essential.” The exercises and workouts that CrossFit employs drastically increases the danger that comes with having a bad coach. The importance of having a qualified and knowledgeable coach is summed up by Pearson, et al. (14), who point out that “(t)he effectiveness of any training program is defined by the ability of the strength and conditioning specialist to effectively use scientific principles as the basis for making a multitude of decisions on a day-to-day basis as to the individual progression of a resistance-training program for an athlete.”

I understand that some coaches and boxes are better than others, but it should be a corporation-wide requirement with oversight that does not currently exist. CrossFit, Inc., in an effort to evade liability and allow “free market function”, has essentially said that this task is neither their problem nor their responsibility and that they will play no role in quality control. Instead, founder Greg Glassman has been quoted as saying, “Crossfit can kill you” as well as stating, “We have a therapy for injuries at CrossFit called STFU (shut the f*** up)”.

Such blatant disregard for the safety and well-being of Crossfitters is wholly inexcusable! Why let your body take the beating of being a cash-cow to a pyramid business scheme that ultimately does not have your best interest in mind? Why allow yourself to be taken advantage of in order to benefit others? The point to exercise and athletics is to achieve health, fitness, and performance; therefore any properly developed training program should be 100% based on a concern and care for the individual and should be carried out with a mindset of selfless service.

At the end of the day, it is the workouts that I am ultimately concerned with: lack of personalization, lack of programming, lack of progression, too high reps, too little rest, and a focus on speed of completing exercises rather than quality of the exercise. These types of workouts, coupled with the probability of a coach with a weekend certificate, make CrossFit particularly dangerous.

All sports and athletic activities have a risk of injury. CrossFit isn’t any different. So should we not play football or run either?

It does not mean that at all. Of course there is risk of injury in each sport, and even in the world of general fitness. However, you cannot compare apples and oranges by comparing CrossFit to athletics. In order to compare injury risks, you would have to compare the injury rates in the strength and conditioning training for those sports. Athletes in sports such as football or track spend time in the weight room and on the track or field practicing and training in order to prevent injury during their actual performance and cause neuromuscular adaptations. Strength training in athletic programs specifically targets weaknesses that lead to injury and underperformance. The difference is that CrossFit tries to make a sport out of this training, instead of viewing it as a method of injury prevention. By making strength and conditioning training into a competition of how many lifts you can do or how fast you can do them, CrossFit compromises these training goals and instead makes the participant susceptible to injury.

Additionally, athletes recognize the risk that comes with competing in their sport at a very high level. These people aren’t just trying to get “fit” by competing, they are trying to be in the top percentile of their sport and many times they are trying to earn their living by doing so. Are there very high rates of injury among football players? Absolutely. But I’m not taking an average person off the couch or out of the local gym and putting them in pads and sending them out into a game to get them in shape. I’m not going to grab a mom of three and put her in a track meet to run sprints or hurdles to get her to lose some baby weight. But CrossFit takes these people and puts them into high intensity programs with complex lifts and high reps of auxiliary exercises, whereas elite athletes develop over years and years of building on past progress while being guided by highly trained professionals. That’s the difference.

You said you can’t use weights to increase cardiovascular performance, but it gets my heart rate up so it has to help my VO2/VO2 Max!

In my first article I quoted a comment made by Dr. Kenneth Jay, a Danish neurophysiologist (I apologize, my first article said he was Dutch, which was incorrect; find his bio here), regarding lifting weights for cardio. He details his points further in the following posts on his website, Fast Force First (Part 1Part 2).

Essentially, yes you can get your heart rate up using weights. However, increasing your heart rate does not correlate directly to increasing your VO2 or VO2 max (3). If this was the case, Dr. Jay says he could “scare you into shape”! Lifting weights fast does not result in the same training effect as typical cardiovascular exercises such as running, cycling, or rowing. Pearson et al. (14) outline this concept as well, stating “resistance-training programs do not typically improve maximal oxygen consumption to the extent that other modes of cardiovascular training do”. In fact, it is possible to have detrimental effects from spending too much time under tension, such as during high volume weight training. Dr. Jay explains that, over time, the excessive contraction of the thoracic Vena Cava not only leads to a lower VO2 but can also result in the thickening of the heart wall and a higher resting heart rate. To quote Dr. Jay, “This is NOT healthy!”

You have no scientific evidence on which to base your opinion.

Quite the contrary. Just because there are few papers that address the specific term, “CrossFit”, does not mean that scientific evidence for the detrimental effects of CF doesn’t exist. When you break it down to the fundamentals of CrossFit, you see that the style of workout goes against basic principles of exercise physiology that have been around for decades. Few papers have addressed CrossFit specifically for two reasons: (1) it is relatively new and it takes time to put studies together and get them published, and (2) physiologists likely don’t see a need academically to specifically address CrossFit because there is already a great deal of work showing that the fundamentals of the workouts utilized by CF are detrimental and not ideal for proper training, especially for athletes.

Here are some basic training principles that are ignored or violated by CrossFit WODs and training methods:


As Pearson et al. (14) state, “The essence of periodization is the variation in load, volume, rest periods, and exercises done in a consistent manner over time.” Many studies have supported the concept that systematic variation of volume and intensity is the most effective training protocol, and that periodized programs result in greater changes in strength, motor performance, total body weight, lean body mass, and percent body fat than non-periodized programs (6, 11, 12, 22). There is a need for variation in volume and intensity to increase fitness and minimize fatigue (4, 12). Fatigue after-effects are cumulative, so that stressful training without sufficient recovery results in systemic fatigue effects, especially in the immune system (4). Classic CrossFit does not periodize or strategically vary workouts, and does not trade off between volume and intensity.

Progression, Programming, and Individualization

The body must be given “appropriate” stressors in order for the neuromuscular system to adapt (3). What is “appropriate” varies for each individual, so that maximizing the effectiveness of a strength training program requires its individualization after performing a health screening and needs analysis. This analysis should include health/injury concerns, appropriate frequency, muscle group strengths and weaknesses, etc. (12). Proper resistance training involves the manipulation of variables both throughout each workout and over time, including: muscle actions, resistance, volume, exercises, workout structure, sequence of exercises, rest intervals, repetition velocity, and frequency of training (12). There is also an inverse relationship between volume and intensity, and it is better to use higher volumes at the start of a training plan and gradually modify (4, 12). It is also recommended that multiple joint exercises, such as snatch, clean, and push press, be performed early in a training session when fatigue is minimal (12). Classic CrossFit does not follow proper programming during workouts, implement progression over time, and does little to modify for individual needs, goals, or weaknesses.

Multiple Sets

With a goal of maximizing strength development, multiple sets per muscle group have been found to be superior to single sets (10, 11, 16, 20, 23, 24). During the first 6-12 training sessions (or 10 weeks), an individual may benefit from single-sets but multiple-sets are significantly superior thereafter. Additionally, no studies have shown single set protocols to be superior for trained or untrained individuals (6, 8, 12, 14). Greater magnitudes of exercises, which are common when performing single sets, have also been found to result in slower muscle strength recovery, taking 7 or more days after exercise to return to normal strength levels (21). CrossFit, however, utilizes single set protocols for multiple WODs, such as the popular “Isabel” as well as the workouts listed previously in this article. Such workouts do not allow for muscle recovery during or following the workout.

Rest Intervals

The ability to sustain consistent repetitions over consecutive sets in weight training is dependent on the length of rest interval, which must be long enough to recover ATP (energy) and clear fatiguing substances (H+) so that force production can be restored and maximum strength development is enabled (2, 9, 17, 19, 23, 24). Greater strength increases have been showing utilizing longer rest periods of 2-5 minutes as compared to 30, 60, and 90 seconds (12, 15, 18). The American College of Sports Medicine (1) especially stresses the need for rest periods in multiple joint lifts (i.e., snatch, clean, push press), for which 3-5 minute rest intervals are recommended. CrossFit does not implement specified rest times and often discourages resting by prescribing workouts that encourage as many reps as possible in a given amount of time, or by requiring lifts and ancillary exercises be completed in as little time as possible.

Training and Recovery of the Neuromuscular System and Avoiding Overtraining

While these concepts go along with periodization and programming, they are more specific to the neuromuscular system. Periods of reduced volume are necessary for neuromuscular system to recover and to avoid overtraining muscles (14). Following exercise, the body experiences both fitness and fatigue effects, each to varying degrees depending on the type of workout performed. Fitness effects following training allows for improvement and up-regulation of peripheral and central nervous systems; fatigue after effects are both neural (down-regulation of nervous system) and metabolic (depletion of energy sources – ATP) (4, 13). The fatigue effect accumulates over time, and as it increases, the adaptive ability of the individual decreases, resulting in overtraining (4). So what causes such a fatigue effect? According to Pearson et al. (14), too much volume for too long of a duration is one of the key factors in overtraining. CrossFit requires a large volume of lifts and exercises be done on a consistent basis, with no planned period for recovery. High intensity and high volume are staples of classic CrossFit, and both are scientifically shown to result in overtraining (14).

In conclusion, there has been much scientific work that addresses the fundamental flaws and resultant safety issues associated with CrossFit. From lack of individualization to overtraining, there is a scientific basis for the argument against CrossFit and its random, “one size fits all” methodology. Exercise physiology is a complex topic to which I hope I have brought some clarity for the readers of my initial article. My goal here isn’t to inflame people; my goal is to educate and to have a conversation about something that many people may not want to talk about. Many people don’t know the risks associated with CrossFit, and I want people to be able to make an educated decision. Ultimately, though, it is each person’s decision to make, and if the person accepts the risks and the stress that his/her body will have to endure, then that is the individual’s choice. I love that CrossFit has been able to forge a cohesive community that is excited about working out, however, we have to make sure that our desire to be a part of something does not overcome our powers of reasoned thought.


**I thank and acknowledge my fellow graduate student, Phillip Scruggs, for his help in assimilating papers, facilitating discussion, and providing helpful edits during my writing process.




 1. American College of Sports Medicine. Position stand: progression models in resistance training for healthy adults. Medicine and Science in Sports and Exercise. 34: 364–380, 2002.

2. Baechle, T.R., Earle, R.W., Wathen, D. Resistance train Essentials of Strength Training and Conditioning. T.R. Baechie and R.W. Earle, eds. Champaign, IL: Human Kinetics. 395-425, 2000.

3. Brooks, G.A., Fahey, T.D., Baldwin, K.M. Exercise Physiology: Human Bioenergetics and its Applications (4th edition). New York, NY: McGraw-Hill, 2005.

4. Chiu, L.Z.F., Barnes, J.L. The Fitness-Fatigue Model Revisited: Implications for Planning Short- and Long-Term Training. Journal of Strength and Conditioning. 25(6):42-51. 2003.

5. Chiu, L.Z.F., Fry, A.C., Schilling B.K., Johnson, E.J., Weiss, L.W. Neuromuscular Fatigue and Potentiation Following Two Successive High Intensity Resistance Exercise Sessions. European Journal of Applied Physiology. 92: 385-392. 2004.

6. Fleck, S.J. Periodized Strength Training: A Critical Review. Journal of Strength and Conditioning Research. 13(1): 82-89. 1999.

7. Fry, A.C., Webber, J.M., Weiss, L.W., Fry, M.D., Li, Y. Impaired Performances with Excessive High Intensity Free-Weight Training. Journal of Strength and Conditioning Research. 14(1): 54-61. 2000.

8. Hakkinen, K. Factors influencing trainability of muscular strength during short term and prolonged training. National Strength and Conditioning Association Journal. 7:32–34. 1985.

9. Harris, R.C., Edwards, R.H., Hultman, E., Nordesjo, L,O., Nylind, B., Sahlin, K. The time course of phosphocreatine resynthesis during the recovery of quadriceps muscle in man. Pflugers Arch. 97:392-397. 1976.

10. Kraemer, W.J. A series of studies-the physiological basis for strength training in American football: fact over philosophy. Journal of Strength and Conditioning Research. 11:131–142. 1997.

11. Kraemer, W.J., Ratamess, N.A., Fry, A.C., Triplett-McBride, T., Koziris, L.P., Bauer, J.A., Lynch, J.M., Fleck, S.J. Influence of resistance training volume and periodization on physiological and performance adaptations in college women tennis players. American Journal of Sports Medicine. 28:626–633. 2000.

12. Kraemer, W.J., Ratamess, N.A. Fundamentals of Resistance Training: Progression and Exercise Prescription. Medicine and Science in Sports and Exercise. 36(4):674-688. 2004.

13. Noakes, T, A St Clair Gibson, and E Lambert. “From catastrophe to complexity: a novel model of integrative central neural regulation of effort and fatigue during exercise in humans: summary and conclusions.”British Journal of Sports Medicine39: 120-24.

14. Pearson, D, Faigenbaum, A, Conley, M, Kraemer, W.J. The National Strength and Conditioning Association’s Basic Guidelines for the Resistance Training of Athletes. Journal of Strength and Conditioning Research. 25(6): 42-51. 2000.

15. Pincivero, D.M., Lephart, S.M., Karunakara, G. Effects of rest interval on isokinetic strength and functional performance after short term high intensity training. British Journal of Sports Medicine. 31:229–234. 1997.

16. Rhea, M.R., Alvar, B.A., Ball, S.D., Burkett, N. Three sets of weight training superior to 1 set with equal intensity for eliciting strength. Journal of Strength and Conditioning Research. 16:525–529. 2002.

17. Richmond, S.R., Godard, M.P. The effects of rest periods between sets to failure using the bench press in recreationally trained men. Journal of Strength and Conditioning Research. 18:846-849. 2004.

18. Robinson, J. M., Stone, M. H., Johnson, R. L., Penland, C. M., Warren, B. J., Lewis, D. Effects of different weight training exercise/rest intervals on strength, power, and high intensity exercise endurance. Journal of Strength and Conditioning Research. 9:216–221. 1995.

19. Sahlin, K., Ren, J.M. Relationship of contraction capacity to metabolic changes during recovery from a fatiguing contraction. Journal of Applied Physiology. 67:648-654. 1989.

20. Schlumberger, A., Stec, J., Schmidtbleicher, Single- vs. multiple-set strength training in women. Journal of Strength and Conditioning Research. 15:284–289. 2001.

21. Skurvydas A, Brazaitis M, Venckūnas T, Kamandulis S. Predictive value of strength loss as an indicator of muscle damage across multiple drop jumps. Applied Physiology, Nutrition, and Metabolism. 36(3):353-360, 2011.

22. Stone, M.H., O’Bryant, H., Garhammer, A Hypothetical model for strength training. Journal of Sports Medicine. 21:342-351. 1981.

23. Willardson, J.M. A Brief Review: Factors Affecting the Length of the Rest Interval Between Resistance Exercise Sets. Journal of Strength and Conditioning Research. 20(4): 978-984.

24. Willardson, J.M., Burkett, L.N. The Effect of Different Rest Intervals Between Sets on Volume Components and Strength Gains. Journal of Strength and Conditioning Research. 22(1):146-152. 2008.

  1. Christopher Beck says:

    Very nice article Erin.

    First of all, best of luck in getting your Ph.D. You are well on your way, so I have no doubt that you will complete this very successfully.

    Second, you are one of the very few people that I listen to since once I studied your background/dedication, it was very clear that you knew what you were talking about.

    Congratulations, and continued success.