Athletic Training and Sports Health Care

Original Research 

Association of Prior Injury With the Report of New Injuries Sustained During CrossFit Training

Laura A. Chachula, DO; Kenneth L. Cameron, PhD, MPH, ATC; Steven J. Svoboda, MD

Abstract

CrossFit training (CrossFit, Inc., Santa Cruz, CA) has increased in popularity in the past decade, along with associated injury. Although the effectiveness of CrossFit training is associated with its dynamic approach to eccentric exercise, which yields rapid physical improvements, few studies have been published regarding the safety of these training methods. The purpose of this study was to examine the characteristics of athletes engaged in CrossFit training and to determine if these characteristics were associated with injury prevalence after the initiation of training. Individuals reported injury history, CrossFit experience, and the presence of joint injuries sustained from CrossFit participation. A significant correlation was found between history of prior injury and an increased prevalence of new injury in individuals participating in CrossFit training. Individuals with a history of joint injury were 3.75 times as likely to sustain an injury during CrossFit training (P = .04; 95% confidence interval: 0.88, 18.6). Clinicians should be aware that patients with prior injuries may be more susceptible to injury during CrossFit workouts. [Athletic Training & Sports Health Care. 2016;8(1):28–34.]

Abstract

CrossFit training (CrossFit, Inc., Santa Cruz, CA) has increased in popularity in the past decade, along with associated injury. Although the effectiveness of CrossFit training is associated with its dynamic approach to eccentric exercise, which yields rapid physical improvements, few studies have been published regarding the safety of these training methods. The purpose of this study was to examine the characteristics of athletes engaged in CrossFit training and to determine if these characteristics were associated with injury prevalence after the initiation of training. Individuals reported injury history, CrossFit experience, and the presence of joint injuries sustained from CrossFit participation. A significant correlation was found between history of prior injury and an increased prevalence of new injury in individuals participating in CrossFit training. Individuals with a history of joint injury were 3.75 times as likely to sustain an injury during CrossFit training (P = .04; 95% confidence interval: 0.88, 18.6). Clinicians should be aware that patients with prior injuries may be more susceptible to injury during CrossFit workouts. [Athletic Training & Sports Health Care. 2016;8(1):28–34.]

Extreme conditioning programs include exercises that improve overall strength and aerobic fitness through repetitive, compound movements performed in high intensity cardiovascular sessions.1,2 Workouts are often performed in periods of time as short as 20 to 30 minutes and can be performed alone or with a group. Training regimens such as CrossFit (CrossFit, Inc., Santa Cruz, CA), Insanity, and P90X are among these programs and have gained popularity during the past several years.1 The benefits of these extreme conditioning programs include great gains in strength and endurance (eg, improved maximal oxygen uptake or consumption and work capacity) by forcing the body to adapt to a broad, evolving training regimen.2–4 Extreme conditioning program workouts are largely based on eccentric exercises often involving open chain movements where the joint is not restricted in space. Eccentric contractions, which involve the lengthening of a loaded muscle-tendon unit, can generate tremendous forces while using fewer motor units.5–7 However, when performed improperly or overzealously, these types of exercises can cause indirect musculoskeletal injury to include tendinopathies, ligamentous injury, and even rhabdomyolysis.1,6,7 Fatigue, weakness, and prior injury can increase risk for harm, especially when performing exercises that require great precision and skill.1,6 The safety of Extreme conditioning programs, and of CrossFit in particular, has thus been called into question.1,8–10

The purpose of this study was to examine the characteristics of participants engaged in CrossFit training, including prior injury history, CrossFit experience, and joint injuries sustained during CrossFit practice. A primary goal was to examine the association between these characteristics and the prevalence of new joint injuries reported since the initiation of CrossFit training. We hypothesized that a history of prior injury would be associated with new joint injuries incurred during CrossFit training.

Methods

Research Design

The protocol was approved by the local Institutional Review Board with U.S. Army Human Research Protection Office 2nd level approval. This is an original study of retrospective, cross-sectional design, implemented at one military installation at the United States Military Academy in West Point, New York.

Participants

Participants included individuals aged 17 to 50 years who voluntarily met throughout the week for group CrossFit workouts. Over a 6-week period, these athletes were solicited from one of two primary exercise facilities on one army post to take a one-time online survey. Informed consent was obtained from all participants agreeing to participate in the study and a link to a brief electronic survey was distributed via e-mail for participants to complete at their convenience within a 2-month time period. Fifty-four individuals completed the survey of 58 individuals who initiated it. Females comprised 25.9% (n = 14) of the group and males 74.1% (n = 40). Among the 54 study participants, ages were distributed into the following groups: 17 to 24 years (n = 28; 51.8%), 25 to 34 years (n = 14; 25.9%), and 35 to 50 years (n = 12; 22.2%).

Procedures

A single 20-question multiple-choice survey was distributed to study participants asking them to report their training and injury history before and after starting CrossFit workouts. For study purposes, injury was defined as the onset of harm to a joint, with new injury defined as the onset of harm to a joint sustained during CrossFit workouts. Baseline fitness levels were established by questioning the average weekly frequency of exercise or sport activity more than 30 minutes per day. CrossFit experience was addressed in terms of duration of practice (ie, how many months of consistent Cross-Fit participation) and perceived proficiency level, which was defined on a scale from 1 to 5 extending from novice to expert. Frequency (ie, how many CrossFit sessions per week) was also assessed and participants reported whether these sessions were led by CrossFit certified instructors. Participants were questioned about the location of any preexisting joint injury (eg, hip, knee, ankle, shoulder, elbow, wrist, or back) and whether symptoms improved or were made worse through participation in CrossFit training. Participants sustaining new injuries were asked whether this resulted in missed training days and if they sought medical attention.

Statistical Analysis

Descriptive statistics were calculated initially, including frequencies and percentages for categorical data and means and standard deviations for continuous variables. To examine the association between categorical variables, Pearson's chi-square or Fisher's exact test was used as appropriate. An alpha level of less than .05 was used for all statistical comparisons. All data were analyzed using STATA/SE version 10.1 (StataCorp, College Station, TX).

Results

Fifty-four surveys were completed of 58 surveys initiated, for a 93% response rate. Individuals reported the average number of times per week they exercised or played sports for at least 30 minutes at a time over the previous month (Table 1). Forty-three individuals (79.6%) reported exercising or playing sports five or more times per week for at least 30 minutes per day. The majority of study participants (n = 37; 68.5%) reported an average of three or more CrossFit workouts per week over the prior month (Table 2).

Self-Reported Average Weekly Bouts of Exercise/Sport for ≥ 30 Minutes Each

Table 1:

Self-Reported Average Weekly Bouts of Exercise/Sport for ≥ 30 Minutes Each

Self-Reported Average Weekly CrossFit Participation

Table 2:

Self-Reported Average Weekly CrossFit Participation

Experience with CrossFit training was addressed as duration of consistent participation in workouts. Nearly half of the group (n = 25; 46.3%) reported 12 or more months of experience (Table 3). The perceived level of expertise in CrossFit performance is shown in Table 4. Almost 60% of participants (n = 32; 59.2%) reported they mostly or always participated in sessions led by a certified trainer. This is displayed along with the distribution of the remaining 40% in Table 5. The majority (n = 30; 55%) of participants reported that their CrossFit participation was mostly with a small group of less than 10 participants (Table 6).

Self-Reported Duration of Consistent CrossFit Participation

Table 3:

Self-Reported Duration of Consistent CrossFit Participation

Perceived Level of Expertise Performing CrossFit Workouts

Table 4:

Perceived Level of Expertise Performing CrossFit Workouts

Frequency of Participation in Instructor-led CrossFit Workouts

Table 5:

Frequency of Participation in Instructor-led CrossFit Workouts

Typical CrossFit Practice Among Participants

Table 6:

Typical CrossFit Practice Among Participants

Participants reported history of any joint injury prior to starting the CrossFit program. Thirty-six (66.6%; 36 of 54) of all individuals reported prior injury to one or more joints. The distribution of these 101 joint injuries is shown in Table 7. Of all survey participants, 44% (24 of 54) reported a new injury occurring after starting their CrossFit regimen. Of the 36 participants who reported a history of injury prior to starting CrossFit, 55.6% (20 of 36) also reported a new injury (Figure 1). Using Fisher's exact test, we found that the relationship between a history of prior joint injury and new CrossFit injury was significant (P = .04). The odds ratio and Pearson's chi-square test revealed that individuals with a history of joint injury were 3.75 times as likely to sustain a new injury during CrossFit training (P = .04; 95% confidence interval: 0.88, 18.6). All 9 survey participants who reported that their injury prevented some period of participation in CrossFit training also had a history of prior joint injury; this finding was significant by Fisher's exact test (P = .04).

Distribution of Prior and New Injuries by Location

Table 7:

Distribution of Prior and New Injuries by Location

Distribution of new and prior injury.

Figure 1.

Distribution of new and prior injury.

Among the 24 participants reporting a new Cross-Fit-related injury, there was a total of 40 joint injuries reported (Table 7). Injuries occurred predominantly in the back (11 of 40; 27.5%) and shoulder (9 of 40; 22.5%). Participants with new or persistent joint pain reported that of the typical CrossFit exercises listed, back pain was aggravated most by dead lifts and kettle bell swings, knee pain was aggravated most by box jumps, and shoulder and elbow pain were both aggravated by ring dips (Figure 2).

Distribution of joint pain exacerbation with specific exercise.

Figure 2.

Distribution of joint pain exacerbation with specific exercise.

Injury prevalence was not associated with age (Figure 3) and CrossFit experience (Figure 4). Frequency of participation in CrossFit instructor-led sessions was also not significantly associated with injury (P = .07); however, injury prevalence was 66.6% (12 of 18) in individuals who reported they seldom or never trained with instructors and 38.7% (12 of 31) in those who reported they mostly or always did. Finally, all 6 participants seeking medical care for a new CrossFit-related injury also reported a history of prior joint injury before the initiation of CrossFit training; yet again this did not reach statistical significance (P = .08).

Injury prevalence by age.

Figure 3.

Injury prevalence by age.

Injury prevalence by CrossFit (CrossFit, Inc., Santa Cruz, CA) experience.

Figure 4.

Injury prevalence by CrossFit (CrossFit, Inc., Santa Cruz, CA) experience.

Discussion

The purpose of this study was to examine the characteristics of athletes engaged in CrossFit training and to determine whether these characteristics were associated with injury prevalence after the initiation of training. The current study reveals a significant correlation between history of prior joint injury and an increased prevalence of injury associated with Cross-Fit participation. Participants who reported a history of joint injury prior to initiating any CrossFit training were nearly four times as likely to sustain a subsequent injury during CrossFit workouts. Although there was an overall CrossFit injury prevalence of 44% (24 of 54) among study participants, those without prior injury had a prevalence of 22% (4 of 18) and those with a history of joint injury had a much higher prevalence of 55% (20 of 36). A history of joint injury was also significantly correlated with missed training sessions secondary to new joint injury.

The association between prior injury and an increased likelihood of subsequent joint injury during CrossFit training has not been reported in previous studies.4,9,10 Weisenthal et al. reported that most injuries sustained during CrossFit training occurred acutely without a history of prior injury (P < .001).10 They analyzed prior injury by specific body part, whereas we did not. For example, in our study an individual sustaining a knee injury during CrossFit workouts was still classified as having a history of prior injury even if that initial injury was to the hip. Recognizing the kinetic chain, we anticipated that injury to one joint might increase the susceptibility for subsequent injury in surrounding joints and did not limit our query to isolated joint reinjury. Further, prior studies on self-reported sports injury data show a greater recall bias when individuals were asked more details associated with an injury (only 61% reported 12-month injury history accurately) than when simply asked to report presence of injury (ie, yes or no).11

Although the findings of this study, suggesting an association between history of prior injury and subsequent joint injury, are new to CrossFit literature, this is an established relationship already in many sport and exercise studies.12–14 One such study followed 12 elite-level soccer teams over two consecutive seasons and found that players who were injured in one season had almost three times the risk of sustaining an injury in the following season.13 Players with a history of prior injury had an injury incidence of 87%, whereas those who did not had an incidence of 48%.13 Noting the potential for subsequent injury in CrossFit athletes with an injury history, these individuals should progress cautiously when reintroducing activity of this intensity to their fitness routine.

There is a wide range of injury prevalence (16% to 74%) associated with CrossFit training reported in studies.9,4,10 This study reports an injury prevalence of 44%. Despite the variation in these results among studies, there exists a general consensus on injury pattern. We report a predominance of new injury to the back and shoulder, which is supported in the current literature.9,10 These studies show that injury sustained from CrossFit training occurs most commonly with power lifting and gymnastics movements and are seen at a similar consistency as injuries in gymnasts (shoulder injuries) and Olympic and power lifters (shoulder and back injuries).9,10 Similarly, we noted individuals reporting aggravated shoulder and back pain with ring dips, kettle bell swings, and deadlift exercises—movements common to both gymnastics and weight lifting sports.

Our study additionally supports findings by Weisenthal et al.10 that there was no significance between age (P = .56) or experience (ie, length of participation in CrossFit; P = .99) with injury occurrence in CrossFit training. Their study did find a significant decline in injury rate with trainer presence (P = .028) that our study supports, but not with statistical significance. This lack of correlation may be due to an inadequately powered study. Regardless, participation in CrossFit workouts with an instructor present to lead or supervise is an important factor to consider when initiating this type of training. Certified trainers may help prevent subsequent new injury by ensuring adherence to proper form during workouts.

Whether CrossFit (and possibly all Extreme conditioning programs) inherently poses an increased risk of injury or whether the competitive atmosphere of these programs in group sessions discourages personal regulation of workouts is debatable.1 This is not to say that CrossFit training should be avoided, however. The safe practice of Extreme conditioning programs such as CrossFit has been demonstrated in military studies where it is integrated into a well-supervised, comprehensive training program.4,8 One study even saw a significant decline of 67% in the number of previous overuse injuries by eliminating overtraining.4 The prevention of overuse injuries by avoiding overtraining is supported in multiple studies and should also be considered when incorporating CrossFit workouts into a fitness regimen.15,16

Similar to other studies, this study has several limitations. We sampled participants from a highly selected population where some participants (ie, cadets, military enlisted personnel, and officers) are required to meet minimum fitness standards and have a paucity of medical problems. As such, findings of this study may understate what might be expected in the general population due to the relative extreme fitness levels of military athletes. Disparity in both age and gender also limit the study. Ages were distributed predominately into the 17 to 24 years age category (n = 28; 51.8%), likely due to increased Extreme conditioning program participation by young cadets. Gender disparity is also apparent and likely reflects the approximate distribution (85% male, 15% female) of cadets at the time of the study.

The survey did not assess how soon after initiation of the CrossFit training that joint injury occurred. This is important because a more experienced Cross-Fit participant reporting an injury from workouts may have sustained that injury when less experienced. This could have contributed to the lack of association between CrossFit experience and injury prevalence. Additionally, we did not survey laterality of injury. Although this did not affect the injury prevalence, the numbers of new and prior injuries among participants may be misrepresentative (eg, if multiple participants had bilateral knee injuries). Response options when questioned about exercises affecting joint pain were also limited to common CrossFit exercises (kipping, kettle bell swings, dead lifts, ring dips, and box jumps) and may not be representative of typical CrossFit workouts, which by definition are prone to variability.

Study weaknesses inherent to cross-sectional self-reporting studies include the identification of participants and a self-selection bias. Workouts were not guided by study protocol in any way and participants may not have adhered to the CrossFit training principles. We did not identify or exclude potential rogue participants. Finally, a self-selection bias exists because participants were given the option of survey completion. It is not unreasonable that individuals having sustained a prior injury would have been more likely to participate to report these injuries.

Implications for Clinical Practice

Because individuals who have sustained prior injuries are more predisposed to injury during CrossFit participation, clinicians should maintain heightened awareness when dealing with this subgroup. Those individuals electing to participate in CrossFit work-outs should be counseled on knowing their training limits and possible risks of reinjury that may occur. Appropriate and thorough rehabilitation of prior injuries should also be completed prior to engaging in CrossFit training.

Conclusion

This study is one of a few to report the athlete characteristics, injury prevalence, and patterns associated with CrossFit training. We found that individuals with prior joint injury had a 3.75 times increased likelihood of sustaining a CrossFit-related injury and were more likely to miss training sessions due to injury. Although the advantage of providing a total body workout in a short period of time is appealing, the findings observed are concerning. Further research is necessary to determine whether the type, severity, and rehabilitation of joint injuries prior to participating in CrossFit training affect injury prevalence sustained during CrossFit training.

References

  1. Bergeron MF, Nindl BC, Deuster PA, et al. Consortium for Health and Military Performance and American College of Sports Medicine consensus paper on extreme conditioning programs in military personnel. Curr Sports Med Rep. 2011;10:383–389. doi:10.1249/JSR.0b013e318237bf8a [CrossRef]
  2. Glassman G. Foundations. CrossFit Journal (online serial). 2002;1. Available at: http://journal.crossfit.com/2002/04/foundations.tpl.
  3. Pain J, Uptgraft J, Wylie R. CrossFit study. Comm Gen Staff College. 2010:1–34.
  4. Smith MM, Sommer AJ, Starkoff BE, Devor ST. Crossfit-based high intensity power training improves maximal aerobic fitness and body composition. J Strength Cond Res. 2013;27:3159–3172. doi:10.1519/JSC.0b013e318289e59f [CrossRef]
  5. Rees JD, Wolman RL, Wilson A. Eccentric exercises: why do they work, what are the problems and how can we improve them?Br J Sports Med. 2009;43:242–246. doi:10.1136/bjsm.2008.052910 [CrossRef]
  6. Sassmannshausen G. The older athlete. In: Johnson DL, Mair SD, eds. Clinical Sports Medicine. Philadelphia: Elsevier Health Sciences; 2006:91–96.
  7. Svoboda S, Taylor D. Muscle injuries. In: Johnson DL, Mair SD, eds. Clinical Sports Medicine. Philadelphia: Elsevier Health Sciences; 2006:117–128.
  8. Grier T, Canham-Chervak M, McNulty V, Jones BH. Extreme conditioning programs and injury risk in a US Army Brigade Combat Team. US Army Med Dep J. 2013;Oct–Dec:36–47.
  9. Hak PT, Hodzovic E, Hickey B. The nature and prevalence of injury during CrossFit training [published online ahead of print November 22, 2013]. J Strength Cond Res.
  10. Weisenthal BM, Beck CA, Maloney MD, DeHaven KE, Giordano BD. Injury rate and patterns among CrossFit athletes. Orthop J Sports Med. 2014;2:2325967114531177. doi:10.1177/2325967114531177 [CrossRef]
  11. Gabbe BJ, Finch CF, Bennell KL, Wajswelner H. How valid is a self reported 12 month sports injury history?Br J Sports Med. 2003;37:545–547. doi:10.1136/bjsm.37.6.545 [CrossRef]
  12. Cameron KL, Mountcastle SB, Nelson BJ, et al. History of shoulder instability and subsequent injury during four years of follow-up. J Bone Joint Surg Am. 2013;95:439–445. doi:10.2106/JBJS.L.00252 [CrossRef]
  13. Hägglund M, Waldén M, Ekstrand J. Previous injury as a risk factor for injury in elite football: a prospective study over two consecutive seasons. Br J Sports Med. 2006;40:767–772. doi:10.1136/bjsm.2006.026609 [CrossRef]
  14. Kucera KL, Marshall SW, Kirkendall DT, Marchak PM, Garrett WE Jr, . Injury history as a risk factor for incident injury in youth soccer. Br J Sports Med. 2005;39:462. doi:10.1136/bjsm.2004.013672 [CrossRef]
  15. Bullock SH, Jones BH, Gilchrist J, Marshall SW. Prevention of physical training-related injuries: recommendations for the military and other active populations based on expedited systematic reviews. Am J Prev Med. 2010;38(1 suppl):S156–S181. doi:10.1016/j.amepre.2009.10.023 [CrossRef]
  16. Walker TB, Lennemann LM, Anderson V, Lyons W, Zupan MF. Adaptations to a new physical training program in the combat controller training pipeline. J Spec Oper Med. 2011;11:37–44.

Self-Reported Average Weekly Bouts of Exercise/Sport for ≥ 30 Minutes Each

TIMES PER WEEKNO.%
Never00
< 100
100
223.7
323.7
4712.9
52037
61324
71018.5

Self-Reported Average Weekly CrossFit Participation

DURATION (WEEKS)NO.%
< 111.8
1 to 21629.6
3 to 53564.8
6 to 1123.7

Self-Reported Duration of Consistent CrossFit Participation

LEVELNO.%
< 147.4
1 to 21120.4
3 to 559.3
6 to 11916.7
≥ 122546.3

Perceived Level of Expertise Performing CrossFit Workouts

LEVELNO.%
1 (novice)47.4
2611
32139
4611
5 (expert)1731.5

Frequency of Participation in Instructor-led CrossFit Workouts

PARTICIPATIONNO.%
Don't know35.6
Never814.8
Sometimes1120.4
Mostly1629.6
Always1629.6

Typical CrossFit Practice Among Participants

CROSSFIT PRACTICENO.%
Alone713
With partner1222
Small group (< 10)3055.6
Large group (> 10)59.3

Distribution of Prior and New Injuries by Location

INJURY LOCATIONPRIOR INJURIES REPORTEDPARTICIPANTS REPORTING THAT PAIN FROM PRIOR INJURY WAS AT SAME OR GREATER LEVEL ON STARTING CROSSFITNEW INJURIES SUSTAINED SINCE STARTING CROSSFIT
Low back18 (17.8%)711 (27.5%)
Shoulder17 (16.8%)59 (22.5%)
Elbow8 (7.9%)34 (10%)
Wrist9 (8.9%)54 (10%)
Knee22 (21.8%)75 (12.5%)
Ankle18 (17.8%)74 (10%)
Hip9 (8.9%)53 (7.5%)
Total1013940
Authors

From Tripler Army Medical Center, Graduate Medical Education, Tripler AMC, Hawaii (LAC); and the Department of Orthopaedic Surgery, Keller Army Hospital, West Point, New York (KLC, SJS).

The authors have no financial or proprietary interest in the materials presented herein.

The views and opinions expressed in this manuscript are those of the authors and do not reflect the official policy of the Department of the Army, the Department of Defense, or the United States Government.

Correspondence: Laura A. Chachula, DO, Tripler Army Medical Center, Graduate Medical Education, 1 Jarrett White Road, Tripler AMC, HI 96859. E-mail: laura.a.chachula.mil@mail.mil

Received: May 05, 2015
Accepted: September 29, 2015

10.3928/19425864-20151119-02

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