Injury profile in CrossFit practitioners: systematic review

Fábio Hech Dominski Thais Cristina Siqueira Thiago Teixeira Serafim Alexandro Andrade About the authors

RESUMO

O CrossFit se apresenta como um novo método de treinamento físico que vem ganhando popularidade desde sua criação. O objetivo deste estudo foi analisar o perfil de lesões em praticantes de CrossFit por meio de uma revisão sistemática da literatura. Utilizaram-se as recomendações da Declaração PRISMA para condução da revisão sistemática. A busca foi realizada nas bases de dados CINAHL, SciELO, Science Direct, SCOPUS, LILACS, PEDro, PubMed, SPORTDiscus e Web of Science. Avaliou-se a qualidade metodológica dos estudos, entre os quais dez foram considerados elegíveis. A prevalência de lesões nos praticantes de CrossFit variou de 5 a 73,5%, e a taxa de lesão variou de 1,94 a 3,1 lesões a cada 1.000 horas de treinamento. A região corporal mais acometida por lesões nos estudos selecionados foram os ombros, seguidos pelas costas e joelhos. Em relação aos fatores associados às lesões, destacou-se o tipo de exercício realizado e o tempo de prática de CrossFit. O sexo apresentou associação com a prevalência de lesões, estudos demonstraram que os homens apresentaram maior número de lesões em relação às mulheres. A idade esteve entre os fatores que não estiveram associados às lesões. Conclui-se que os ombros são a região corporal mais comumente acometida entre os praticantes de CrossFit, em indivíduos do sexo masculino e com lesões prévias, muitas vezes obtidas em outras modalidades. Ainda, que o CrossFit pode ser praticado com segurança por indivíduos de 18 a 69 anos.

Descritores:
Exercício; Treinamento Intervalado de Alta Intensidade; Ferimentos e Lesões; Revisão.

RESUMEN

CrossFit es un nuevo método de entrenamiento físico y ha ganado popularidad desde su creación. El objetivo de este estudio fue analizar el perfil de lesiones en practicantes de CrossFit a través de una revisión sistemática. La Declaración PRISMA fue utilizada para la preparación de esta revisión. Se realizó una búsqueda bibliográfica en las siguientes bases de datos: CINAHL, SciELO, Science Direct, SCOPUS, LILACS, PEDro, PubMed, SPORTDiscus y Web of Science. Se evaluó la calidad metodológica de los estudios, entre los cuales diez estudios fueron considerados elegibles. La prevalencia de lesiones en los practicantes de CrossFit tuvo una variación del 5 al 73,5%, y la tasa de lesiones de 1,94 a 3,1 lesiones a cada 1000 horas de entrenamiento. La región corporal más lesionada fueran los hombros, seguido por las espaldas y rodillas. En relación a los factores asociados a las lesiones, se destacan el tipo de ejercicio fue realizado y el tiempo de práctica del CrossFit. En relación al género, los hombres presentaron más lesiones. La edad no estuvo asociada a las lesiones. Se concluye que la región corporal más comúnmente acometida entre los practicantes de CrossFit fueron los hombros, en individuos masculinos y con lesiones previas, muchas veces obtenidas en otras modalidades. Además, el CrossFit puede ser practicado con seguridad por individuos de 18 a 69 años.

Palabras clave:
Ejercicio; Entrenamiento de Intervalos de Alta Intensidad; Heridas y Lesiones; Revisión.

ABSTRACT

CrossFit is a new form of physical training that has become popular since its inception. This study aimed to analyze the injury profile of CrossFit practitioners through a systematic review. PRISMA recommendations were applied to this systematic review. Electronic search was performed in the databases CINAHL, SciELO, Science Direct, SCOPUS, LILACS, PEDro, PubMed, SPORTDiscus and Web of Science. The methodological quality of the studies was assessed. Ten studies were selected. The prevalence of injuries in CrossFit practitioners ranged from 5 to 73.5%, and the overall injury incidence rate per 1000 training hours ranged from 1.94 to 3.1 injuries. The body region most affected by injuries was the shoulders, followed by the back and the knees. Regarding associated factors, the type of exercise performed and CrossFit training time were related to injuries. Besides that, sex was associated to the prevalence of injuries, with men showing more injuries than women. Age was not related to injury prevalence. It was concluded that the most commonly affected body region among CrossFit practitioners was the shoulders, predominantly in males and with previous injuries, often obtained in other modalities. In addition, CrossFit can be safely practiced by individuals aged 18-69.

Keywords:
Exercise; High-Intensity Interval Training; Wounds and Injuries; Review

INTRODUCTION

It is noteworthy that there is a fairly recent interest of researchers and the general public in physical activities in which high intensity is prevalent11. Gillen JB, Gibala MJ. Is high-intensity interval training a time-efficient exercise strategy to improve health and fitness? Appl Physiol Nutr Metab. 2013;39(3):409-12. doi: 10.1139/apnm-2013-0187
https://doi.org/10.1139/apnm-2013-0187...
. Studies show that high intensity training provides more benefits to physical fitness and health while having shorter duration, when compared to traditional training methods11. Gillen JB, Gibala MJ. Is high-intensity interval training a time-efficient exercise strategy to improve health and fitness? Appl Physiol Nutr Metab. 2013;39(3):409-12. doi: 10.1139/apnm-2013-0187
https://doi.org/10.1139/apnm-2013-0187...
), (22. Skelly LE, Andrews PC, Gillen JB, Martin BJ, Percival ME, Gibala MJ. High-intensity interval exercise induces 24-h energy expenditure similar to traditional endurance exercise despite reduced time commitment. Appl Physiol Nutr Metab. 2014;39(7):845-8. doi: 10.1139/apnm-2013-0562.
https://doi.org/10.1139/apnm-2013-0562...
.

Thus, CrossFit presents itself as a new method of physical training that has gained popularity since its creation and implementation at the beginning of the new millennium33. Moran S, Booker H, Staines J, Williams S. Rates and risk factors of injury in CrossFit: a prospective cohort study. J Sports Med Phys Fitness. 2017;57(9):1147-53. doi: 10.23736/S0022-4707.16.06827-4
https://doi.org/10.23736/S0022-4707.16.0...
. It aims to promote physical fitness through the development of components such as aerobic capacity, muscular strength and endurance, speed, coordination, agility and balance44. Lichtenstein MB, Jensen TT. Exercise addiction in CrossFit: Prevalence and psychometric properties of the Exercise Addiction Inventory. Addict Behav Rep. 2016;3:33-7. doi: 0.1016/j.abrep.2016.02.002, through sports and functional exercises, comprising weightlifting exercises, gymnastic and aerobic conditioning movements, which can be executed at high intensity55. Tibana RA, de Farias DL, Nascimento D, Da Silva-Grigoletto ME, Prestes J. Relação da força muscular com o desempenho no levantamento olímpico em praticantes de CrossFit(r). Rev Andal Med Deporte 2018;11:84-8. doi: 10.1016/j.ramd.2015.11.005
https://doi.org/10.1016/j.ramd.2015.11.0...
.

In the world, there are about 12,000 certified and registered fitness centers and gyms that offer CrossFit33. Moran S, Booker H, Staines J, Williams S. Rates and risk factors of injury in CrossFit: a prospective cohort study. J Sports Med Phys Fitness. 2017;57(9):1147-53. doi: 10.23736/S0022-4707.16.06827-4
https://doi.org/10.23736/S0022-4707.16.0...
; of these, approximately 440 are in Brazil, involving approximately 40,000 practitioners and athletes66. Sprey JW, Ferreira T, Lima MV, Duarte Jr A, Jorge PB, Santili C. An epidemiological profile of CrossFit athletes in Brazil. Orthop J Sports Med. 2016;4(8):2325967116663706. doi: 10.1177/2325967116663706
https://doi.org/10.1177/2325967116663706...
. Research shows a significant growth in the number of practitioners of this modality in various populations, such as healthy or obese individuals and athletes, due to its challenging and motivational nature77. Heinrich KM, Patel PM, O'Neal JL, Heinrich BS. High-intensity compared to moderate-intensity training for exercise initiation, enjoyment, adherence, and intentions: an intervention study. BMC Public Health. 2014;14(1):789. doi: 10.1186/1471-2458-14-789
https://doi.org/10.1186/1471-2458-14-789...
)- (99. Sibley BA, Bergman SM. What keeps athletes in the gym? Goals, psychological needs, and motivation of CrossFit(tm) participants. Int J Sport Exerc Psychol. 2017:1-20. doi: 10.1080/1612197X.2017.1280835
https://doi.org/10.1080/1612197X.2017.12...
. Evidence shows that about 5% of CrossFit practitioners present a dependency relationship, which is significantly associated with the incidence/frequency of injuries44. Lichtenstein MB, Jensen TT. Exercise addiction in CrossFit: Prevalence and psychometric properties of the Exercise Addiction Inventory. Addict Behav Rep. 2016;3:33-7. doi: 0.1016/j.abrep.2016.02.002.

The American College of Sports Medicine (ACSM) suggests potential benefits of CrossFit, but also highlights significant injury risks in extreme conditioning programs like the aforementioned1010. Bergeron MF, Nindl BC, Deuster PA, Baumgartner N, Kane SF, Kraemer WJ, 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(6):383-9. doi: 10.1249/JSR.0b013e318237bf8a
https://doi.org/10.1249/JSR.0b013e318237...
. These programs involve the execution of some exercises that, if performed incorrectly or excessively, can cause musculoskeletal injuries, ligament injuries, and even rhabdomyolysis1010. Bergeron MF, Nindl BC, Deuster PA, Baumgartner N, Kane SF, Kraemer WJ, 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(6):383-9. doi: 10.1249/JSR.0b013e318237bf8a
https://doi.org/10.1249/JSR.0b013e318237...
. In this way, concerns over the potential injury risk associated with the intense and repetitive nature of CrossFit and the necessary technical requirements for performing the exercises safely have grown in academia and in the practice of modality1111. Eather N, Morgan PJ, Lubans DR. Improving health-related fitness in adolescents: the CrossFit teens(tm) randomised controlled trial. J Sports Sci. 2016;34(3):209-23. doi: 10.1080/02640414.2015.1045925
https://doi.org/10.1080/02640414.2015.10...
.

Gathering information from studies available in the literature on injuries of CrossFit practitioners allows us to get to know data related to the prevalence and rates of injury by hours of training, most commonly injured body regions, and injury-related factors, aiming to develop and implement preventive actions in its practice, considering the increase of the number of practitioners and, consequently, of environments that allow for the practice of CrossFit. In addition, a systematic review with analysis of these aspects for clinical decision making in the fields of medicine and physical therapy is valuable. Since the currently published reviews on CrossFit injuries1212. Klimek C, Ashbeck C, Brook AJ, Durall C. Are injuries more common with CrossFit training than other forms of exercise? J Sport Rehabil. 2017;1-17. doi: 10.1123/jsr.2016-0040
https://doi.org/10.1123/jsr.2016-0040...
), (1313. Meyer J, Morrison J, Zuniga J. The benefits and risks of CrossFit: a systematic review. Workplace Health Saf. 2017; 65(12):612-618. doi: 10.1177/2165079916685568
https://doi.org/10.1177/2165079916685568...
were limited to investigating the injury rate by comparing it with other types of physical exercises and sports, no studies were found addressing the various aspects these injuries have, such as rate and prevalence, commonly affected body regions and related factors, hence resulting in an injury profile14,15. Thus, the objective of this study was to analyze the injury profile of CrossFit practitioners through a systematic review of the literature.

METHODOLOGY

This is a systematic review of the literature following the recommended criteria of the PRISMA Statement - Preferred Reporting Items for Systematic Reviews and Meta-Analyses1616. Moher D, Shamseer L, Clarke M, Ghersi D, Liberati A, Petticrew M, et al. Preferred reporting items for systematic review and meta-analysis protocols (PRISMA-P) 2015 statement. Systematic Rev. 2015;4(1):1. doi: 10.1186/2046-4053-4-1
https://doi.org/10.1186/2046-4053-4-1...
.

Search Strategy

Representing a significant part of global scientific production, the search for studies was performed on the electronic databases related to Sport and Physical Exercise Sciences, and Physical Therapy: CINAHL via EBSCO, SciELO (Scientific Electronic Library Online), Science Direct, SCOPUS (Elsevier), LILACS (Literatura Latino-Americana e do Caribe em Ciências da Saúde), PEDro (Physiotherapy Evidence Database), PubMed (National Library of Medicine and National Institutes of Health), SPORTDiscus via EBSCO, and Web of Science - Coleção Principal (Thomson Reuters Scientific).

The search took place in May 2017 and ended on 11 May of the same year. In order to include all production conducted on the topic in the databases selected, and because of the recent creation and development of CrossFit, the only term used for article search was “Crossfit”, in the same way the study by Meyer et al.13 was conducted.

The search in the database Web of Science was performed in Core Collection, the basic search field with the term “Crossfit”, the item Topic selected and Timespan set as all years.

ELIGIBILITY CRITERIA

Only original articles about injuries with athletes and practitioners of CrossFit were considered, including studies with quantitative, qualitative or mixed approach, with summaries and texts available in full online until 11 May 2017. No time limit was set. Review articles, case studies, conference abstracts, editorials and letters were excluded.

Eligibility of the studies occurred by means of the PICOS criteria and are detailed in Table 1.

Table 1
Criteria for inclusion and exclusion of the studies selected for review

Selection of studies and data extraction

The studies were selected by three reviewers (FHD, TCS, TTS), independently. Initially, analysis of the article titles identified through the search strategy was conducted, followed by examination of the abstracts. Subsequently, analysis of the full text of the articles selected in the previous steps was performed. Disagreements between reviewers were resolved by consensus.

For determining injury profile in CrossFit, data analysis was conducted while considering the following categories: prevalence and type of injury, body region affected by injury, injury rate by training time and whether factors were related to injuries or not.

Assessment of the methodological quality of the studies

In order to assess the methodological quality of the studies, the recommendations of STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) were followed, by means of the STROBE Statement - Checklist of items that should be included in reports of cross-sectional studies1717. Vandenbroucke JP, von Elm E, Altman DG, Gotzsche PC, Mulrow CD, Pocock, SJ, et al. Strengthening the reporting of observational studies in epidemiology (STROBE): explanation and elaboration. Epidemiology. 2007;18(6):805-35. doi: 10.1097/EDE.0b013e3181577511
https://doi.org/10.1097/EDE.0b013e318157...
), (1818. Von Elm E, Altman DG, Egger M, Pocock SJ, Gotzsche PC, Vandenbroucke JP, et al. The strengthening the reporting of observational studies in epidemiology (STROBE) statement: guidelines for reporting observational studies. Int J Surgery, 12(12):1495-9. doi: 10.1136/bmj.39335.541782.AD
https://doi.org/10.1136/bmj.39335.541782...
. This checklist has 22 items that received a score from 0 (does not meet) to 1 (meets), the total score was obtained from the sum of the item scores and, according to the final score of the study, a classification in accordance with Mataratzis et al. (1919. Mataratzis PSR, Accioly E, Padilha PC. Deficiências de micronutrientes em crianças e adolescentes com anemia falciforme: uma revisão sistemática. Rev Bras Hematol Hemoter. 2010;32(3):247-256. doi: 10.1590/S1516-84842010005000078
https://doi.org/10.1590/S1516-8484201000...
was defined: a) when the study met more than 80% of the criteria as established by STROBE, indicating better quality of studies; b) - when 50% to 80% of STROBE criteria were met; and c) when less than 50% of the criteria were met.

RESULTS

The search resulted in 684 entries. After duplicate exclusion (n=75) and title reading, 100 articles were selected for the abstract. In this step, other 79 were excluded 79, with 21 left for full reading. Finally, 10 studies were part of the final review (Figure 1).

Figure 1
Flowchart of the selection process of the studies included

The sample size of the selected studies ranged from 34 to 1,393, totaling 3,307 research subjects, 2,244 being of male and 871 of female sex (192 subjects did not have their sex reported). The subjects were characterized as CrossFit practitioners in six studies, athletes in three studies, and soldiers in one. The average age of the research subjects ranged from 26.8 to 38.9 years, and the age group ranged from 18 to 69 years.

The prevalence of injuries in the studies ranged from 5 to 73.5%. The rate of injuries every 1,000 hours of CrossFit training ranged from 1.94 to 3.1 injuries (Chart 1).

Chart 1
CrossFit injuries: Author, sample and main results related to injuries

Figure 2
Body regions affected by injuries in studies on CrossFit (number of studies per regions)

The body region most affected by injuries in the studies selected were the shoulders (7 studies). Back and knees were injured regions in practitioners of 4 studies each, followed by the lumbar region in 3 studies, and arms/elbows in 2 studies. Body regions like head/neck, wrists, thighs, legs and feet were cited as injured regions in one study (Figure 2).

Several injury-related factors were observed in CrossFit practitioners and athletes. The most present factors within the studies were the type of exercise performed, in 5 studies33. Moran S, Booker H, Staines J, Williams S. Rates and risk factors of injury in CrossFit: a prospective cohort study. J Sports Med Phys Fitness. 2017;57(9):1147-53. doi: 10.23736/S0022-4707.16.06827-4
https://doi.org/10.23736/S0022-4707.16.0...
), (2222. Weisenthal BM, Beck CA, Maloney MD, DeHaven KE, Giordano BD. Injury rate and patterns among CrossFit athletes. Orthop J Sports Med. 2014;2(4):2325967114531177. doi: 10.1177/2325967114531177
https://doi.org/10.1177/2325967114531177...
)- (2525. Summitt RJ, Cotton RA, Kays AC, Slaven EJ. Shoulder injuries in individuals who participate in CrossFit training. Sports Health. 2016;8(6):541-6. doi: 10.1177/1941738116666073
https://doi.org/10.1177/1941738116666073...
, and the training time of CrossFit, in 3 studies66. Sprey JW, Ferreira T, Lima MV, Duarte Jr A, Jorge PB, Santili C. An epidemiological profile of CrossFit athletes in Brazil. Orthop J Sports Med. 2016;4(8):2325967116663706. doi: 10.1177/2325967116663706
https://doi.org/10.1177/2325967116663706...
), (2626. Aune KT, Powers JM. Injuries in an extreme conditioning program. Sports Health. 2017;9(1):52-8. doi: 10.1177/1941738116674895
https://doi.org/10.1177/1941738116674895...
), (2727. Montalvo AM, Shaefer H, Rodriguez B, Li T, Epnere K, Myer GD. Retrospective injury epidemiology and risk factors for injury in CrossFit. J Sports Sci Med. 2017;16(1):53.. In addition, sex presented relation to the prevalence of injuries, where men presented a higher number of injuries in relation to women, and the presence of prior injury was associated with new injuries. In 5 studies, age was among the factors not associated with injuries (Chart 2).

Chart 2
Results of studies on CrossFit in relation to factors associated and not associated with injuries

Regarding to the assessment of methodological quality according to the criteria of STROBE, adherence to the criteria varied between 50% and 81.8%, the majority of studies being classified as B and only one study classified as A, having above 80% of the criteria met (Table 2).

Table 2
Assessment of methodological quality of the studies included

DISCUSSION

This study aimed to analyze the injury profile of CrossFit practitioners through a systematic review of the literature. For determining injury profile in CrossFit, data such as prevalence and type of injury, body region affected, injury rate by training time, and whether factors were related to injuries or not like sex, age and type of exercise were analyzed and will be further discussed in the following sections.

Injury prevalence

The prevalence of injuries was distributed unevenly among studies, which can be explained by the large amplitude in sample sizes, aside from differences between the populations analyzed and training characteristics.

Although one of the studies showed high prevalence of injuries with 73.5%2121. Hak PT, Hodzovic E, Hickey B. The nature and prevalence of injury during CrossFit training. J Strength Cond Res. 2013. doi: 10.1519/JSC.0000000000000318
https://doi.org/10.1519/JSC.000000000000...
, this one was conducted through questionnaire available in online forums, which is a methodological limitation, as it is not known how many individuals have seen the research and opted not to respond. In addition, Hak et al. (2121. Hak PT, Hodzovic E, Hickey B. The nature and prevalence of injury during CrossFit training. J Strength Cond Res. 2013. doi: 10.1519/JSC.0000000000000318
https://doi.org/10.1519/JSC.000000000000...
conducted the study with practitioners of all CrossFit participation levels; on the other hand, the prior training experience, that is, the previous practice of the participants of the research by Weisenthal et al. (2222. Weisenthal BM, Beck CA, Maloney MD, DeHaven KE, Giordano BD. Injury rate and patterns among CrossFit athletes. Orthop J Sports Med. 2014;2(4):2325967114531177. doi: 10.1177/2325967114531177
https://doi.org/10.1177/2325967114531177...
and Grier et al. (2020. 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. 2013:36-47. may have contributed to the lower prevalence of injuries when compared to the study by Hak et al. (2121. Hak PT, Hodzovic E, Hickey B. The nature and prevalence of injury during CrossFit training. J Strength Cond Res. 2013. doi: 10.1519/JSC.0000000000000318
https://doi.org/10.1519/JSC.000000000000...
, but this relationship is not clear in the literature yet.

Injury rate

When compared to other modalities of physical exercise or sport, the injury rate of CrossFit is not considered high. A rate of 3.1 injuries every 1,000 hours of training as a maximum value found in the studies was observed2121. Hak PT, Hodzovic E, Hickey B. The nature and prevalence of injury during CrossFit training. J Strength Cond Res. 2013. doi: 10.1519/JSC.0000000000000318
https://doi.org/10.1519/JSC.000000000000...
. In sports, rates from 2.3 to 33 injuries in running, 2.5 in handball, 5.4 in triathlon, 5.45 in gymnastics, 9.6 in soccer and 26.7 in rugby, every 1,000 hours of training, were found2828. Korkia P, Tunstall-Pedoe D, Maffulli N. An epidemiological investigation of training and injury patterns in British triathletes. Br J Sports Med. 1994;28(3):191-6.)- (3333. Videbaek S, Bueno AM, Nielsen RO, Rasmussen S. Incidence of running-related injuries per 1000 h of running in different types of runners: a systematic review and meta-analysis. Sports Med. 2015;45(7):1017-26. doi: 10.1007/s40279-015-0333-8
https://doi.org/10.1007/s40279-015-0333-...
.

It is inferred that this result may occur due to the absence of determinants such as physical contact and practice of exercise on irregular soils, which were already shown to be associated with injuries in sports3434. Woods C, Hawkins R, Hulse M, Hodson A. The Football Association Medical Research Programme: an audit of injuries in professional football: an analysis of ankle sprains. Br J Sports Med. 2003;37(3):233-8. doi: 10.1136/bjsm.37.3.233
https://doi.org/10.1136/bjsm.37.3.233...
)- (3636. Bahr R, Karlsen R, Lian O, Ovrebo RV. Incidence and mechanisms of acute ankle inversion injuries in volleyball: a retrospective cohort study. Am J Sports Med 1994;22(5):595-600. doi: 10.1177/036354659402200505
https://doi.org/10.1177/0363546594022005...
.

Associated factors

A higher injury rate was observed in males, a result that may be related to the lower demand of men for trainers compared to women with the aim of being supervised. Evidence shows that women consult their trainers for doubts and supervision more when compared to men2222. Weisenthal BM, Beck CA, Maloney MD, DeHaven KE, Giordano BD. Injury rate and patterns among CrossFit athletes. Orthop J Sports Med. 2014;2(4):2325967114531177. doi: 10.1177/2325967114531177
https://doi.org/10.1177/2325967114531177...
. Publications on injuries comparing men and women have also shown a higher prevalence in males, in sports such as basketball, judo and running3737. Almeida Neto AFD, Tonin JP, Navega MT. Characterization of sport injuries in the basketball. Fisioter Mov. 2013;26(2):361-8. doi: 10.1590/S0103-51502013000200013
https://doi.org/10.1590/S0103-5150201300...
)- (3939. Manzato ALG, Camargo HP, Graças D, Martinez PF, Oliveira Júnior SA. Lesões musculoesqueléticas em praticantes de judô. Fisioter Pesqui. 24(2):127-34. doi:10.1590/1809-2950/16325024022017.
https://doi.org/10.1590/1809-2950/163250...
.

Several populations have sought to practice CrossFit, many already practicing other forms of physical exercise or sport and, in some cases, this population is composed of people with prior injuries. It was observed that this is an important related factor, because individuals with previous injuries are 3.75 times more likely to acquire them again in CrossFit2323. Chachula LA, Cameron KL, Svoboda SJ. Association of prior injury with the report of new injuries sustained during CrossFit training. Athletic Training Sports Health Care. 2016;8(1):28-34. doi:10.3928/19425864-20151119-02
https://doi.org/10.3928/19425864-2015111...
, specifically with regard to the shoulder, where it was shown that athletes with prior injury are eight times more likely to injure the shoulder compared to athletes with healthy shoulders2626. Aune KT, Powers JM. Injuries in an extreme conditioning program. Sports Health. 2017;9(1):52-8. doi: 10.1177/1941738116674895
https://doi.org/10.1177/1941738116674895...
. Therefore, the need for attention to the anamnesis of new practitioners in sites that offer CrossFit practice is highlighted, in order to know prior injuries and prevent the recurrence of these injuries.

The association between injury and training time was shown to be not clear, as some studies have shown that practitioners with longer training time suffer more injuries in relation to those with less time66. Sprey JW, Ferreira T, Lima MV, Duarte Jr A, Jorge PB, Santili C. An epidemiological profile of CrossFit athletes in Brazil. Orthop J Sports Med. 2016;4(8):2325967116663706. doi: 10.1177/2325967116663706
https://doi.org/10.1177/2325967116663706...
), (2727. Montalvo AM, Shaefer H, Rodriguez B, Li T, Epnere K, Myer GD. Retrospective injury epidemiology and risk factors for injury in CrossFit. J Sports Sci Med. 2017;16(1):53.. On the other hand, a study found an incidence rate of injury among athletes with less than six months of experience to be 2.5 times greater than that of athletes with more than six months of experience, which can be explained by the lack of execution of the correct movements technique2626. Aune KT, Powers JM. Injuries in an extreme conditioning program. Sports Health. 2017;9(1):52-8. doi: 10.1177/1941738116674895
https://doi.org/10.1177/1941738116674895...
. Despite the training time and weekly frequency being associated with greater experience in the exercises, there is the increase in exposure of the practitioner to repetitive movement, which increases the chances of injury2727. Montalvo AM, Shaefer H, Rodriguez B, Li T, Epnere K, Myer GD. Retrospective injury epidemiology and risk factors for injury in CrossFit. J Sports Sci Med. 2017;16(1):53.. Furthermore, one of the features present in the practice inside CrossFit gyms is the establishment of personal records, especially in exercises related to weightlifting, in which the individual seeks to execute the movement with the greatest possible load. This encourages practitioners to raise the load as they increase their practice time, aiming to improve their records, but also increasing the risk of injury. Hak et al.2121. Hak PT, Hodzovic E, Hickey B. The nature and prevalence of injury during CrossFit training. J Strength Cond Res. 2013. doi: 10.1519/JSC.0000000000000318
https://doi.org/10.1519/JSC.000000000000...
suggest a focus on the proper execution technique, being a more important feature than speed and number of repetitions performed.

The fact that most studies found no association between the presence of injuries and age/age group reinforces what is proposed by Weisenthal et al. (2222. Weisenthal BM, Beck CA, Maloney MD, DeHaven KE, Giordano BD. Injury rate and patterns among CrossFit athletes. Orthop J Sports Med. 2014;2(4):2325967114531177. doi: 10.1177/2325967114531177
https://doi.org/10.1177/2325967114531177...
, who claim that CrossFit is a fitness training program that can be practiced safely by individuals of a wide age range - from 18 to 69 years, but only if carried out in a safe environment.

Body regions affected and type of exercise

The shoulder was the joint most affected by injuries due to CrossFit training. According to studies, this result is related to the execution of some exercises that have been considered harmful - such as overhead squat, push press, kettlebell swing and snatch2626. Aune KT, Powers JM. Injuries in an extreme conditioning program. Sports Health. 2017;9(1):52-8. doi: 10.1177/1941738116674895
https://doi.org/10.1177/1941738116674895...
- because they have a high range of motion of the shoulder complex, a characteristic that can increase the risk of injury, since movements above the shoulder joint lead to injury due to the reduction of the subacromial space4040. Wang H, Cochrane T. Mobility impairment, muscle imbalance, muscle weakness, scapular asymmetry and shoulder injury in elite volleyball athletes. J Sports Med Phys Fitness. 2001;41(3):403..

The study by Weisenthal et al. (2222. Weisenthal BM, Beck CA, Maloney MD, DeHaven KE, Giordano BD. Injury rate and patterns among CrossFit athletes. Orthop J Sports Med. 2014;2(4):2325967114531177. doi: 10.1177/2325967114531177
https://doi.org/10.1177/2325967114531177...
showed that, for the olympic gymnastics movements present in the modality, there was significant difference between the body regions that suffered injury, the shoulder being the most injured, corresponding to more than 41% of shoulder injuries in the practitioners analyzed. The cause of this type of injury is usually associated with a decrease in the stabilization of the scapulothoracic joint. Scapular dyskinesia affects the excursion movement of this joint, overloading the glenohumeral joint4141. Kibler BW, McMullen J. Scapular dyskinesis and its relation to shoulder pain. J Am Acad Orthop Surg. 2003;11(2):142-51.), (4242. Kibler WB, Ludewig PM, McClure PW, Michener LA, Bak K, Sciascia AD, et al. Clinical implications of scapular dyskinesis in shoulder injury: the 2013 consensus statement from the 'Scapular Summit'. Br J Sports Med. 2013;47:877-885. doi: 10.1136/bjsports-2013-092425
https://doi.org/10.1136/bjsports-2013-09...
, which is usually associated to muscle imbalance, mainly due to weakness of the serratus anterior and lower trapezius fibers4343. Burkhart SS, Morgan CD, Kibler WB. The disabled throwing shoulder: spectrum of pathology part II: evaluation and treatment of SLAP lesions in throwers. Arthroscopy. 2003;19(5):531-9. doi: 10.1053/jars.2003.50139
https://doi.org/10.1053/jars.2003.50139...
), (4444. Ludewig PM, Phadke V, Braman JP, Hassett DR, Cieminski CJ, LaPrade RF. Motion of the shoulder complex during multiplanar humeral elevation. J Bone Joint Surg. 2009;91(2):378-89. doi: 10.2106/JBJS.G.01483.
https://doi.org/10.2106/JBJS.G.01483...
. The study by Summit et al. (2525. Summitt RJ, Cotton RA, Kays AC, Slaven EJ. Shoulder injuries in individuals who participate in CrossFit training. Sports Health. 2016;8(6):541-6. doi: 10.1177/1941738116666073
https://doi.org/10.1177/1941738116666073...
showed that, among the gymnastic movements that cause injury (25 out of 46) reported by practitioners, there are kipping pull-up, ring muscle-up, push-up and ring dips

In addition to the exercises derived from gymnastics, the exercises specific to olympic weightlifting that constitutes CrossFit, like overhead squat, require the placement of the shoulder joint in positions of extreme flexion, abduction and internal rotation, which increase the risk of injury4545. Gross ML, Brenner SL, Esformes I, Sonzogni JJ. Anterior shoulder instability in weight lifters. Am J Sports Med. 1993;21(4):599-603. doi: 10.1177/036354659302100419
https://doi.org/10.1177/0363546593021004...
. Due to the high incidence of shoulder injuries found in the studies, greater caution is suggested regarding gymnastic exercises and olympic weightlifting on the part of practitioners and professionals who supervise the execution of these movements, with a focus on factors such as overexertion and improper technique, factors reported by athletes to cause injuries in 35 and 20% of cases, respectively2626. Aune KT, Powers JM. Injuries in an extreme conditioning program. Sports Health. 2017;9(1):52-8. doi: 10.1177/1941738116674895
https://doi.org/10.1177/1941738116674895...
.

Previously cited in the literature as a risk during the practice of CrossFit1010. Bergeron MF, Nindl BC, Deuster PA, Baumgartner N, Kane SF, Kraemer WJ, 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(6):383-9. doi: 10.1249/JSR.0b013e318237bf8a
https://doi.org/10.1249/JSR.0b013e318237...
, cases of rhabdomyolysis were reported in one related study2424. Huynh A, Leong KE, Jones N, Crump N, Russell D, Anderson M, et al. Outcomes of exertional rhabdomyolysis following high-intensity resistance training. Int Med J 2016;46(5):602-8. doi: 10.1111/imj.13055
https://doi.org/10.1111/imj.13055...
. According to Hak et al. (2121. Hak PT, Hodzovic E, Hickey B. The nature and prevalence of injury during CrossFit training. J Strength Cond Res. 2013. doi: 10.1519/JSC.0000000000000318
https://doi.org/10.1519/JSC.000000000000...
, this may have occurred due to the inclusion of practitioners of various fitness levels, where rhabdomyolysis is to be expected in those who exercise in extremely high levels of intensity. Rhabdomyolysis is a condition not exclusive of CrossFit, since other sports, if performed strenuously, can also cause it. It usually occurs due to poor exercise prescription or execution without adequate supervision4646. Rawson ES, Clarkson PM, Tarnopolsky MA. Perspectives on Exertional Rhabdomyolysis. Sports Med. 2017:1-17. doi: 10.1007/s40279-017-0689-z.
https://doi.org/10.1007/s40279-017-0689-...
, factor of which is also associated with injuries in CrossFit, as verified in the study by Weisenthal et al. (2222. Weisenthal BM, Beck CA, Maloney MD, DeHaven KE, Giordano BD. Injury rate and patterns among CrossFit athletes. Orthop J Sports Med. 2014;2(4):2325967114531177. doi: 10.1177/2325967114531177
https://doi.org/10.1177/2325967114531177...
, where the injury rate was significantly decreased with the involvement of the instructor.

Lack of proper supervision and/or bad training prescription can result in training components like volume and inadequate load for the practitioner4747. Drew MK, Finch CF. The relationship between training load and injury, illness and soreness: a systematic and literature review. Sports Med. 2016;46(6):861-83. doi: 10.1007/s40279-015-0459-8.
https://doi.org/10.1007/s40279-015-0459-...
, especially when it comes to extreme conditioning program. This way, the trainer must possess knowledge of the peak load of each athlete in order to prevent injuries. Halson4848. Halson SL. Monitoring training load to understand fatigue in athletes. Sports Med. 2014;44(2):139-47. doi: 10.1007/s40279-014-0253-z
https://doi.org/10.1007/s40279-014-0253-...
suggests some variables that can be assessed to monitor the training load. Variables such as frequency, time, training intensity, effort, repetitions, volume, perceived exertion or fatigue, technical analysis, among others, must be taken into consideration. The monitoring of these variables is important to prevent injuries, since performance should not be the only way to verify whether training load is suitable or not for the athlete4848. Halson SL. Monitoring training load to understand fatigue in athletes. Sports Med. 2014;44(2):139-47. doi: 10.1007/s40279-014-0253-z
https://doi.org/10.1007/s40279-014-0253-...
.

The epidemiological condition of injuries in some sports and physical exercise modalities still has gaps, lacking further investigation4949. Butragueño J, Benito PJ, Maffulli N. Injuries in strength training: review and practical application. Eur J Sport Sci. 2014;32:29-47.. In this case, CrossFit stands out, as it is a type of new physical training that has shown significant growth in recent years. Consequently, the scientific literature on injuries in this modality is also novel, so it is suggested that be performed research on injuries analyzing practitioners and athletes after exposure to CrossFit in the long term in future studies, featuring prospective longitudinal studies, with better methodological conditions and specific instruments.

All selected studies in the review met 50% or more of the criteria defined by STROBE. Most of items not met were related to the description of the methods, particularly with respect to bias, sample size and treatment of quantitative variables. Aside from that, no studies reported other information such as funding. Such findings suggest the need for more detail in the description present in the Methods section in future studies, for better methodological quality.

The selected studies present limitations, as they investigated the injuries of practitioners through self-report, so the accuracy of some answers may have been impaired, demonstrating the need for the use or development and validation of specific instruments for analyzing this population. In addition, most studies were characterized as retrospective, that is, based on past data, and few studies addressed the issue of the treatment used for injuries, which can be a subject of future research.

Clinical implications

The extrapolation of the findings of this study enables professionals involved with CrossFit practitioners to identify risk factors associated with injuries, in order to act preemptively against them. Knowing the population, most affected body regions and providing proper supervision in the practice of the modality allows the practitioner to be oriented correctly, minimizing the risk of injury. Knowing that population is important for the execution of physical and functional evaluations with the modality practitioner. This can be done, for example, with assessments on the factors mobility, balance and neuromuscular control by tests such as Y balance and step down5050. Bolt D, Giger R, Wirth S, Swanenburg J. Step Down Test-Assessment of postural stability in patients with chronic ankle instability. J Sport Rehabil. 2017;1-13. doi: 10.1123/jsr.2017-0074
https://doi.org/10.1123/jsr.2017-0074...
), (5151. Coughlan G, Fullam K., Delahunt E, Gissane C, Caulfield B. A comparison between performance on selected directions of the star excursion balance test and the y balance test. J Athl Train. 2012;366-71. doi: 10.4085/1062-6050-47.4.03
https://doi.org/10.4085/1062-6050-47.4.0...
. Poor performance in those tests shows the need for greater caution for these practitioners.

CrossFit classes with little supervision and/or with a high number of practitioners should also be avoided, as the professional control over movements performed incorrectly becomes more difficult. In addition, the work leading up to the workout of the day (WOD), such as warm ups and activities for developing a specific skill must be performed.

CONCLUSION

It is concluded that the shoulders are the most commonly affected body region, followed by the back and knees, according to the studies analyzed. The injuries were reported more frequently in males and with previous injuries, often obtained in other modalities. In most studies, it was not possible to observe relations between age and the presence of injuries, characterizing CrossFit as a physical training program that can be practiced safely by individuals from 18 to 69 years.

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Publication Dates

  • Publication in this collection
    June 2018

History

  • Received
    09 Aug 2017
  • Accepted
    24 May 2018
Universidade de São Paulo Rua Ovídio Pires de Campos, 225 2° andar. , 05403-010 São Paulo SP / Brasil, Tel: 55 11 2661-7703, Fax 55 11 3743-7462 - São Paulo - SP - Brazil
E-mail: revfisio@usp.br