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Original Research

Sex Differences in “Weightlifting” Injuries Presenting to United States Emergency Rooms

Quatman, Carmen E1,2; Myer, Gregory D1,3; Khoury, Jane1,4; Wall, Eric J1,5; Hewett, Timothy E1,6

Author Information
Journal of Strength and Conditioning Research: October 2009 - Volume 23 - Issue 7 - p 2061-2067
doi: 10.1519/JSC.0b013e3181b86cb9
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Abstract

Introduction

Since the passage of Title IX of the Educational Assistance Act in 1972, women's participation in high school sports has increased more than 9-fold with more than 3 million women participating in sports during the 2006 to 2007 school year (40). The increase in women's sports participation has lead to a resultant increase in injuries in this population. In particular, the number of knee injuries has increased dramatically (1-3,6) and adolescent women more commonly experience overuse injuries, such as patellofemoral pain (5). Women athletes participating in sports also have a greater propensity for the development of the female athlete triad (low energy-level availability, menstrual disorders, and bone loss), which may progress into significant long-term problems such as eating disorders, amenorrhea, and osteoporosis (38).

Recent evidence indicates that training programs that incorporate resistance training can reduce injuries while improving sports-related performance in women athletes (16,21,25,26,33-35). Consequently, resistance training is gaining popularity in women's sports populations (40). Resistance training may also reduce the propensity for the development of the female athlete triad and increase self-esteem and body image satisfaction in women athletes (4,43). Although the use of resistance training in women has increased dramatically in the past 2 decades, an extensive literature search revealed few studies reporting risks involved with resistance training participation in women.

The objective of this investigation was to evaluate sex differences for strength training injuries in adolescents and young adults presenting to U.S. emergency rooms by type (sprains and strains, fractures), mechanism (accidental, nonaccidental), and location (head, trunk, arm, hand, leg, foot) of injury. We hypothesized that there would be sex differences in accident-related injuries that would be potentially reflective of supervision and experience. We also hypothesized that there would be increased trunk injuries during strength training in men relative to women indicative of relative resistance training intensity.

Methods

The U.S. Consumer Product Safety Commission (CPSC) National Electronic Injury Surveillance System (NEISS) was queried from 2002 to 2005, using the CPSC code for “Weightlifting” (Product ID # 3265). The NEISS database is a national probability sample of the hospitals in the United States and U.S. territories with sampling sites spread throughout the country. Sampling weights provided by CPSC were used to account for study design in the analysis and to calculate national injury estimates. Subjects between the ages of 14 and 30 years were included in the study. Injuries sustained under the influence of alcohol or other recreational drugs as reported by the hospital staff, injuries that were categorized as strength training but were not associated with strength training in the gym (e.g., hurt while shopping at a sporting goods store), subjects that did not have a clearly defined mechanism of injury, or subjects who left without seeing a physician were eliminated from the sample (378 subjects were eliminated from a total sample of 4,091). All data were quality controlled by cross-referencing the specific comments to the CPSC category code. Type of injury (sprains/strain or fracture) and body location of injury (head, arm, trunk, leg, foot) were reported for each subject. In addition, each injury was classified into a mechanism of injury termed “nonaccident” or “accident” based on the specific comments in the CPSC category. The mechanism of injury was considered nonaccidental if it resulted from exertion (sprain/strain, fatigue failure, headache), equipment malfunction (cable snapping, resistance bands breaking), or overuse (tendonitis). The mechanism of injury was considered accidental if it resulted from dropped weights, improper use of equipment, or tripping over equipment. The mechanism of injury was categorized by 2 separate reviewers blinded to both age and sex of the subjects. One reviewer performed the initial categorization, whereas the second reviewer performed a separate, independent categorization while performing a quality control audit of the data. If the reviewers were unable to reach an agreement about the mechanism of injury or if the reviewers were unable to determine the injury mechanism from the description, the data were excluded from the sample. The differences between sexes were determined for type, mechanism, and location of injury. In addition, the “accidental” injuries were screened out and additional analyses were run to determine type and body part injured for “true” strength training injuries.

Statistical Analyses

Statistical analyses were performed using SAS, version 9.1 (SAS Institute, Cary, North Carolina, United States). To account for the survey design and to use the appropriate standard errors, the survey-specific procedures, which incorporated the sample weights and design clusters, were used for analysis. The independent variable of interest, sex, had 2 categories: Man and woman. Weighted Chi-square analysis was used for the initial comparison of the proportion of type of injury, accidental vs. nonaccidental, and sprain/strain vs. nonsprain/strain for men and women. Weighted logistic regression was used to further elucidate the gender differences and to estimate the odds ratio (OR) and associated 95% confidence interval (CI). The level of statistical significance was established a priori at p < 0.05.

Results

A total of 3,713 (3,102 men and 611 women) patients treated at participant NEISS emergency rooms between January 1, 2002 and December 31, 2005 met the inclusionary criteria for the analysis of strength training injuries. Hence, women comprised 16.5% of the population. Based on the NEISS database sampling weights, an estimated 114,441 men and 22,592 women between the ages of 14 and 30 were treated in U.S. emergency rooms for strength training injuries from 2002 to 2005. Therefore, an approximate 6 to 1 disparity in strength training injuries prevalence was observed between men and women from this sample. This disparity remains when the accidental injuries are removed, resulting in cohorts of 77,145 men and 12,458 women.

Comparisons between the sexes for accident-related injuries showed that women had significantly higher odds of accidental strength training injuries compared to men (p < 0.001, OR = 1.69; 95% CI = 1.37 to 2.08; Table 1). Specific anthropometric categorization of accidental injuries revealed that women had a higher odds of accidental foot injuries compared to men (p < 0.001, OR = 2.44; 95% CI = 1.75, 3.45), whereas men demonstrated increased odds of accidental hand injuries compared to women (p < 0.001, OR = 2.14; 95% CI = 1.49, 3.07).

T1-21
Table 1:
Accidental and sprain/strain strength training injuries.

When overall injuries were evaluated, men had significantly greater odds of sprains and strains (p = 0.004, OR = 1.34: 95% CI = 1.10 to 1.65) compared to women (Table 1). There was no difference in reported fracture injuries from strength training between the sexes (p = 0.37). The trunk was the most commonly injured body part for both men (36.9%) and women (27.4%, Figure 1). However, men had significantly greater odds of trunk injuries compared to women (p < 0.001, OR = 1.55; 95% CI = 1.25 to 1.96). Women reported greater odds of foot (p < 0.001, OR = 2.63; 95% CI = 2.04 to 3.45) and leg (p = 0.03, OR = 1.54; 95% CI = 1.05 to 2.22) injuries compared to men.

F1-21
Figure 1:
Percentage of injuries at each body location for women and men. Note that the small prevalence of head injuries in the female category provides invalidated results and should be interpreted with caution.

Discussion

In the current study, women comprised only 16.5% of the overall strength training injuries in the study population, an approximate 6 to 1 disparity. This disparity is likely a reflection of the lower number of women participating in resistance training activities, rather than of women suffering injuries “less often” than men during resistance training. Resistance training is considered a popular and effective form of conditioning for sports performance enhancement and is commonly incorporated into most sports training programs for men (13). Unfortunately, the only strength training participation sex ratio data available are at the high school level from the National Federation of State High Schools (NFHS) Athletics Participation Survey and no epidemiology studies have been published regarding strength training participation at any level.

Prior to Title IX, participation of women in high school strength training was uncommon (NFHS database, Figure 2). However, because women's participation in sports has increased over the past 3 decades, the prevalence of women participating in high school strength training has likely also increased. Despite this relative increase, the sex difference in strength training participation remains much greater than the sex difference in overall sports participation (Figures 2 and 3). Participation estimates from the High School Athletics Participation Survey conducted by the NFHS during the 2004 to 2005 school year show that the ratio of men to women for overall sports participation was 1.4:1, whereas the ratio for strength training was 3:1 (39). Although no current epidemiology studies are available to determine whether there is a sex difference in resistance training participation, the NFHS survey indicates that a 3:1 man to woman sex discrepancy most likely exists (40). Unfortunately, little data are published in the literature to warrant an objective strength training incidence rate sex comparison at this time.

F2-21
Figure 2:
Reported high school strength training participants after the induction of Title IX (school years 1973-2005) based on the participation estimates from the High School Athletics Participation Survey conducted by the National Federation of State High School Associations.
F3-21
Figure 3:
Reported high school sports participants after the induction of Title IX (school years 1973-2005) based on the participation estimates from the High School Athletics Participation Survey conducted by the National Federation of State High Schools Associations.

The higher risk of accidental injuries in women athletes found in this analysis is of particular concern. Common accidental injuries included dropped weights, improper use of equipment, or tripping over equipment-many of which may have been prevented with proper education and supervision. Resistance training is an integral component of most high school and collegiate football, wrestling, baseball, and basketball training programs. These factors reflect that most sports training programs for men allocate significant staffing and supervision to improve the efficacy and safety of their training programs. In comparison, women may not have similar access, desire, or available resources to incorporate resistance training into their sports programs. Women, and their coaches, may also have concerns relating to increased injury or other perceived potential negative side effects of strength training participation. Because women have lower participation numbers in resistance training than men (40) these findings may indicate that women may not have adequate supervision or proper education in resistance training techniques.

If an athlete performs resistance training exercises inappropriately at low resistance levels, then the risk of injury will be amplified at higher resistance levels. Women may benefit from resistance training programs that provide strict safety guidelines, education, and appropriate supervision with emphasis on proper lifting techniques.

The higher risk for lower-extremity injury in women compared to men is consistent with reports in other sports activities (1,6,42). Although the percentages of leg injuries were relatively low in both sexes, the higher risk in women could indicate underlying neuromuscular deficits. Several studies have shown that neuromuscular training that incorporates resistance training can reduce knee injuries in adolescent and mature women athletes (21,31,37). Thus, a properly supervised resistance training program could be of particular importance for women in reducing not only resistance training injuries, but also in reducing injuries during sports competition (36).

The higher risk of sprains and strains in men compared to women in this study is an interesting finding. Sprains and strains often result from exertion during activity. Men may train at higher relative intensity levels during resistance training, lifting heavier weights and attempting more difficult lifting techniques than women. This may put them at higher risk for developing exertion-type injuries such as sprains and strains. Moreover, men had significantly more trunk-related injuries than women, which may be reflective of inappropriate selection of resistance intensity by male athletes. Coutts et al. (12) demonstrated that supervised resistance training improved strength gains and exercise adherence in young athletes vs. unsupervised training. Mazzetti et al. (32) corroborated these findings when they found similar results in male athletes who had moderate experience with resistance training. Cumulatively, there is strong evidence to support the benefits of direct supervision to improve both the efficacy and safety of resistance training applied to young athletes. In addition, appropriate progressions of intensity of the resistance exercises, while maintaining the quality of exercises, may be critical in achieving successful outcomes from resistance training (23).

A well-designed resistance training program can increase strength in female athletes (7,9,10,15). Resistance training may provide significant performance and injury prevention benefits to women because they often display decreased baseline levels of strength and power compared to men (19,22,28). Myer et al. demonstrated that women may improve strength measures as much as 92% with just 6 weeks of training (35). Moreover, although both men and women show similar growth and development patterns associated with puberty, the sexes demonstrate significant differences in neuromuscular patterns after the onset of puberty (8,29). During puberty, men often demonstrate increases in power, strength, and coordination, whereas no similar increases have been demonstrated in women (8,29). Musculoskeletal growth during puberty, in the absence of a corresponding neuromuscular spurt, may lead to neuromuscular imbalances (20) and place women athletes at risk for injury (17,18). Participation in resistance training programs may help women athletes achieve a neuromuscular spurt (27,30) similar to the spurt experienced by men.

Another major clinical problem unique to women athletes is the female athlete triad. The female athlete triad encompasses 3 medical conditions (low energy availability, menstrual disorders, and low bone mineral density) that often overlap in athletic women. These conditions may lead to significant long-term health problems such as infertility, osteoporosis, and eating disorders (38). In the past, many women have been afraid to participate in resistance training because of a fear of “bulking up.” Intensive neuromuscular training significantly increases fat-free mass in adolescent women (41). However, studies have shown that women who participate in resistance training programs feel healthier and more fit and have an improved body image (4,43). Ahmed and colleagues studied women who participated in a 12-week resistance training program and then they questioned participants about body image, health, and fitness (4). Results of this study showed that the women who participated in the resistance training program felt more confident, toned, healthier, and more positive about their body (4). Thus, resistance training may help counteract female athlete triad conditions by improving self-esteem and body image satisfaction and by increasing fat-free mass, bone mineral density, and the strength of tendons and ligaments (14,24).

The limitations of the current study are mainly associated with the NEISS dataset. The categorizations for injury caused by a strength training activity and for mechanisms of injury (accident or nonaccident) are limited by the coding and comments provided by treating emergency room clinicians. Although the NEISS database has a specific code related to “weightlifting,” it is possible that the injuries reported were not necessarily a result of resistance training activities. The database reflects injuries that occur while using a specific product (weights or resistance training equipment) and it is dependent on individual treating clinicians to determine whether the injury falls under the code for “weightlifting.” However, in addition to coding, emergency room clinicians provided specific comments linked to each injury mechanism in the NEISS database. This allowed the investigators to assess the injury mechanism and “weightlifting” activity to confirm the data quality control. Although the data categorization for mechanism of injury was not totally objective in nature because it was limited by the interpretation of the investigators, the reviewers were blinded to age, sex, and overall injury estimates to increase the level of objectivity.

As a result of the broad categorizations used for database coding, the information derived from studies using the NEISS database must be carefully evaluated and interpreted. It is important that study questions, hypotheses, and methods are established before using the database because the same database may reveal different results depending on the dates used for review and the inclusionary/exclusionary criteria used to study a specific question and test hypotheses. For the current analysis, the years 2002 to 2005 were used to sample the NEISS database because 2002 to 2005 were the most recent years digitally available from the CPSC at the time of sampling. In addition, the age range (14-30 years) chosen for inclusionary criteria in this study was selected to reflect the age groups most likely to engage in resistance training activities on a consistent basis (high school, college, and young adult). Thus, the results for the current analysis should only be used to describe the sex differences in strength training injuries for the age ranges of 14 to 30 years.

At the same time, it is unknown whether multiple visits were made by the same person to the emergency room for a specific strength training injury. If the same person reported to the emergency room multiple times, this would lead to an overestimation of the overall injury prevalence. However, the NEISS coding manual instructs hospital workers to record only the first emergency room visit for any specific injury (11); thus it is unlikely that multiple visits by the same person for a specific injury were recorded. In addition, the NEISS coding manual instructs hospital workers to record only the most severely affected body part associated with an injury incident. Thus, the frequency of additional minor injuries accompanying an injury incident may be underrepresented. The dataset is not all-encompassing in terms of “weightlifting” injuries because we cannot account for injuries that may not have resulted in an emergency room visit because treatment was available at the setting of injury (e.g., athletic trainers or team physicians), treatment was sought at other medical facilities, or treatment was not sought out for an injury.

Injury rates by sex and age could not be calculated because the denominator, accurate numbers of adolescents and young adults participating in resistance training activities, and the associated exposure time are not available. Finally, these data cannot be generalized to athletes, skill level, or physical fitness because the NEISS database does not distinguish among recreational, high school, or collegiate athletes or whether the strength training injury occurred during “structured” (developed programs monitored by coaches, teachers, or trainers) or “unstructured” (no formal program or supervision) activities.

Despite these limitations, the results presented in this study provide important information about strength training injury patterns of high school and college-aged populations. To our knowledge, no data are available that compare men's and women's resistance training injuries and this study is the only nationally representative stratified probability sample of strength training injuries categorized by age, sex, and mechanism of injury that resulted in U.S. emergency room visits. A controlled case study or cohort study may provide “more accurate” results; however, the logistics of such a study that would capture enough resistance training injuries to reach adequate power for analyses would be challenging. Although the limitations to this study are known, this information provides the groundwork necessary to establish differences in men's and women's resistance training injuries. Future work should focus on the determination of whether technique training, proper supervision, stricter safety guidelines, or other modifications can make resistance training safer for both sexes at all ages and levels of participation.

Practical Applications

During strength training activities, women demonstrated a higher risk of accidental injuries and suffered more lower-extremity injuries compared to men. Men, however, suffered more exertional-type resistance training injuries such as sprains and strains compared to women, particularly at the trunk. To reduce the occurrence of accidental injuries in women, an emphasis should be placed on safe equipment use, proper lifting techniques, stricter safety guidelines, and appropriate supervision. To reduce the occurrence of exertional injuries in men increased supervision to improve techniques at high intensity and improve appropriate resistance intensity selection may be beneficial for both sexes.

Acknowledgments

Financial support was provided from the National Institutes of Health/NIAMS Grant R01-AR049735. The authors would like to acknowledge funding support from National Institutes of Health/NIAMS Grants R01-AR049735, R01-AR05563, and R01-AR056259.

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Keywords:

strength training; resistance training; power lifting; injury incidence; injury rates

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