THE YOUNG ATHLETE
Leda A. Ghannad, Mary E. Dubon, and Cynthia R. LaBella
Sports participation is common among youth in the United States with 60 million children participating in organized sports each year (1). Total sports participation in both male and female youth athletes has been increasing steadily over the past few decades (1,2). Among high school students in particular, the number of students participating in sports increased from around 4 million in the early 1970s to 7.8 million, according to the 2014 National Federation of State High School Associations (NFHS) participation survey (2). The Centers for Disease Control and Prevention (CDC) 2013 data showed that just over half (54%) of all high school students played team sports (3). Data regarding sports participation in younger age groups are less prevalent; however, Physical Activity Council data from 2014 showed that 62% of Generation Z (born in 2000 or later) ages 6 through 14 played outdoor sports and 57% played team sports (4). A nationwide survey conducted by the Women’s Sports Foundation on kids in third through twelfth grade found even greater participation with 84% of kids surveyed indicating they played organized or team sports (5).
Despite the popularity of youth sports among both males and females today, sex disparities regarding sports participation have long existed, with historically more males participating in organized sports compared to females. According to the NFHS, approximately 3.7 million boys and only 294,000 girls participated in high school sports in 1971 (2). In the past few decades the gap between male and female youth sports participation has been closing. In 2013, the NFHS found that 4.5 million boys and 3.3 million girls participated in high school sports (2). Reasons are likely multifactorial, but largely influenced by increased access to female sports since the passage of Title IX. Title IX of the Education Amendments of 1972 prohibited sex discrimination in all federally funded education programs and activities, resulting in increased opportunities for athletic participation by females (6). The trend toward more female youth sports participation has continued to increase well beyond the 1970s when Title IX was first passed. A 2008 sports participation report of the National Council of Youth Sports (NCYS) found that, compared to its 1997 report, girls were participating in organized sports at a younger age, and compared to the 2000 report, more girls in the 16 to 18 age group were participating in sports (1).
Great strides have been made to increase female sports participation; however, still slightly more males than females participate in youth sports overall. CDC data from 2013 showed that 59.6% of male high school students were involved in team sports compared to 48.5% of female students (3). This difference may be less prevalent in younger athletes, as the NCYS 2008 sports participation report found greater sex equity in sports participation in younger age groups compared to older athletes (1).
A chart review of sports medicine clinic data from 2000 to 2009 by Stracciolini et al. suggested that boys participate in more types of sports compared to girls, with an average of 2.5 sports played by each boy and an average of 2.2 sports played by each girl (7,8). In addition to differences in overall sports participation, this study found sex disparities between the types of sports played by males and females. Compared to girls, a significantly greater percentage of boys played team sports and contact/collision sports that are associated with more acute/traumatic injuries than overuse injuries. High school sports participation data have shown similar sex differences in the types of sports played by boys and girls. The NFHS reported in 2014 that the most popular high school sports played by males, in descending order, were football, track and field, and basketball, and the most popular sports for girls were track and field, basketball, and volleyball (Table 16.1) (1,2).
TABLE 16.1: Most Popular High School Sports Based on Participation
Sex disparities in sports injury type, location, and severity exist and may be due to several factors, including differences in sports participation, anatomy, and biomechanics. A study reviewing injuries in 1,614 patients presenting to a pediatric sports medicine clinic found a significantly greater percentage of spine, hip/pelvis, and lower extremity injuries in girls and a significantly greater percentage of head, upper extremity, and chest injuries in boys (7,8). Another study of 1,421 musculoskeletal injuries presenting to an emergency department showed similar results, finding more sprains, contusions, and ankle and back injuries in girls and more fractures and hand injuries in boys (Table 16.2) (9).
High-risk sports for sustaining an injury vary by sex. One study found that football accounted for the highest percentage of sports-related injuries in boys, while soccer was responsible for the highest percentage of injuries in girls (10). When examining injury patterns in sex-comparable sports (Table 16.3), location and type of injuries differ between girls and boys. In soccer, high school girls sustain more severe knee injuries and more ligament sprains, while high school boys sustain more fractures (11). Similarly, in basketball, high school girls sustain more severe knee injuries and complete ligament sprains, while boys sustain more severe foot injuries and fractures (11). Sex disparities in sports injuries can be further discussed in the context of traumatic injuries versus overuse injuries, with different patterns seen in males compared to females.
Boys sustain more sports-related traumatic injuries and more severe injuries compared to girls, in part due to differences in the types of sports in which they participate, since males are more likely to play in contact and collision sports compared to females (7,10,11). Studies examining the incidence of pediatric musculoskeletal and/or sports-related injuries presenting to an emergency department or trauma center found that 62% to 84% of sports-related injuries presented in males (9,12,13). An epidemiologic study that examined the rate of severe injuries incurred by high school athletes in a convenience sample of 100 high schools in the United States found that the severe injury rate per 1,000 athletic exposures in all-boys sports was significantly higher than in all-girls sports (0.45 versus 0.26, respectively) (11). This difference was primarily due to the high injury rates seen in boys wrestling and football. However, for sex-comparable sports such as soccer, basketball, and baseball/softball, the severe injury rate was significantly higher in girls compared to boys (0.29 versus 0.23, respectively) (11). Both boys and girls were found to have a significantly higher injury rate during competition compared to practice, and ligament sprains and fractures were the most common types of severe injuries (11).
TABLE 16.2: Sex Differences in Injury Incidence, by Injury Location
When examining fracture incidence in particular, several epidemiological studies have found a sex disparity in pediatric fracture risk, with boys sustaining significantly more fractures than girls (7,14–17). In a study of 204 pediatric hand fractures (subjects age 17 or younger) presenting to a tertiary care center in Singapore, the male-to-female ratio of fractures was 3.2:1, and sports participation was the most common cause of injury (14). A similar Austrian study of 3,421 pediatric fractures presenting to a level 1 trauma center found a 3:2 ratio of male-to-female fractures, with a more pronounced sex difference in fracture occurrence in adolescents compared to younger children (17). Valerio et al. found that as children got older, the male-to-female ratio of time participating in sports increased and that this was likely contributing to the sex difference in fracture incidence with age (15).
TABLE 16.3: Sex-Comparable Sports
Overuse injuries are injuries that occur with an insidious onset, without a clear preceding traumatic event, and are due to repetitive microtrauma (18). Studies have shown a higher overall rate of overuse injuries in female compared to male youth athletes (7,18–21). A study on sports injuries using data from High School Reporting Information Online (RIO), a national sports injury surveillance database, found that overuse injuries represented 13.3% of all girls’ and 5.5% of all boys’ sports injuries. Girls were at 1.5 times increased risk of developing overuse injuries compared to boys and for sex-comparable sports (Table 16.3), girls had a 1.45 times increased risk of developing overuse injuries compared to boys (21). Other research showed that in collegiate athletes females had a significantly higher proportion of overuse injuries overall, but this pattern was no longer significantly different when comparing sex-comparable sports (Table 16.3) (20).
Patellofemoral pain syndrome, a type of overuse injury to the knee, is more common in females compared to males (7,8,22–24). Rates of patellofemoral dysfunction are higher in female compared to male youth, with one study finding 7.3% of female basketball players had patellofemoral pain syndrome compared to 1.2% of male basketball players (23). Patellofemoral pain syndrome was three times more common in girls than boys presenting to a sports medicine clinic, representing 14% of female youth clinic visits compared to 4% of male youth clinic visits (7,8,23).
Stress fractures are also more common in female youth athletes compared to males. A study using High School RIO data from academic years 2005 through 2013 showed that females accounted for 54% of stress fractures across all sports. In sex-comparable sports (Table 16.3), rates of stress fractures per athletic exposure were significantly higher in female compared to male adolescents (2.22 versus 1.27 injuries per 100,000 athletic exposures) (25).
Intensity of physical activity plays an important role in bone health. One study found that preadolescent and adolescent girls who participated in at least 16 hours of weekly exercise had a 1.88 times greater odds of stress fracture compared to girls who participated in less than 4 hours of weekly exercise (26). Other studies have shown that high impact physical activity provides benefit to young athletes by increasing bone mass (27). Optimal bone health in both sexes likely involves a balance between participating in enough weight-bearing physical activity to improve bone mass and avoiding excess activity that may lead to increased stress fracture risk.
Sex disparities regarding incidence and type of overuse injuries are likely multifactorial. Females are more likely than males to play sports associated with overuse injuries, such as track and field, dance, swimming, tennis, gymnastics, and cheerleading (8). Differences in anatomy, biomechanics, joint laxity, muscle strength, neuromuscular control, hormones, training, and coaching may also play a role (18–20). Furthermore, some authors postulate that females may be more likely to report injuries and seek medical care compared to males (18).
Concussion has become of increasing interest in youth sports over the past decade due to enhanced awareness of associated adverse physical, cognitive, and psychosocial effects on the athlete. According to the International Conference on Concussion in Sport held in Zurich in 2012, concussion “is defined as a complex pathophysiological process affecting the brain, induced by biomechanical forces” (28). While much is still unknown about the pathophysiology of concussion, there is evidence that differences exist between boys and girls regarding risk of sustaining a sports concussion, symptoms, and recovery (Table 16.4).
TABLE 16.4: Summary of Sex Differences in Concussion
• Males sustain more concussions per athletic exposure
• Females sustain more concussions in sex-comparable sports
Mechanism of Injury
• Males sustain more injuries via player-player contact
• Females sustain more injuries via player-playing surface and player-equipment contact
• Females display more objective impairments in cognitive function
• Females report more subjective symptoms
• Females more likely to experience prolonged recovery
• Females may require more treatment interventions
Risk Factors for Concussion
• Anatomic/biomechanical: Females have smaller head-neck mass
• Hormonal: Estrogen is possibly neuroprotective
• Cultural: Males less likely to recognize or report a concussion
Epidemiological studies have found that overall boys have a greater rate of concussion per athletic exposure compared to girls (29–31). A study of pediatric patients under the age of 19 presenting to emergency departments in the United States found that 69% of patients with concussion were male. A similar study of children between the ages of 6 and 16 found that males accounted for 71.6% of concussions presenting to the emergency department (30,31). Children above the age of 10 and 11 are most likely to sustain a concussion during sports activity (30,31). In the United States, the highest-risk sports for sustaining a concussion are football and soccer for boys and soccer and basketball for girls (29,32,33). Some studies include boys, wrestling and boys and girls lacrosse as high-risk sports as well (29,32). Outside the United States, other popular high-risk sports include ice hockey in Canada and rugby in the United Kingdom, Australia, and South Africa (34,35).
The higher incidence of concussion in boys is likely due to their greater participation in high-risk sports. However, in directly comparable sports, high school girls sustain nearly twice as many concussions as boys, and a greater proportion of total number of sports injuries in females compared to males are due to concussion (29,32,36–38). Female athletes may also be at increased risk of recurrent concussions compared to boys (32). The mechanism of injury, whether from contact with a playing apparatus, another player, or the ground, differs between sexes depending on the sport (32,36). A study by Marar et al. comparing concussion incidence among 20 high school sports found that in directly comparable sports, girls sustained a greater proportion of concussions from player-playing surface and player-equipment contact compared to boys, who suffered more injuries from player-player contact (32).
In addition to differences in concussion incidence, there are also sex differences in symptom and recovery patterns. Female athletes experience more objective impairments in cognitive function and report more subjective symptoms post-concussion compared to males (34,39–42). A study of high school- and college-aged athletes in nonhelmeted sports showed females were more than twice as likely as males to demonstrate cognitive dysfunction on neuropsychological testing post-concussion (57% versus 28%, respectively) (42). Another study showed college females were more likely than males to demonstrate poor performance on visual memory tasks post-concussion (43). Sex disparities also exist with regard to post-concussive symptoms. Several studies have shown that female athletes experience more total concussion symptoms compared to males; however, data on whether specific types of symptoms vary between males and females have been variable (40,43,44).
Sex differences are seen with concussion recovery. Female adolescent athletes may have a more prolonged recovery from a concussion compared to males. In a study of 266 adolescent athletes presenting to an outpatient sports medicine concussion clinic, 41.2% of females took more than 60 days to recover from their symptoms while half as many males, 20.7%, had a prolonged recovery of more than 60 days (33). Conversely, a study examining post-concussive symptoms in subjects 3 months after sustaining a sports-related concussion found that among athletes under 18 years of age females had similar symptom scores to males; however, for subjects age 18 and older, females had higher symptom scores than males (45). Thus, recovery patterns may vary based on age group and patient population. Female athletes have also been found to require more treatment interventions in addition to physical and cognitive rest, such as academic accommodations, vestibular therapy, or medications, to augment their recovery compared to male athletes (33).
The higher incidence of sports concussion in females, increased symptoms, and neurocognitive deficits post-concussion are likely due to a combination of anatomic, hormonal, biomechanical, and cultural risk factors (37,46). Anatomic risk factors include differences between male and female head and neck sizes (46,47). In a study of male and female collegiate soccer players, head-neck segment length was 7% shorter and head-neck segment mass was 20% lighter in females compared to males (46). In a similar study of physically active young adults, women had 30% shorter neck girth and 43% lighter head mass compared to men (47). These anatomic differences may cause alterations in biomechanics that place females at a higher risk of sustaining a sports concussion; however, data to support this remain inconsistent. Tierney et al. found that women had more head-neck segment angular acceleration, angular displacement, and muscle activity in response to force application and less head-neck stiffness and isometric neck muscle strength compared to men (47). In another study of high school soccer athletes, females sustained significantly more concussions via player-ball contact through heading compared to males. These studies lend support to the theory that biomechanical factors involving the head and neck play a role in the sex disparity in concussion incidence (32). In contrast, Mansell et al. found no difference in head-neck kinematics, neck stiffness, and electromyography (EMG) neck muscle activity between male and female subjects (46). Mansell et al. speculated that their cohort of soccer players had better neuromuscular adaptations to handle head-neck loads as part of their soccer training compared to a general population of physically active young adults in the Tierney et al. study, and that this could account for the difference in their findings (46).
Hormonal factors may also contribute. Rat studies have shown that estrogen in females may be neuroprotective and may result in superior outcomes in female rats following brain injury (48). However, human studies exploring the effects of hormonal differences between males and females on concussion are lacking.
Psychosocial differences appear to play a significant role, as males may be more likely to underreport their symptoms. A survey of over 1,500 male high school varsity football players showed that only 47.3% of respondents who admitted to having a concussion post-season reported their symptoms during the season (49). The most common reason for underreporting was thinking the injury was not serious enough to report, followed by (in descending order of frequency) not wanting to leave the game, not knowing their symptoms could be a concussion, and not wanting to let their teammates down (49). A study of high school athletes across multiple sports showed that females had a better knowledge of how to identify a concussion and were more willing to report concussion symptoms or stop play due to symptoms compared to males (50). High school males are also more likely than females to be noncompliant with return-to-play guidelines and resume sports prior to full recovery (38). Additionally, female athletes may be treated with more sympathy by coaches and adults, while male athletes may feel more pressure to “tough it out.” In a study regarding youth and parents’ perceptions of concussions, mothers were more likely than fathers to think concussion was a critical issue, and boys were more likely than girls to report that their friends would think they were “dumb” for caring about concussions (51).
SEX DIFFERENCES IN RULES OF SPORT
Rules of play are similar between boys and girls in many popular youth sports including tennis, soccer, and basketball; however, there are a handful of youth sports with rules that are considerably different between males and females, leading to different injury rates and patterns. The next sections are brief discussions of popular sports that differ between sexes, including lacrosse, ice hockey, softball, and baseball.
Lacrosse is a team sport of increasing popularity with nearly 400,000 youth participants and slightly more male participation (65%) than female, according to the 2013 U.S. Lacrosse Participation Survey (52). Rules and equipment differ substantially between girls and boys lacrosse (Figure 16.1). Required protective equipment for male youth field players consists of a helmet, mouth guard, shoulder and arm pads, gloves, and a protective cup. Rib pads are optional (53). Female youth field players required protective equipment is less extensive and includes a mouth guard and goggles, with optional gloves and optional soft headgear (54). In boys’ lacrosse the field stick can vary in length depending on the position and has a deeper pocket, while in girls’ lacrosse the stick length remains constant among players and has a shallower pocket. The design of the boys’ field stick requires more aggressive play to dislodge the ball from the deeper pocket compared to the girls’ field stick.
The differences in protective gear and playing equipment are due to sex differences in rules of play. Boys’ lacrosse is considered a full-contact sport allowing for intentional stick checking at all levels and body checking in participants older than 11 years of age. For girls, body checking is prohibited, modified stick checking is allowed in girls age 10 to 12, and full stick checking is allowed in girls older than 12 (55).
The differences in rules and equipment result in different injury patterns. A study of high school lacrosse players showed injury rates were 1.5 times higher in males than females (56). Males are more likely than females to be injured during player-player contact, while females are more likely to be injured during contact with a playing apparatus or due to overuse (56,57). The most common injuries in both sexes are sprains/strains, followed by contusion or concussion (56,57). High school boys playing lacrosse are more likely to sustain a concussion compared to girls, and this increased risk is more prevalent in players aged 11 to 14, where body checking is allowed (29,56–58). Boys’ lacrosse is a full contact sport, which leads to more sports injuries compared to girls, despite the increased protective equipment worn by boys.
Ice hockey is played by over 350,000 youth in the United States, 85% of whom are male (59). Female youth participation is similar in Canada, where ice hockey is considered a national pastime, with females estimated to be about 14% of youth ice hockey players (60). The primary rule difference between female and male ice hockey is that females are not allowed to body check, while body checking is allowed in males older than 13 years of age in the United States and Canada.
Approximately 90% of ice hockey injuries presenting to U.S. emergency departments are in males; however, the proportion of injuries in females increased from 5% of all ice hockey injuries in the 1990s to 9% from 2000 to 2006 (61). In a Canadian study of youth ice hockey players, females had significantly more soft tissues injuries, sprains/strains, and injuries due to falls while males sustained more fractures, upper extremity injuries, and injuries due to body checking (60). In both sexes, adolescent athletes are at highest risk of injury (60). A study of ice hockey injuries presenting to U.S. emergency departments showed that females accounted for a higher proportion of the head injuries and concussions while males accounted for more facial injuries and fractures (61). Although female hockey players have a higher incidence of concussion compared to males, a study by Brainard et al. found that collegiate female ice hockey players sustained significantly fewer head impacts per season compared to males (62).
The overall injury rate is nearly twice as high for males compared to females (approximately 4 versus 2 injuries per 1,000 athlete exposures (AEs), respectively) (63). Body checking allowed in male leagues likely plays a large role. Body checking has been found to increase the risk of all injuries in male ice hockey players twofold to fourfold, as well as increase the risk of concussion (63,64). Due to the high risk of injury with body checking, the American Academy of Pediatrics issued a policy statement in 2014 recommending expansion of nonchecking leagues for boys older than age 15, no checking in games prior to age 15, and restricting body checking to the highest competition levels (64).
Softball and Baseball
Baseball and softball are popular sports in youth athletics with relatively low risk of injury compared to other sports (65,66). Males primarily play baseball, while softball is a female-dominated sport. Although the objective of each game is similar, key differences exist (Table 16.5). In high school, the baseball field is larger than the softball field and the mounds are farther apart. A baseball is smaller, with a higher coefficient of restitution than a softball, and is made of leather, whereas a softball may have a synthetic covering (67). In terms of protective equipment, players of both sports wear gloves and a batting helmet. Softball players are required to have a face mask attached to their helmet, while this is optional in baseball players (67). Rules for batting and fielding are similar between the sports; however, the pitching mechanics and average pitch counts differ considerably in baseball and softball. The baseball pitch is overhand and is performed from an elevated mound 60.5 feet from home plate, while the softball pitch is an underhand windmill pitch delivered from a flat pitching circle 40.0 feet from home plate (68). Despite these differences, joint loads at the shoulder are similar in youth softball and baseball pitchers (68). However, softball players are less regulated in their pitch counts, with a high school softball player often pitching 1,200 to 1,500 windmill pitches in a 3 day period compared to 100 to 150 pitches made by a baseball pitcher in the same time period (68).
Much of the data regarding sex differences in baseball and softball injuries are focused on high school athletes. Rates of severe injuries are similar in boys’ baseball and girls’ softball (0.19 versus 0.18 per 1000 AEs, respectively) (11). Female softball players sustain significantly more knee injuries, ligament sprains, and dislocations than male baseball players (11). Males are more likely to be injured during pitching, while females are more likely to be injured while batting or being hit by a pitch (11). Concussion injury data have been mixed. One study showed female softball players had a higher rate of concussion than male baseball players (1.6 versus 0.5 per 10,000 AEs, respectively), while another study showed similar concussion rates between the sports but a greater proportion of total softball injuries due to concussion (32,36).
Upper extremity injuries involving the shoulder and elbow are common in both baseball and softball. One study found that the incidence of shoulder injuries was significantly higher for boys’ baseball than for girls’ softball (1.72 versus 1.00 injuries per 10,000 AEs) (69). Muscle strains and incomplete muscle tears were the most common shoulder injuries in both sexes and occurred more frequently during practice. Female softball players were more likely to be injured during throwing while males were more likely to be injured during pitching (69). Pitching injuries were more likely to require surgical treatment in both sexes; however, baseball pitchers were twice as likely to sustain a shoulder injury compared to softball pitchers (69). This is likely because the baseball pitching motion, combined with faster pitching speed, generates more force at the shoulder and elbow than the softball pitching motion (69).
TABLE 16.5: Summary of Select High School Baseball and Softball Rule Differences
Base path distance (feet)
Pitching distance (feet)
May or may not be underhand
Must be underhand
Ball weight (ounces)
Ball circumference (inches)
Batting helmet face mask
Caps, visors, and headbands optional
Source: Adapted from Ref. (67). Pecora A. 2015 Baseball Softball Rules Differences. Indianapolis: National Federation of State High School Associations (NFHS); 2015. https://www.nfhs.org/media/727147/2015baseballsoftballrulesdifferences.pdf
Little league elbow is a common overuse injury unique to young (skeletally immature) throwing athletes, particularly pitchers. It is caused by a traction apophysitis on the medial epicondyle of the humerus at the origin of the common flexor tendon. A similar overuse injury can occur at the proximal humeral epiphysis, called little leaguer’s shoulder. In an attempt to decrease the risk of overuse injuries, youth baseball leagues limit pitching counts per week and per day based on the age of the athlete; however, similar regulations are lacking in youth softball leagues (66). More research is needed regarding whether restricting pitching counts in youth softball players could help decrease risk of injury.
PUBERTY, JUMPING MECHANICS, AND NEUROMUSCULAR CONTROL
Anthropometric Changes in Puberty
Puberty is defined as the process through which a child biologically becomes an adult and includes development of adult height, secondary sex characteristics, and the capacity for reproduction. Sexual maturity can be evaluated using the Tanner staging system, which uses secondary sex characteristics to differentiate stages of puberty (Table 16.6). The onset of pubertal changes occurs earlier in females compared to males. In females the mean onset of puberty is between 8 and 12 years of age and is marked by the development of breast buds. Menstruation occurs approximately 2 to 2.5 years later at a median age of 12 (range: 9 to 16 years of age). In males, the mean onset of puberty is between 11 and 13 years of age and is marked by testicular enlargement (70,71).
Accelerated growth occurs early in puberty for boys and girls; however, males demonstrate a longer prepubertal growth period and greater growth velocity compared to females (72). Boys reach their peak growth velocities 2 to 3 years after girls and typically continue to grow 2 to 3 years after girls have stopped growing (70). Average mature male height is taller than average mature female height (69.4 versus 63.8 inches, respectively) (73). This difference is primarily due to leg length as opposed to trunk length. Boys develop a significantly greater increase in leg length compared to females due to the longer prepubertal growth period (72,74).
Prior to puberty, girls and boys are similar in terms of their body composition. There is a significant divergence in body composition, including lean muscle mass, fat mass, and bone mass, between females and males during puberty. This is due to differences in gonadal hormones and other endocrine factors (74,75). Prepubertal muscle mass, also referred to as lean mass or fat-free mass, is fairly similar between males and females. During puberty, boys gain significantly more muscle mass and strength compared to girls (76–86). At age 12 to 14, female muscle mass plateaus and male muscle mass continues to increase at an accelerated rate due to a rise in testosterone (75,87). The distribution of muscle mass also differs, with males developing significantly more upper body muscle mass and strength compared to females (74,82,87,88).
TABLE 16.6: Tanner Staging/Sexual Maturity Rating