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Physical Activity & Sport in the Lives of girls
Introduction DON SABO, PH.D., D’YOUVILLE COLLEGEWHEN THE PRESIDENT’S COUNCIL ON PHYSICAL FITNESS AND SPORTS was established by Executive Order in 1956, few Americans could have imagined the surge of participation in physical activity and sport among girls and women over the last two decades. Millions of girls now participate in a rapidly expanding variety of physical activities, and female athletes perform feats that once were deemed physiologically impossible. Despite the startling speed of these recent changes, however, the explosion of women’s participation and ability is more accurately viewed as an acceleration of a centuries-long march toward greater physical freedom and athletic excellence. During the nineteenth century, health reformers and educators included “female gymnastics,” walking, riding and dancing as key components of young women’s education (Vertinsky, 1994). In the countryside and towns, archery, tennis, bicycling, ice boating, roller skating, croquet, golf and dance became popular among girls and women. A “new model of able-bodied womanhood” emerged, which challenged traditional notions about female frailty and ladylike behavior (Verbrugge, 1988, p. 196). The integration of exercise and athletic activity into school curricula expanded during the twentieth century. Recreational athletics for girls became popular in the form of “play days” between 1920 and 1950 and competitive varsity sports such as basketball and track and field multiplied after World War II (Hult, 1994). The passage of Title IX in 1972 ushered in an era of coed physical education and greater opportunities for girls to play high school and college sports. The fitness revolution also grabbed the attention and allegiance of millions of girls and women during the 1970s and 1980s. Physical Activity and Sport in the Lives of Girls: Physical and Mental Health Dimensions from an Interdisciplinary Approach presents an interdisciplinary portrayal of the connections among the physical, psychological, social and cultural aspects of physical activity and sport in girls’ lives. When viewed collectively, the research findings discussed here show how physical activity and sport impact the “complete girl”: that is, the many interrelated aspects of a girl’s life ranging from musculoskeletal and cardiovascular functioning, to psychological well-being, gender identity, relationships with friends and family and performance in school. Physical activity and sport offer girls more than gateways to fun, competition or an elevated heart rate. While the authors of this report are aware that girls’ experiences vary a great deal, the vision of the complete girl fosters a comprehensive awareness that exercise and sport are not just about physical movement but personal development, identity and values as well. PARTICIPATION, OPPORTUNITY AND BARRIERS American girls now participate in a wider range of physical activities and sports, and at more levels of competition, than ever before in our history. While Oregon girls learn to square their shoulders to the volleyball net, a group of girls play “four squares” in rural New Hampshire, an Arkansas teenager teaches hopscotch to her little sister, and Native American teenagers meet for lacrosse practice. As girls bounce and chatter through double-dutch jump rope in Bedford-Stuyvesant, in-line skaters glide through a Houston suburb. As an Ohio high school basketball team runs through drills, friends from DeKalb, Illinois, meet for an aerobics class. And women give gutsy performances while winning gold medals at the 1996 Summer Olympic Games in sports ranging from softball, soccer and basketball to gymnastics, track and field and swimming. Females have become prime movers in the fitness realm. A recent nationwide survey conducted by the National Sporting Goods Association indicated that more women (55.4 million) than men (43.4 million) participate in several leading fitness activities—aerobic exercising, bicycling, exercising with equipment, exercise walking, running and swimming. A more specific breakdown reveals that an estimated 18.3 million women do aerobics, 26.5 million bike for exercise or mountain bike, 23.8 million exercise with weights, 45.2 million walk, 8.65 million run or jog and 32.6 million swim (National Sporting Goods Association, 1995). Girls’ participation in school athletic programs and community-based programs is also mushrooming. Girls now comprise about 37 percent of all high-school athletes, representing an increase from one in 27 girls who participated in 1971 to one in three girls in 1994. The ratio for boys during this timeframe remained constant at one in two. In 1994–1995, 2,240,000 girls participated in high-school sports, compared to 3,554,429 boys, 37 percent and 63 percent respectively (National Federation of State High Schools Associations, 1995–1996). In terms of some specific sports, an estimated eight million girls under age 17 played basketball in 1994 (compared to 12.5 million boys) while 6.7 million girls played soccer. As more girls developed athletic interests and physical skills at the grassroots levels of competition during the 1970s and 1980s, participation in college and Olympic sports also exploded. Women now comprise 33 percent of all college athletes and approximately 39 percent of United States Olympic team members. Reciprocally, as more female role models become available for young girls to emulate, their interest and involvement in fitness and athletic activities will continue to grow. Despite these gains, it is important to realize that women’s historical trek toward greater physical and athletic opportunity has been filled with barriers. In the past, various individuals have condemned exercise and sport as unladylike and eminent physicians warned women against overstrain and sterility. One of the authors of this report, sport sociologist Margaret Duncan, points out that stereotypes associated with traditional notions of femininity and masculinity exalted boys’ strength and athletic feats while equating girls’ athletic talents with “tomboyism.” Parents, coaches and teachers often encouraged boys to test their physical and emotional limits while ignoring or coddling girls. Today, girls’ achievements in physical activity and sport remain overshadowed by the cultural prominence of men’s sports. In school and community-based programs, boys still receive a disproportionate share of opportunities to participate in exercise and sport. Male-dominated sports organizations remain mired in policies and beliefs that shortchange girls and women, and parents or advocates of girls are forced to wage expensive legal battles in the pursuit of gender equity. Indeed, it is unlikely that the large increase in girls’ athletic participation and growing cultural acceptance of physically active and athletic females would have occurred without the passage of Title IX (Birrell & Cole, 1994; Cahn, 1994a; Messner & Sabo, 1990). Pressured by the perceived threat of lawsuits or payment of legal fees, and pulled by increasing demands for greater opportunity for girls, Parent Teacher Associations and school administrators began to rethink traditional clichés like “girls just aren’t as physical as boys” or “sports are more important for boys than for girls.” And finally, harsh economic conditions, prejudice and institutional barriers have limited the participation of many poor girls, girls of color and girls with disabilities. Ironically, where the real and potential health outcomes of physical activity and sport are probably most needed, participation rates and access to resources are most lacking. As the authors of this report repeatedly document, girls’ increasing participation and interest in physical activity and sport bode well for their health. Yet these positive national trends are being undermined by the growing numbers of adolescents who are becoming sedentary and obese, the substantial numbers of girls who are dropping out of sports, and the persistence of social and economic barriers that limit girls’ opportunities to develop physically active lifestyles. UNDERSTANDING THE COMPLETE GIRL Physical activity and sport are not simply things young girls do in addition to the rest of their lives, but rather, they comprise an interdependent set of physiological, psychological and social processes that can influence, and, in varying degrees, sustain girls’ growth and development. The interdisciplinary approach that underpins this report is designed to make more visible some of the connections among physical activity, sport and the rest of girls’ lives. Some examples of the broader linkages that are examined in the body of this report are highlighted below. Psychological Well-Being Within the traditional framework of psychoanalytic theory, nonconformity to traditional gender expectations was considered pathological. Hence, women’s interest and involvement in business, science, sport or other “masculine” activities were clinically suspect. In contrast, the review of psychological research presented in this report shows that physical activity and sport are apt to strengthen rather than worsen the psychological health of girls. The authors document a combination of psychosocial benefits such as self-confidence, self-esteem, higher energy levels and positive body image. It is important to note that these gains appear to be influenced by interactions with parents, who can either encourage or dampen a daughter’s interest and involvement. So, too, do persistent and narrow cultural prescriptions for appropriately “feminine” behavior erode the potential of physical activity and sport to enhance girls’ mental health. On the other end of the interdisciplinary spectrum, some of the biological and chemical processes associated with health and fitness concerns are also highlighted. And finally, two of the authors of this report, psychology of sport scholars Doreen Greenberg and Carole Oglesby, discuss the growing recognition among mental health professionals that exercise and sport can be effective treatment interventions for the significant number of girls who suffer from depression or anxiety disorders. Obesity The Surgeon General’s report on nutrition and health (Public Health Service, 1988) identified obesity as a major public health problem in the United States; subsequently, the Surgeon General’s report on physical activity and health (United States Department of Health and Human Services, 1996) identified physical inactivity as a serious public health problem nationwide. Aware of this concern, the authors of this report discuss a variety of factors associated with the rising rate of obesity among American adolescents. Social factors include the influence of television, dwindling requirements for physical education in the schools, and the steep sport dropout rate among adolescents. Related to physical health concerns, this report explores the physiological and epidemiological aspects of obesity such as the links between the development of hyperlipidemia, hypercholesterolemia, hypertension and diabetes, which in turn elevate risk for coronary heart disease. Finally, in her section on the psychological dimensions of participation, psychology of sport scholar Diane Wiese-Bjornstal stresses the need to help overweight or obese girls overcome social pressures and personal misgivings about physical activity so that they can become less sedentary. The Female Athlete Triad Several authors discuss the complex combination of psychological and physiological processes that operate in relation to the female athlete triad. In Section I, exercise physiologist Patty Freedson and psychology of sport scholar Linda Bunker document many physiological benefits of exercise and sport participation for girls such as potential gains in strength and aerobic power. It also appears promising that girls’ involvement in sport and exercise could effect increased immune functioning and the prevention of certain cancers in adult life. They also express their concerns about the “female athlete triad,” which refers to three interrelated health problems that are prevalent among some types of female athletes and some girls who engage in excessive exercise: eating disorders, exercise-induced amenorrhea and bone loss. Several authors demonstrate how these syndromes have complex psychological, physiological and social origins and profiles. For example, girls’ perceptions of their bodies are partly shaped by unrealistic media images that create false connections between a lean body type or “washboard abs” and subsequent success, sex appeal and self-mastery. The obsession with thinness can also be fed by a coach who demands weight loss from the athlete, or the desire to be attractive to boys and accepted by one’s peers. Because we are in the early stages of investigating this syndrome, the data we have are very limited. Female athletes most at risk should certainly be aware of the dangers, but we should not assume that the triad is limited to an athletic population (Lutter & Jaffee, 1996). Sport and Academic Achievement It is said that “the fish are the last ones to discover the ocean.” In Section III, Margaret Duncan illustrates how several research findings debunk the “dumb jock” stereotype that high school athletes perform poorly in the classroom. School administrators are often unaware of the positive interplay between high-school athletics and academic achievement as measured by grade point average, standardized achievement test scores, lowered risk for dropout and greater likelihood to attend college. On average, female athletes fare better academically than female nonathletes, though Caucasian and Hispanic female athletes are more apt to derive some direct educational gains than are their African- American counterparts (“Women’s Sports Foundation Report: Minorities in Sport,” 1989). Good physical and mental health are also correlates of academic performance and social adjustment. Hence, from an interdisciplinary perspective, it is likely that athletic participation is part of a mutually reinforcing array of physical, psychological and social processes that enhance the overall educational experiences and commitments of many girls. In summary, understanding the role of physical activity and sport in the life of the “complete girl” is a dauntingly complex agenda. The mosaic of interdisciplinary findings and interpretations assembled in this report will deepen both insight and resolve in this regard. POVERTY, RACE AND PHYSICAL ABILITY Girls from economically disadvantaged backgrounds, girls of color and girls with disabilities can face unique obstacles in relation to physical activity and sport. Poor families cannot afford to invest in health club memberships, exercise machines and equipment for their daughters. Families of color, who are disproportionately poor, often cannot pay user fees or transportation costs to bring daughters back and forth between home and school. Fitness and sport are often seen as unattainable luxuries rather than potential resources. Dual-worker parents or single parents (most often mothers) sometimes depend on older daughters to cook or care for smaller children after school, thus curbing their involvement with extracurricular activities. Poor or working-class girls often work part-time jobs to help families make ends meet, thereby reducing the amount of time and energy available for exercise or sports. Parental perceptions of the benefits of exercise and athletic participation for daughters also vary by race and class. For example, one national survey found that Caucasian parents more often mentioned health- related benefits, character benefits and social factors than did African-American parents (“The Wilson Report: Moms, Dads, Daughters and Sports,” 1988). Many of the problems girls of color experience in relation to physical activity and sport grow out of the same soil—poverty. Epidemiological research shows that exposure to violence, family fragmentation, substance abuse, sexually transmitted diseases and greater risk for unwanted sexual activity often share the common causality of poverty. Lack of physical activity and athletic opportunity can be added to this list. Economically disadvantaged girls of color are more likely to suffer from an unsafe and unhealthy environment. The simple act of walking or jogging may be problematic in neighborhoods where crime flourishes. Poor girls often do not have access to athletic resources, effective coaching and expert training. There is a lack of basic information about exercise, diet and sport. They are less apt to receive quality physical education and athletic training at earlier ages which, in turn, erodes the foundation for subsequent motor development. Because school and community athletic programs depend on tax dollars to thrive, capital flight from many urban areas is undermining the provision of adequate exercise and athletic opportunities for both minority girls and boys. The rising cost of liability insurance is also making it difficult for school districts, especially poorer ones, to provide quality athletic and intramural programs. Little is known about the dreams, interests and physical activities of girls of color. Although women of color are often more visible in sport media, and in certain sports like basketball and track and field, they are underrepresented in sports such as swimming and tennis (Abney & Richey, 1992). During the early 1980s, African-American and Hispanic adolescent females comprised about 4.4 percent and 3.2 percent of high school athletes respectively, compared to 29.1 percent of their Caucasian counterparts (Melnick, Sabo, & Vanfossen, 1992). There is also indirect evidence that African-American and other ethnic minority females are less physically active than Caucasian females (King et al., 1992; Pate et al., 1995). And finally, despite the accomplishments of the Special Olympics and Paralympics, few opportunities exist for emotionally or physically challenged adolescents to engage in exercise and sport. Differently-abled children are three times more likely to be sedentary than their able-bodied peers and the physical activity levels of children with disabilities drop precipitously during adolescence (Longmuir & Bar-Or, 1994). It should be noted that the authors of this report make only periodic references to socioeconomic status, race, ethnicity and physical disability. This is due not so much to choice, however, as to the fact that so little research has focused on these groups of girls. WHAT RESEARCHERS DON’T KNOW CAN HURT GIRLS This report is the first to assemble the bulk of existing research on girls’ involvement with physical activity and sport. However, because of the lack of available data and analysis, the authors of this report were unable to address in any depth some key aspects of girls’ experiences with physical activity and sport. Three emerging research concerns are briefly discussed below. Unwanted Sexual Behavior and Adolescent Pregnancy Adolescent pregnancy is a major social problem in the United States. Though the belief that sports can help many young girls avoid unwanted sexual behavior and pregnancy is widespread among coaches and athletes, precious little research has been done in this area (Sabo & Melnick, 1996). Two recent studies shed some initial empirical light on the hypothesized connections among exercise, athletics and adolescent girls’ sexual behavior. First, Brown, Ellis, Guerrina, Paxton and Poleno (1996) analyzed female adolescents’ responses to the United States Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention (1995) survey, “Health Risk Behavior for the Nation’s Youth.” The researchers found that the more days adolescent females exercised per week, the more likely they were to postpone their first experience with sexual intercourse. Second, preliminary analysis from a study of adolescents from western New York (an area with one of the highest rates of adolescent pregnancy in the United States) indicated that higher rates of athletic participation among adolescent females were significantly associated with lower rates of both sexual activity and pregnancy (Sabo, Farrell, Melnick, & Barnes, 1996). Sexual Harassment Sexual harassment is experienced by approximately 31 percent of female high school students (American Association of University Women Educational Foundation [AAUW], 1993). Sport scholars have recently begun to study the prevalence and social-psychological dynamics of sexual harassment in athletic settings (Sabo & Oglesby, 1995). Many key questions need to be addressed. For example, how do female athletes perceive and react to sexual harassment from boys and adults? Do higher self-esteem and physical prowess fostered by sports help females to be more assertive with inappropriately invasive males than their non-athletic counterparts? Additional research needs to be done on the ways that athletic participation may empower girls to more effectively cope with sexually hostile situations. Exercise and Sport as a Family Asset Regretfully, little research has focused on the ways that exercise and sport promote interaction and insight between parents and children. As is the case with sexual harassment, many important questions in this area remain unanswered. Do parents look to sport to provide after-school activities that keep daughters physically active, socially engaged and off the streets? To what extent do physical activity and sport help parents nurture moral development and values in their children? In what ways can parents effectively encourage their daughters’ involvement with physical activity and sport? Clearly, more investigation of the interdependencies among physical activity, sport, families and schools is needed. CONCLUSION: EXPANDING THE RESOURCE This report will fuel the growing awareness that physical activity and sport are enormously important in the lives of girls. Perhaps this message is being sent by girls themselves who are, as the saying goes, “voting with their feet,” and entering the realms of fitness and sport in vastly increasing numbers. In contrast to the nineteenth century naysayers who decried strenuous exercise and athletic participation for women as dangerous and unladylike, today, educators and public health advocates recognize the overall benefits for girls’ physical health and emotional well-being. As health care costs continue to escalate, and pressures on the American health care system to provide quality care intensify, the logic of preventive health strategies that involve physical activity and sport becomes economically salient. The overall vision that emerges from this report frames physical activity as a developmental aid and public health asset for girls and, by inference, for boys as well. Physical activity can serve as a social and cultural intersection where adolescents, parents and caring adults can come together in mutually supportive ways. The aerobics class, fitness run or basketball court are safety zones where young girls can hang out together, test and challenge themselves, learn about competition, develop physical fitness components such as cardiovascular endurance, strength and flexibility, and have fun all at the same time. The real and potential benefits that physical activity and sport have to offer girls, their families and communities, however, continue to be stymied by several factors. Economic and cultural barriers block wider participation, especially for poor girls and girls of color. Despite increasing interest and participation rates, physical activity and sport remain underutilized resources for the many girls who are mired by sedentary lifestyles or dissuaded from getting involved because of gender stereotypes, discriminatory practices and lack of opportunity. There are also appreciable numbers of girls for whom athletic participation is associated with illness, injury and addiction to exercise rather than with physical and mental well-being. And finally, there needs to be more systematic research on the numerous ways that physical activity and sport influence girls’ lives. Simply put, too little research has been done in an area where girls have too much to gain. For this reason, each of the authors has listed priorities for future research at the end of their respective sections. This report concludes with a list of policy recommendations. The information and analyses gathered here hold implications for parents, educators, coaches, athletic administrators, public health officials and lawmakers. There is more at stake in the struggle to expand girls’ physical abilities and athletic opportunities than learning to do jumping jacks or winning and losing games. Future policy decisions need to be grounded in the broader understanding that girls’ involvement with physical activity and sport is just as much about physical vitality, emotional well-being, community health and educational opportunity as it is about who runs the farthest or scores the most points.
Physiological Dimensions PATTY FREEDSON, PH.D., UNIVERSITY OF MASSACHUSETTS—AMHERST LINDA K. BUNKER, PH.D., UNIVERSITY OF VIRGINIAMUCH IS KNOWN FROM RESEARCH ON THE EFFECTS OF EXERCISE and sport participation on adolescents and adults. However, the majority of this research was conducted on males, or focused on comparisons between boys and girls, with little research focusing exclusively on females. The present review must therefore include research on adults and males, as well as the biophysical effects of physical activity and sport on girls and the potential impact of these experiences on their maturation and adult lives. The acquisition of fundamental motor proficiency, which is directly linked to physical activity, is an important goal for early childhood. Not only must children learn to control their bodies in space, they also need to acquire the fundamental skills which will aid daily living, vocational pursuits and recreational/leisure activities. These skills are interdependent with health-related physical fitness and must be considered in any discussion of the biophysical effects of physical activity on girls. It is important that activities in childhood include both the motor and health aspects of physical fitness. Both health-related fitness and motor skill development are important because: (a) children need a reasonable level of motor skill proficiency to participate in activities that build endurance, power and strength, and (b) they need reasonable levels of fitness to engage in exercise and sport activities which will provide them with physical activity as adults. Recognizing the need for both motor skill development and adequate fitness is critical because the benefit of lifetime participation in physical activity has an impact on psychological aspects (see also Section II: Psychological Dimensions), social aspects (see also Section III: Sociological Dimensions) and the mental health of young girls and women (see also Section IV: Mental Health Dimensions). The simultaneous acquisition of both motor and physical fitness begins in early childhood, as children use movement as their mechanism to learn about their world. It continues in school where all children should participate in daily physical education activities which set both the pattern of physical activity and the fundamental skills to be successful and happy when participating. Physical activity has long been recognized for its effects on the maturing child. However, one of the challenges of interpreting research on children is the difficulty of differentiating between the changes in physiological functioning which may be affected by regular exercise or strenuous training, and those effects which are the natural result of maturation. This problem is compounded by the traditional use of control groups to help differentiate between the effects of the exercise intervention and those of normal growth and development, because most children are already quite active (Bar-Or, 1989). This makes the experimental designs more complicated, the exercise interventions more intensive than those which would be adequate for adult participants, and the interpretation of the data more challenging for the researcher. The biophysical changes which result from exercise and training may shift in the same direction as those which occur due to maturation, or they may change in the opposite direction. For example, peak anaerobic power increases due to both maturation and physical training. Similarly, decreases in oxygen cost of moving are also caused by both maturation and physical training. With respect to biophysical changes in the opposite direction, the body’s ability to use oxygen (i.e., anaerobic threshold, percent V. O2 max) decreases due to maturation but increases as a result of training (Bar-Or & Malina, 1995). It is possible to consider the known effects of physical activity in many different ways. The following information clusters the research into three categories related to biophysical considerations: benefits for girls, potential deleterious effects and potential long-term effects related to disease prevention and quality of life. BENEFITS OF PHYSICAL ACTIVITY FOR GIRLS Research on the biophysical impact of exercise on children and adolescents is quite extensive although, as previously mentioned, investigations focusing exclusively on girls is limited. The following information addresses those benefits specifically relevant to girls. We focus in particular on benefits related to power (i.e., aerobic power or endurance and anaerobic power), strength, weight management and health-related issues such as immune function effects and reproductive maturation. Strength Muscular strength is defined as the ability to generate force and includes dynamic or isotonic strength (i.e., the ability to generate force through a range of motion) and isometric strength (i.e., the ability to generate force at a single point in the range of motion where muscle length does not change). With respect to the maturing female, girls grow stronger as they mature, making it difficult to assess whether changes are the result of maturation or physical activity levels. However, several studies have found that short-term training programs can produce increases in muscle strength in children (Grodjinovsky & Bar- Or, 1984; Sale, 1989). Pfeiffer and Francis (1986) have suggested that the relative gain in strength due to exercise is similar for all children, whether they be prepubescent, pubescent or postpubescent. According to Malina and Beunen (1996), “prepubescent” is defined as the absence of development of secondary sex characteristics, “pubescent” is initial and continued development of secondary sex characteristics, and “postpubescent” is adult or mature state of development for secondary sex characteristics. Increases in physical activity and short-term training programs can produce positive changes in several forms of “strength-related” factors, including anaerobic power and muscle endurance. Maturation-related strength increases at a linear rate for most girls up until about age 14. Beyond that point, the rate of increase slows and for sedentary girls may actually decrease (Blimkie, 1989; Parker, Round, Sacco, & Jones, 1990). However, systematic physical activity can produce marked improvement in strength for girls, probably due to the improvement in motor unit activation and coordination (Sewall & Micheli, 1986; Wilmore, 1974). Power The concept of power is related to the capacity to do work per unit time and is directly related to both muscular strength and cardiovascular functioning. The following discussion of power includes both aerobic power which is necessary for endurance activities and anaerobic power which is necessary for short-term, high-energy– demanding activities. Aerobic Power and Endurance Performance Cardiorespiratory fitness represents the maximal transport of oxygen, which is a function of the product of heart-rate and stroke volume (i.e., cardiac output), the oxygen-carrying capacity of the blood (i.e., hemoglobin content) and the maximal arterio-venous oxygen difference. Aerobic power is typically measured by V. O2 max as determined by either cycle ergometry or treadmill exercise. Expressed as an absolute measure (l • min-1) or as relative to body mass (ml • kg-1 • min-1), measurements of aerobic power are extremely reliable in both children and adults if standard criteria defining maximal responses are used and if subjects—children and adults—participate with maximum effort. The general pattern of change in absolute aerobic power (l • min-1) for girls suggests that it increases with growth prior to adolescence, but in the absence of systematic exercise, it steadily declines into adulthood. Summarizing cross-sectional data from several studies testing children of different ages, Armstrong and Weisman (1994) reported a decrease in absolute aerobic power in adolescent girls 13 to 15 years of age. Despite the apparent decrease in absolute aerobic power in females ages 13 to 15, the overall rate of increase in treadmill absolute aerobic power for females between the ages of eight and 16 was approximately 12l • yr-1. Examination of treadmill-relative aerobic power across age revealed a steady decline for females (Armstrong & Weisman, 1994). Aerobic power relative to body mass (i.e., V. O2 max expressed as ml • kg-1 • min-1) averaged 50ml • kg-1 • min-1 for girls at eight years of age which decreased to approximately 40ml • kg-1 • min-1 by age 16. This trend was not observed for males across the same age span; they maintained a relatively stable aerobic power of approximately 55ml • kg-1 • min-1 (Armstrong & Weisman, 1994). This decrease in aerobic power is most apparent at the time of puberty when there is an increase in body fat. Additionally, cross-sectional data indicate that inactive children have lower V.O2 max than normally or highly active children (Malina & Bouchard, 1991). Fortunately, this decline in aerobic power can be reversed with aerobic training (Rowland, 1989). Both short-term and long-term training programs seem to result in about the same improvements in maximal aerobic power among sedentary older children and adults (Bar-Or & Malina, 1995; Pate & Ward, 1990). Aerobic power and endurance performance are closely related in adults, but seem to be dissociated in adolescents. Specific to adolescent females, aerobic power expressed relative to body mass declines through normal growth and development, yet endurance performance (e.g., timed mile run) improves. For example, time to complete a one-mile run improves by approximately 15 percent in females between eight and 17 years of age, despite a 20 percent decrease in relative aerobic power (Rowland, 1989). Nonetheless, it should be pointed out that regular exercise can increase oxygen uptake and diminish some of the decline that would otherwise occur. Improvements in running economy that occur with maturation most likely explain the dissociation between aerobic power and endurance performance in adolescence. Anaerobic Power Anaerobic power, or the capacity to perform strenuous activities in short bursts of time, does not rely as extensively on the cardiovascular system. For most girls, anaerobic power (such as that required to do a vertical jump) increases throughout early childhood, but decreases in adolescence and young adulthood. However, anaerobic power improves in children who exercise, especially those who train systematically. Gains as a result of training for adolescents (10 to 13 years) range up to about 20 percent. Weight Management Juvenile obesity is “arguably the most prevalent chronic illness among children in North America and represents an immense public health challenge” (Bar-Or & Malina, 1995, p. 110). A child is considered obese when his or her weight-height ratio is 20 percent or more above the upper limit of the desirable weight as assessed by primary care physicians and pediatricians using standard growth charts (Insel & Roth, 1991). According to data from the National Center for Health Statistics (1991), approximately twice as many children are overweight today compared to children in the 1960s (Blair et al., 1996). It should be noted that juvenile obesity is particularly prevalent in girls from highly urbanized areas (Dietz & Gortmaker, 1984), some ethnic groups (e.g., Hispanic Americans, Pima Indians [King & Tribble, 1990]) and those with disabilities (Dietz, 1995). Problems with weight control occur when the caloric intake does not match the caloric expenditure. Though the major problem for obese individuals may be the nature of the calories consumed (especially excess fat intake in terms of the percent of the total calories), exercise is an important adjunct in weight control for high-school girls (Wells, 1991; Moody, Wilmore, Girandola, & Royce, 1972) and for women 18 and over (Miller, Lindeman, Wallace, & Niederpruem, 1990). Exercise has the effect of increasing caloric expenditure, and also seems to protect fat-free mass while promoting the loss of fat mass (King & Tribble, 1990). For the general population of girls, their daily routine provides an adequate balance of physical activity and caloric intake. However, to assist the obese child, it is essential that a multidisciplinary program include nutrition education and increased physical activity both during weight loss and afterward. Many of these programs are provided in physical education programs within our schools and, as Ward and Bar-Or (1986) have suggested, this is the most practical way to combat this national problem. Vogel (1986) presented an extensive review of physical education programs and concluded that daily programs can produce changes in body composition (i.e., percent lean versus fat mass), aerobic fitness, balance, endurance performance and lipoprotein profiles (especially for children with elevated lipoproteins). In addition, when programs are designed to promote motor skills and aerobic fitness, changes in skinfold thickness may occur (Simons-Morton, Parcel, & O’Hara, 1988). The key to controlling obesity is a combination of caloric reduction and increasing caloric expenditure. However, when controlling obesity, one must keep in mind the concurrent need to support the growth process and to maintain nutritional adequacy. Immune System The relationship between immune function and physical activity must be discussed in relation to the intensity of the activity (Liesen & Uhlenbruck, 1992). A great deal of research reports that low- to moderate-intensity training enhances immune function with increases in levels of interleukin-1 and interferon and increased numbers of natural killer cells, circulating lymphocytes, granulocytes, monocytes and phagocytic macrophages (Kramer & Wells, 1996). However, with exhaustive or very intense and prolonged training, there may be a depression of immunological function. Overtraining may depress the levels of immunoglobulin in blood and saliva, reduce the responsiveness of T-lymphocytes to antibody synthesis and increase the risk of infectious and viral diseases (Newsholme & Parry- Billings, 1994). The T-lymphocytes and natural killer cells seem to function as a tumor inhibitor to retard the growth of cells which have been genetically damaged (i.e., cancer). Similarly, monocyte and macrophage function also decreases the likelihood that aberrant cells will be facilitated or that metastases will occur. Thus it appears that moderate intensity exercise may have a positive effect in retarding diseases such as cancer or those caused by viruses such as colds or influenza (Newsholme & Parry-Billings, l994). See the section below entitled “Potential Long-Term Effects” for a more detailed discussion of this topic. Research on the effects of exercise on the immune system is mixed, depending on both age and intensity of physical activity. There is some evidence that increased physical activity produces moderate immune response suppression, but the clinical importance of this response is debatable (Calabrese, 1990). For example, adolescent athletes have been found to be more susceptible to infections than nonathletes (Shephard, 1984), but this may also be true for other children who participate in group activities in close proximity to one another (e.g., band, drama). In contrast, in a prospective study, Osterback and Ovarnberg (1987) found no difference in immune function between 12 year-old athletes and nonathletes. Reproductive Functioning: Menarche There are many anecdotal reports of the positive influence of regular physical activity on the menstrual cycles of pubescent girls. Many girls report less physical distress associated with the cycle and increased periodicity (i.e., regularity) when moderate physical activity is part of their lifestyle. For many years it was believed that delayed onset of the menstrual cycle (i.e., menarche) was the result of sports participation by young female athletes. This conclusion was based on the observation that menarche occurred later in athletes than nonathletes. An alternative explanation was offered by Malina (1983) who suggested that young females who mature early are socialized away from sports participation. For the young female athlete, late maturation accompanied by delayed fat deposition favors athletic success and may result in a type of self-selection. In other words, delayed menarche may result in continued participation in competitive sport (Stager, Wigglesworth, & Hatler, 1990). Wells (1991) summarized data from several studies and reported the age of menarche for girls participating at different competitive levels: nonathletes = 12.29 years, athletes = 13.02 years, college athletes = 13.05 years, national-level track and field athletes = 13.58 years, Olympic athletes (Montreal) = 13.66 years, national-level middle-distance runners = 14.10 years, Olympic volleyball athletes = 14.18 years and national-level runners = 14.20 years. It should be noted that these data were collected retrospectively and may be influenced by recall bias in which athletes remember later menarche. Delayed menarche is a particularly complex issue which could have both positive and negative consequences. Historically, delayed menarche, which is often found in female athletes who train at high levels, was viewed as a problem because it supposedly compromised fertility (Frisch, Wyshak, & Vincent, 1980). More recently, concern about delayed menarche has focused on its impact on peak bone density. Menarche is associated with an increase in circulating levels of estrogen. Estrogen is a necessary hormonal trigger for increasing bone density in adolescence and maintaining bone density in the mature female. Studies have reported that early menarche is associated with increased bone density (Fehily, Coles, Evans, & Elwood, 1992; Johnell & Nilsson, 1984). Research examining the relationship between delayed menarche in athletic females and bone density is lacking. Nevertheless, it is possible that delayed menarche and/or amenorrhea with their associated reduced circulating estrogen may result in reduced peak bone mass and increased risk of osteoporosis in later life because the available time for laying down bone is reduced (Wells, l991). This concern seems to be greatest for females who train at very high levels and who may experience both delayed menarche and amenorrhea. On the other hand, delayed menarche may be of some positive significance because the early onset of menarche has been linked with increased risk for breast cancer (Doll & Peto, 1981). Participation in regular exercise or sport may also reduce the likelihood of childhood obesity, which often produces earlier onset of menarche. See sections below entitled “Amenorrhea” and “Cancer.” POTENTIAL DELETERIOUS EFFECTS OF PHYSICAL ACTIVITY ON GIRLS In general, moderate to strenuous physical activity poses few risks to the healthy girl and, when deleterious effects do occur, they seem to involve the musculoskeletal system. Benefits to cardiovascular functioning seem to be unanimously supported, with no known evidence to suggest detrimental effects (Nudel et al., 1989). There is, however, growing evidence to suggest that we should be concerned for girls who are training at the elite level, primarily because of overuse injuries and changes in reproductive system maturation and functioning. Three of these concerns—osteoporosis, amenorrhea and disordered eating—have sometimes been lumped together and described as the “Female Athlete Triad.” The foundation for these problems is that there is often a preoccupation with body weight and composition among female athletes. This may lead to undereating and overexercise and underconsumption of calories which together produce undesirable health-related consequences. It should be noted that this is not a problem unique to girls, but one which is also found in boys who participate in such activities as gymnastics, ice skating and wrestling (Hui, 1995). Injuries Increased levels of physical activity and sport participation are bound to produce increases in injuries. Many of these injuries are caused by inappropriate grouping of children based solely on age, without respect to maturation, weight or skill level. When children are grouped by chronological age, the smaller, less mature individual may be forced to compete against a more mature individual who is larger, stronger and faster. Similarly, increased participation in competitive sport for children may necessitate making a distinction between injuries caused by physical contact or purposeful intent (e.g., sliding into second base to break up a double play), versus those that occur as routine injuries (e.g., a sprained ankle). Differences in maturation and in the child’s purpose of participation—as well as intensity/seriousness of training and competition—may present the potential for decreased performance and physical harm. All of these factors may discourage children from participating. Injuries may also be caused by inappropriate levels of strength and flexibility needed for particular activities. Through appropriate educational programs generally provided in school physical education, children and coaches/teachers should learn appropriate techniques for proper warm-up, stretching and physical conditioning. Amenorrhea Some young women experience irregular or interrupted menstrual cycles which have been associated with excessive exercise. It is not clear whether this is a benefit (in relation to reduced estrogen- dependent cancers due to fewer ovulatory cycles) or a liability (in relation to such outcomes as lower bone density). The etiology of amenorrhea (i.e., interrupted menstrual cycle) may not simply be a high level of energy expended in exercise, but may also be related to energy imbalance, which is a function of both energy intake and energy expenditure (Loucks & Heath, 1994; Wakat, Sweeney, & Rogol, 1982). This concept is supported by studies that have shown normal reproductive function even with increased exercise energy expenditure when caloric intake was not limited (Rogol et al., 1992). Strenuous physical training may produce ovulatory dysfunction and shortened luteal phases of the menstrual cycle, perhaps combined with a prolonged follicular phase (Loucks, Vaitukaitis, & Cameron, 1992). One explanation for this is the activity of the hypothalamic-pituitary-adrenocortical axis which may depress the hypothalamic GnRH pulse generator (Kramer & Wells, 1996). A potential negative consequence of excessive physical activity accompanied by persistent reduced estrogen levels may be lower bone density, often linked to amenorrhea and osteoporosis. Female athletes who are amenorrheic or oligomenorrheic (i.e., irregular cycles) have been found to have lower bone densities than the general population (Drinkwater et al., 1984; Myburgh, Bachrach, Lewis, Kent, & Marcus, 1993; Rencken, Drinkwater, & Chesnut, 1993). Disordered Eating Much has been written about the problems of disordered eating in elite female athletes or those who train at extreme levels. The pressures to maintain the so-called “ideal physique” may produce dysfunctional eating habits and result in body fat levels which drop too low (Steen, 1991; Wilmore, 1974). The negative health consequences of anorexia and bulimia (i.e., bingeing on food then purging) are great and deserve attention, but it is important to realize that this is not a problem which is “caused” by exercise, but rather by psychological issues in the life of girls (see also Section II: Psychological Dimensions, on the psychological effects of exercise on girls). Female athletes who participate in sports where body weight and appearance are considered to be essential components for optimal performance (e.g., distance runners, figure skaters, gymnasts and dancers) are particularly vulnerable to this problem (Montgomery, 1991). A survey by Rosen and Hough (1988) indicated that one hundred percent of gymnasts studied were on a diet, 62 percent were using a method of weight control that was extreme, and 75 percent were told by their coaches that they had to lose weight. Similar observations have been reported in ballet dancers (Braisted, Mellin, Gong, & Irwin, 1985). Although data are lacking, it seems reasonable to conclude that adolescent female athletes involved in sports where weight and body fat are predictors of successful performance, have an increased risk for developing disordered eating patterns. In addition, it should be noted that the presence of disordered eating is not only seen in elite-level athletes but also among young girls who strive to be elite-level performers. Young athletes who are not particularly successful in sport may also be susceptible to this problem as they see dietary practices as something they can control and use to please their coach or parent despite the fact that high level performance is not possible. POTENTIAL LONG-TERM EFFECTS OF PHYSICAL ACTIVITY Children grow into adulthood with the body they have lived with and nurtured or abused while growing up. Much of the early support for physical activity for children focused on the advantages of adequate strength and flexibility in the prevention of low-back pain and the importance of regular physical activity to prevent obesity. However, in recent years, the focus has expanded to include the positive effects of physical activity on chronic diseases, some of which often begin in childhood and adolescence and may later manifest in adulthood (e.g., cancer, diabetes, osteoporosis, heart disease) (Després, Bouchard, & Malina, 1990). Moderate to high levels of physical activity, and the consequent increase in health-related fitness, are important for children for at least three reasons: (a) they may lead to a habit of physical activity which may carry over to adulthood; (b) they may contribute to overall health status in later life; and (c) they may have a preventive function in some adult diseases. As Bar-Or and Malina (1995) have suggested, there are at least two reasons for encouraging active lifestyles in girls:
Coronary Heart Disease It was noted in the recent Surgeon General’s Report on Physical Activity and Health (U.S. Department of Health and Human Services, 1996) that, in the United States, coronary heart disease has a higher mortality rate than all types of cancer combined. The disease is thought to begin in childhood and results in atherosclerotic plaques lining the arteries of the heart and reducing blood flow and oxygen delivery to the heart. The primary pathology associated with coronary heart disease (CHD) is atherosclerosis, which is linked to elevated blood cholesterol levels and hypertension. There appears to be a direct link between CHD and elevated levels of total cholesterol, low-density lipoprotein cholesterol (LDL), very-low- density lipoprotein cholesterol (VLDL) and low levels of high-density lipoprotein cholesterol (HDL) (National Cholesterol Education Program [NCEP], 1991). Children who have higher than average levels of body fat reportedly have a greater risk for elevated blood pressure, total cholesterol and LDL cholesterol (Williams et al., 1992). The link here is dramatic, because children who have high levels of cholesterol are almost three times more likely than other children to have high cholesterol levels as adults (NCEP, 1991). In a major review article examining relationships among physical activity, nutrition and chronic disease, Blair et al. (1996) found that the best strategies for lowering cholesterol levels appear to be a combination of diet and exercise. These authors also discovered that exercise may be beneficial because it lowered blood pressure, perhaps through decreased cardiac output and decreased peripheral resistance, and exercise may also reduce the risk of thrombosis because of positive effects on blood clotting. It is important to note that this major review examined studies which sampled males and females across the lifespan. Cancer The link between cancer and exercise is probably intimately related to diet and body composition. Obesity is associated with an increased risk for endometrial and gall-bladder cancers in women and the magnitude of excess weight is also related to breast cancer in postmenopausal women (Kimm & Kwiterovich, 1995). Though little evidence exists that the physical activity of girls directly affects such cancers, it is likely that establishing a habit of regular exercise may continue into adulthood and aid in the maintenance of appropriate weight. Few studies have been done that are prospective or that begin with younger women. One exception is a case-control study by Bernstein, Ross and Henderson (1992). These authors reported that with respect to cancer, a strong link exists between exercise and menstrual cycles. The authors also state that for every year that menarche is delayed, breast cancer is reduced five to 15 percent. Finally, these authors found that women who start menstruating at an early age, and establish regular cycles quickly, have a higher risk of cancer than those with later menarche or irregular cycles. This is a particularly salient finding because later onset of menarche and/or irregular cycles are typical of girls who participate in high levels of training associated with interscholastic or intercollegiate athletics. One promising development is that estrogen-dependent cancers (breast, endometrial and ovarian) may be less prevalent in women who exercise regularly, especially those for whom exercise is part of their occupation. Kramer and Wells (1996) have postulated four mechanisms which might account for the preventive effects of exercise on these cancers:
Another link to physical activity and reduced cancer may be the effect of serious training on menarche. Research has suggested that the risk of breast cancer is reduced up to 15 percent for each later year of age at menarche (Hsieh, Trichopoulos, Katsouyanni, & Yuasa, 1990). Women whose natural menopause occurs before age 35 have been found to have a decreased incidence of breast cancer, while those with natural menopause after age 55 have an increased incidence. This may suggest an association between the cumulative number of ovulatory menstrual cycles and estrogen-dependent breast cancer (Kampert, Whitemore, & Paffenbarger, 1988). If this is true, an increase in physical activity during adolescence may be an ideal nonhormonal approach to decrease the number of lifetime ovulatory cycles and reduce exposure to estrogen (Bernstein et al., 1992). Diabetes Mellitus Diabetes mellitus is one of the ten most prevalent causes of death in the United States (Blair et al., 1996). Many of the debilitating effects of diabetes are associated with the increased risk of heart disease and hypertension. Developing the habit of exercise as a child may help to maintain activity levels into adulthood. Noninsulin dependent diabetes (NIDDM), “known as the insulin-resistance/ hyperinsulinemia syndrome” (Blair et al., 1996, p. 336), often occurs with other problems such as hypertension, hyperlipidemia and atherosclerosis. Regular exercise is important in both the prevention and management of NIDDM by increasing glucose transporter concentration and disposal and by increasing insulin sensitivity and lowering plasma insulin concentrations (Horton, 1986). Women who participate in vigorous exercise at least once per week have shown a reduced risk of NIDDM (Manson et al., 1991), while children (both obese and lean) have better glucose control in response to regular exercise (Zierath & Wallberg-Henriksson, 1992). Osteoporosis and General Bone Health The decrease in bone mass that accompanies the aging process and the loss of estrogen levels after menopause often results in osteoporosis. The risk factors associated with osteoporosis include age, race, height-to-weight ratio and menopause in women. The three most important factors that contribute to healthy bones appear to be hormonal, nutritional and mechanical (Blair et al., 1996). Because there is no cure for this condition once it occurs, efforts must focus on prevention. In young childhood and adolescence, the development of peak bone mass is directly affected by regular physical activity combined with adequate calcium and vitamin D intake. Greater bone mass develops due to weight bearing, which is most often experienced during physical activity, and helps to protect against osteoporosis later in life when bone loss occurs. In fact, it is essential to place demands on bone for it to remain healthy. For example, a young adult at bed-rest for one week will lose about one percent of spinal density, which could take up to four months to regain (Krolner & Toft, 1983). In contrast, it has been found that young tennis players have higher bone density in their preferred (racket holding arm) than in their other arm, thus supporting the positive role of placing demands on bone (Jacobson, Beaver, Grubb, Taft, & Talmage, 1984). In order for bones to grow properly, it is important for children, particularly adolescents, to participate in regular (preferably daily) physical activity (Kimm & Kwiterovich, 1995). The growth and development of children should also be monitored in terms of optimal weight and the balance of strength and flexibility. Because weight is linked to spinal bone density, it is critical to monitor underweight children carefully. In particular, any adolescent female who is very lean, has an eating disorder or has amenorrhea should be considered at high risk for osteoporosis (Ponder et al., 1990). The interrelationships among such chronic diseases as diabetes, coronary heart disease and stroke argue for a greater need to maintain appropriate weight levels based on one’s age, body size and structure. At the same time, caution should be used in overtraining as bone-mineral density may be compromised, especially when linked to amenorrhea. CONCLUSIONS AND RECOMMENDATIONS Physical activity, which includes the opportunity to develop an active lifestyle, to be physically fit and to acquire fundamental motor skills, can positively impact the overall health of girls in several ways. For example, increased fitness levels can contribute to better posture, the reduction of back pain and the development of adequate strength and flexibility, qualities which allow girls to participate fully in their daily activities, both vocational and recreational. The information presented below represents a summary of the contributions of sport and physical activity to the health and fitness of girls, as well as some recommendations for ensuring that all girls benefit from such involvement.
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