Skeletal growth reaches its peak at an earlier age in girls (10.5 to 13 years of age) than in boys (12.5 to 15 years of age). Skeletal maturity occurs by the age of 17 to 19 years in girls, and by the age of 21 to 22 years in boys.

The female pelvis is wider than the male pelvis, causing an increased quadriceps (Q) angle, which commonly contributes to anterior knee pain (also called “patellofemoral syndrome”).

Women develop thinner, lighter bones than do men, which may predispose them to osteoporosis and stress fractures.

In general, women have approximately 10% more body fat than men do, and 60% to 85% of the total muscle cross-sectional area of men. Because muscle is more metabolically active than fat, women have, on average, a resting metabolic rate that is 5% to 10% lower than that of men.

In response to weight training, women experience similar relative increases in strength as in men. Because muscle hypertrophy depends on hormones, as well as on training program type and volume, levels vary for each athlete. However, male athletes have greater absolute strength and muscle hypertrophy (owing to their hormonal environment) than female athletes have. Even with training, women have 30% to 50% less upper body strength than men have.

The percentage of body fat can be estimated by a variety of methods; ideal body fat composition varies with age and sex. Efforts have been made to establish a healthy minimum body fat percentage, but factors vary in women. However, athletes with a body fat percentage below 15% should be examined for any indications of the female athlete triad.

Women have a smaller thoracic cage and heart size, resulting in lower lung capacity and maximal cardiac output.

Maximum oxygen composition (Vo₂ max) is lower in women, largely because of differences in body composition and oxygen-carrying capacity. Vo₂ max is similar in boys and girls before puberty.

Women have a smaller blood volume, smaller iron stores, and lower concentrations of hemoglobin. These factors are associated with a lower oxygen-carrying capacity and they also increase the risk for anemia.

Both male and female elite athletes tend to have lower levels of hemoglobin than their sedentary counterparts. This may be secondary to both a low dietary intake and exercise-related blood loss, such as that which occurs from the gastrointestinal tract.

There is no evidence that the phase of the menstrual cycle influences athletic performance.

Female athletes may experience a wide array of alterations in the menstrual cycle, ranging from suppression of the luteal phase to amenorrhea. The latter is especially prevalent in athletes at risk for the “female athlete triad.”

Pregnancy results in many physiologic changes, including increases in cardiac output, in blood volume, and in oxygen demand. The American College of Obstetrics and Gynecology (ACOG) recently revised guidelines regarding exercise and pregnancy. The ACOG indicated that recreational and competitive female athletes with uncomplicated pregnancies can remain active, but those who exercise strenuously should seek close medical supervision. Athletes with a history of or risk for preterm labor or fetal growth restriction are advised to reduce physical activity in the second and third trimesters. Recent research also indicates that certain types of activities, such as diving (owing to changes in pressure underwater), exercise in the supine position (owing to restriction in large blood vessels), and any activity associated with risk for blunt abdominal trauma (contact sports and skiing) should be limited and/or avoided during pregnancy.

The female athlete triad refers to the inter-relatedness of three conditions: disordered eating, amenorrhea, and osteoporosis.

Traditionally, female athletes whose activity emphasized leanness for aesthetic reasons (ballet and gymnastics), who associated low body weight with improved performance (distance running), and those who were classified by weight (rowing and judo) were the ones thought to be at risk. However, women at risk have been found in many other sports, including swimming, soccer, volleyball, and cycling, and also in health clubs.

It is important that the clinician differentiates disordered eating from the eating disorders of anorexia nervosa and bulimia nervosa, which are psychiatric diagnoses with specific diagnostic criteria. Disordered eating is a much more common phenomenon, and restricting awareness to the extremes of anorexia and bulimia will result in failure to recognize girls at risk for the triad.

Disordered eating behaviors include the following:

Girls with eating disorders are often

Primary amenorrhea is defined as the absence of menarche by the age of 16 years.

Secondary amenorrhea is the absence of three to six consecutive menstrual cycles in women who have experienced menarche.

It is believed that exercise in the setting of inadequate calorie consumption may contribute to an “energy-deficient” state, which may lead to amenorrhea.

In this setting, amenorrhea represents a hypoestrogenic state, which can predispose one to osteoporosis.

Exercise-related amenorrhea is a diagnosis of exclusion. Other causes of amenorrhea (such as pregnancy) must be considered before it is assumed that cessation of menses in an athlete is exercise-driven.

Osteoporosis refers to bone loss in addition to inadequate bone formation, which results in lower bone mass, increased skeletal frailty, and increased risk of fracture.