chapter 18 Sex Differences in Sport and Exercise

Did You Know . . . ? Performance differences between men and women likely result from biological differences as well as social and cultural restrictions placed on females during their development and the fact that, historically, fewer women have competed in athletic events than men.

Body Size and Composition Major differences between boys and girls do not occur until puberty. Puberty in girls—estrogen causes pelvis broadening, breast development, fat deposition in hips and thighs, and increased bone growth. Puberty in boys—testosterone causes increased bone formation and muscle mass. After puberty, girls’ average relative body fat is 6% to 10% greater than that of boys.

Changes in Blood Concentrations of Testosterone and Estrogen From Birth to Adulthood Reprinted, by permission, from R.M. Malina, C. Bouchard, and O. Bar-Or, 2004, Growth, maturation, and physical activity, 2nd ed. (Champaign, IL: Human Kinetics), 414.

How Fat Is Stored Estrogen increases activity of lipoprotein lipase, which is produced by fat cells. Lipoprotein lipase is bound to walls of capillaries. Chylomicrons—major transporter of triglycerides—pass by in the blood. Lipoprotein lipase traps chylomicrons and transports them to fat cells. A decrease in lipolytic activity at the sites of fat storage makes it difficult to lose fat.

Neuromuscular Responses in Women Innate qualities of muscle and motor control are similar. For the same amount of muscle, strength is similar. Muscle fiber cross-sectional areas are smaller and muscle mass is less. More muscle mass is distributed below the waist. Upper-body strength expressed relative to body weight or fat-free mass is less.

No Sex Differences Are Seen When Strength Is Expressed per Unit of Muscle Cross-Sectional Area Reprinted, by permission, from P. Schantz et al., 1983, "Muscle fibre type distribution, muscle cross-sectional area and maximal voluntary strength in humans," Acta Physiologica Scandinavica 117: 219-226.

Distribution of Type I Fibers in the Vastus Lateralis Muscle in Male and Female Runners Adapted, by permission, from B. Saltin et al., 1977, “Fiber types and metabolic potentials of skeletal muscles in sedentary man and endurance runners,” Annals of the New York Academy of Sciences 301: 3-29.

Cardiovascular Responses in Women Higher heart rate response for absolute levels of submaximal exercise. Same HRmax and Q submaximal levels Lower SV due to smaller heart size and blood volume Less potential for increasing (a-v)O2 diff Lower hemoglobin content . -

Comparison of Submaximal Heart Rate (HR), Stroke Volume (SV), and Cardiac Output (Q) Between Men and Women . Data from HERITAGE Family Study, 2001.

Respiratory Responses in Women Differences in response mostly due to differences in body size More frequent breathing at maximal power output Smaller tidal volume Smaller ventilatory volume

Differences in Maximal Ventilatory Volumes With Age in Untrained (UT) and Trained (TR) Females and Males

Metabolic Responses in Women . Average VO2max after puberty is 70% versus average man’s 75%. More sex-specific essential body fat Lower hemoglobin levels Lower Q at maximal rates of work VO2 at same absolute rates of work are same as a man’s. Relative lactate threshold values are similar. . .

Key Points Adaptations to Acute Exercise For the same amount of muscle, there are no differences in strength between the sexes. Women have smaller muscle fibers and less muscle mass than men. Women have smaller left ventricles and lower blood volume, which reduce stroke volume. (continued)

Key Points (continued) Adaptations to Acute Exercise Women have similar cardiac outputs as men for the same rate of work, but that is achieved through higher heart rates, which account for lower stroke volumes. Women’s differences in respiratory response during exercise are mostly due to their smaller body size. VO2max values for women are generally lower than men’s due to women’s extra essential body fat, lower blood hemoglobin levels, and lower cardiac output. .

. Range of VO2max for Female Nonathletes, Male Nonathletes, Elite Female Athletes, and Elite Male Athletes Data from L. Hermansen and K.L. Andersen, 1965, "Aerobic work capacity in young Norwegian men and women," Journal of Applied Physiology 20: 425-431.

. VO2max Values for Elite Female and Male Distance Runners Compared With Average Values in Untrained Women and Men Data from S. Robinson, 1938, "Experimental studies of physical fitness in relation to age," Arbeitsphysiologie 10: 251-323; I. Astrand, 1960, "Aerobic work capacity in men and women with special reference to age," Acta Physiologica Scandinavica 49 (Suppl. 169); D.L. Costill and E. Winrow, 1971, "Maximal oxygen intake among marathon runners," Archives of Physical Medicine and Rehabilitation 51: 317-320; M.L. Pollock, 1977, "Submaximal and maximal working capacity of elite distance runners: Part I. Cardiorespiratory aspects," Annals of the New York Academy of Sciences 301: 310-322; RR. Pate et al., 1987, "Cardiorespiratory and metabolic responses to submaximal and maximal exercise in elite women distance runners," International Journal of Sports Medicine 8 (Suppl. 2): 91-95; and J.H. Wilmore and C.H. Brown, 1974, "Physiological profiles of women distance runners," Medicine and Science in Sports 6: 178-181.

Training and Body Composition in Women Decreases in fat mass and increases in fat-free mass (FFM), though women generally gain less FFM than men. Losses in body mass are more related to energy expenditure than participant’s sex. Density of weight-bearing bones increases equally in both sexes. Endurance training strengthens connective tissue in both sexes.

Neuromuscular Adaptations in Women Women’s magnitude of strength gained from resistance training is similar to men’s. Women generally don’t gain as much muscle size as men do from resistance training. Less muscle mass is a result of lower testosterone levels.

Men’s and Women’s World Weightlifting Records as of 2006 for the Total Amount of Weight Lifted

Key Points Adaptations to Exercise Training Women generally gain less FFM than men. Women can gain considerable strength but not large increases in muscle bulk. Cardiovascular and respiratory changes do not appear to be sex specific. Women experience the same relative increases in VO2max as men. (continued) .

Key Points (continued) Women’s Athletic Performance Men have more of an advantage than women in sports using upper body strength. The gap between men’s and women’s world records is narrowing. Since the 1970s more women are participating in sports and are being trained as hard as their male counterparts.

Phases of the Menstrual Cycle

Did You Know . . . ? Some female athletes have reportedly set world records during the flow phase while other women report that their performance is inhibited during this phase of the menstrual cycle. No general pattern has been found concerning the ability of women to achieve their best athletic performances during any specific phase of the menstrual cycle.

Cause or Effect? Menarche (the first menses) tends to come about 2 yrs later in higher-trained athletes in sports such as gymnastics and ballet than in other girls. Does intense training to achieve the level of elite athlete delay menarche, or does a later menarche provide an advantage that contributes to the success of an elite athlete?

Types of Menstrual Dysfunction Eumenorrhea is normal menstrual function. Oligomenorrhea is abnormally infrequent or scant menstruation. Amenorrhea is absence of menstruation. Primary amenorrhea is absence of first menses in women 18 and older. Secondary amenorrhea is absence of menstruation sometime after first menses.

Menstrual Dysfunction May occur in 2% to 12% of general population. May occur in 5% to 40% of female athletes. Risk increases with increased duration or intensity of training. Athletes can become pregnant while amenorrheic.

Possible Causes of Menstrual Dysfunction History of menstrual dysfunction Acute stress High training volume or intensity Low body weight or body fat Inadequate nutrition (energy deficit) and disordered eating Hormonal alterations

Concerns of Exercising During Pregnancy Reduced uterine blood flow leading to insufficient oxygen to the fetus The fetus could suffer from hyperthermia due to increased exercising temperature Reduced carbohydrate availability to the fetus The possibility of miscarriage and other dangers to the final outcome of pregnancy

Did You Know . . . ? The benefits of a properly prescribed exercise program during pregnancy outweigh the potential risks. It is important that the exercise program during pregnancy be coordinated with the woman’s obstetrician.

Cardiovascular Responses in Women Bone mineral loss with aging (especially in women) Estrogen deficiency Inadequate calcium intake before early 30s Inadequate physical activity Amenorrhea Anorexia nervosa

Did You Know . . . ? Disordered eating is not the same thing as eating disorders, yet both are causes for concern. The prevalence of both is higher among female athletes than male, especially in appearance, endurance, or weight-classification sports.

(a) Healthy Bone, and (b) Bone Showing Increased Porosity Resulting From Osteoporosis Reproduced from Journal of Bone and Mineral Research 1986, 1:15-21 with permission of the American Society for Bone and Mineral Research. Photos provided courtesy of D.W. Dempster.

Bone Mineral Content of Female Runners and Untrained Women Who Are Amenorrheic (Am) and Eumenorrheic (Eu) Unpublished data from Dr. Barbara Drinkwater.

Anorexia Nervosa Refusal to maintain more than the minimal normal weight based on age and height (<1%) Distorted body image Intense fear of fatness or gaining weight Amenorrhea

Bulimia Nervosa Recurrent episodes of binge eating (1-4%) A feeling of lack of control during binges Purging behavior—self-induced vomiting, laxative use, and/or diuretic use

Anorexia Athletica Not yet clinically recognized as eating disorder Intense fear of gaining weight or fat though underweight A weight loss of at least 5% accomplished by energy deficit Use of bingeing, self-induced vomiting, laxatives, or diuretics

Female Athlete Triad Disordered eating Secondary amenorrhea Bone mineral disorders

Key Points Environment and Performance Women have lower sweat rates due to lower sweat production, but this does not appear to inhibit their ability to tolerate heat. Women have more insulating subcutaneous fat than men and thus a slight advantage over men during cold exposure. Women’s smaller muscle mass limits their ability to generate as much body heat as men through shivering. Women and men have a similar response during exercise at altitude.