sex differences in sport and exercise

18

Sex Differences in Sport and Exercise

chapter

Learning Objectives

• Learn about differences in body composition between men and women and the roles of sex hormones in development

• Examine how fat is stored• Find out the differences in upper and lower body

strength between men and women• Learn about sex differences in the cardiovascular and

respiratory responses to acute exercise• Examine the cardiovascular and metabolic adaptations

to endurance and resistance training in men and women

(continued)

Learning Objectives (continued)

• Learn about the normal menstrual cycle and how excessive physical activity or energy deficit can impair it

• Examine the risks and benefits of exercising during pregnancy

• Learn about sex differences in the risk for osteoporosis• Examine the relationship between eating disorders,

bone mineral loss, and amenorrhea, known as the female athlete triad

• Discover whether women and men differ in their exercise response to altitude, heat, humidity, and cold

Introduction: Sex Differencesin Athletic Performance

Things to consider:• True biological differences • Social differences • Historical cultural restrictions

Body Size and Composition

• Puberty in girls: follicle stimulating hormone (FSH) and luteinizing hormone (LH) cause estrogen production from the ovaries– Causes pelvis broadening– Breast development– Fat deposition in hips and thighs– Increased bone growth

• Puberty in boys: FSH and LH cause testosterone production from the testes – Increased bone formation and muscle mass– Stimulates EPO production from the kidneys

Changes in Blood Concentrationsof 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

1. Estrogen increases activity of lipoprotein lipase, which is produced by fat cells

2. Lipoprotein lipase is bound to walls of capillaries

3. Chylomicrons—major transporter of triglycerides—pass by in the blood

4. Lipoprotein lipase traps the chylomicrons, hydrolyzes the triglycerides, and transports them to fat cells

5. A decrease in lipolytic activity at the sites of fat storage makes it difficult to lose fat

Body Size and Composition

Key Points• Until puberty, girls and boys do not differ significantly in

most measurements of body size and composition• At puberty, because of the influence of sex hormones,

body composition begins to change• Testosterone increases bone formation and protein

synthesis, leading to a larger FFM • Estrogen causes the increase in fat deposition in

females, particularly in the hips and thighs, and an increased rate of bone growth

Physiological Responsesto Acute Exercise: Strength

• Innate qualities of muscle and motor control are similar for men and women

• Women and men do not differ in lower body strength expressed relative to body weight or to FFM

• Women have less upper body strength expressed relative to body weight or FFM than men

• Women’s muscle mass is largely below the waist, and they use their lower body muscles more than their upper body muscles

• Muscle fiber cross-sectional area is smaller and muscle mass is less in women

No Sex Differences Are Observed in Indexesof Strength 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 Fibersin the Vastus Lateralis Musclein 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.

Responses to Acute Exercise

Key Points• Muscle qualities and mechanisms of motor control are

similar between men and women• Women do not differ from men in lower body strength

when expressed relative to body weight• Women have less upper body strength than men

expressed relative to body weight or FFM

Cardiovascular Responsesin Women

• Higher heart rate (HR) response for any submaximal power output

• Similar HRmax

• Similar cardiac outputs (Q) at any absolute submaximal power output

• Lower stroke volume due to smaller heart size and blood volume

• Lower hemoglobin content

• Compensatory increase in (a-v)O2 diff

• Less potential for increasing (a-v)O2 diff

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Comparison of Submaximal Heart Rate (HR), Stroke Volume (SV), and Cardiac Output (Q) Between Men and Women

Data from HERITAGE Family Study, 2001.

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Respiratory Responses in Women

• Differences in responses are mostly due to differences in body size

• Breathing frequency is similar at the same relative power output but is increased at the same absolute 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

• VO2max differences between men and women must be carefully interpreted

• Average VO2max after puberty is 70-75% of that of an average man More sex-specific essential body fat Lower hemoglobin concentrations Lower Q at maximal rates of work

• Lactate threshold values are similar between the sexes

• Decreased peak lactate concentrations in women

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Range of VO2max for Female and Male Nonathletes and for Female and

Male Elite 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.

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VO2max Values for Elite Female and Male Distance Runners Compared With Average

Values in Untrained Women and Men

Data from S. Robinson, 1938; I. Åstrand, 1960; D.L. Costill and E. Winrow, 1970; M.L. Pollock, 1977; R.R. Pate et al., 1987; and J.H. Wilmore and C.H. Brown, 1974.

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Responses to Acute Exercise

Key Points• At submaximal exercise intensities women have

higher HR than men, but women’s Q are similar for the same rate of work

• Women have lower SV, primarily because they have smaller hearts and less blood volume

• Sex differences in respiratory responses are primarily due to body size differences

• VO2max values for women are generally lower than men’s due to women’s greater fat mass, lower hemoglobin concentration, and lower Qmax

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Training and Body Composition in Women

• With either cardiorespiratory endurance training or resistance training, both men and women:• ↓ Total body mass • ↓ Fat mass• ↓ Relative fat mass• ↑ FFM

• Magnitude of changes in body composition are more related to energy expenditure than participant’s sex

• Density of long bones increases with weight-bearing exercise

• Connective tissue is strengthened with endurance training

Strength Training

• Women have less muscle mass• Similar to men, women gain considerable strength

through strength training• Strength gains are usually not accompanied by a large

increase in muscle bulk• Similar increases in FFM, through hypertrophy of type I,

type IIa, and type IIx muscle fibers

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

of Weight Lifted by Weight Category

International Weightlifting Federation, August 2006 (www.iwf.net/events/wr/record_cur.php).

Cardiovascular Adaptationsto Exercise Training

• SV increases as a result of increased blood volume and increased contractility

• HR is reduced at any given submaximal power output

• Increase in VO2max results from increases in Qmax and small increases in (a-v)O2 difference

• Maximal ventilation is increased• Cardiovascular and respiratory changes that

accompany endurance training do not appear to be sex specific

..

Metabolic Adaptationsto Exercise Training

• Women experience the same average relative increase in VO2max compared to men (~15-20%)

• Magnitude depends on intensity and duration of the training sessions

• Blood lactate concentrations are reduced for the same submaximal work rate

• Peak lactate concentrations are increased

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Sport Performance

Sex differences are more pronounced in events where high levels of upper body strength are required (e.g., shot put)

Women’s and Men’s World Records in Six Running Events Between 1960 and 2006

(continued)

Women’s and Men’s World Records in Six Running Events Between 1960 and 2006

(continued)

Special Issues

• Menstruation and menstrual dysfunction• Pregnancy• Osteoporosis• Eating disorders• Environmental factors

Phases of the Menstrual Cycle

Menstruation and Performance

• There appears to be no general pattern concerning the ability of women to achieve their best performances during any specific phase of their menstrual cycle

• Women with premenstrual syndrome or dysmenorrhea will likely not perform as well while experiencing symptoms

Menarche

• Menarche: the first menstrual period • Tends to come later in highly trained athletes in sports

such as gymnastics and ballet compared to average girls

• Median age of menarche for American girls is 12.4-13.0 vs. 14.5 for gymnasts

• Successful athletes in these performance sports tend to have small, lean bodies

Types of Menstrual Dysfunction

Eumenorrhea: normal menstrual function

Oligomenorrhea: abnormally infrequent or scant menstruation or menses occurring at intervals greater than 35 days

Amenorrhea: absence of menstruation– Primary amenorrhea: the absence of first menses in women 16 and older (e.g., women who never begin menstruating)– Secondary amenorrhea: the absence of menstruation sometime after first menses

Menstrual Dysfunction

• May occur in 5% to 60% or higher of female athletes depending on the sport or activity and the level of competition

• Risk increases with increased duration or intensity of training

• Athletes can become pregnant while amenorrheic

Possible Causesof Menstrual Dysfunction

• History of menstrual dysfunction• Acute stress• High training volume or intensity• Low body weight or body fat• Hormonal alterations• Energy deficit through inadequate nutrition and/or

disordered eating

Athletes and the Menstrual Cycle

Key Points• The effects of different phases of the menstrual cycle

on performance are subject to considerable variation• Menarche can occur late in some young athletes in

certain sports because of late maturity or lean body build

• Female athletes can experience menstrual dysfunction, most often secondary amenorrhea or oligomenorrhea

• Inadequate nutrition, or a prolonged energy deficit, is most likely the cause of secondary amenorrhea

• Hormonal changes from exercise training might disrupt the GnRH secretion needed to direct the menstrual cycle

Concerns of Exercising During Pregnancy

1. Reduced uterine blood flow leading to fetal hypoxia

2. Fetal hyperthermia associated with the increase in the mother’s internal body temperature (e.g., prolonged exercise in the heat)

3. Reduced carbohydrate availability to the fetus

4. The possibility of miscarriage and other dangers to the final outcome of pregnancy

Exercise Guidelines During Pregnancy

• Pregnant women can derive benefits from mild to moderate exercise (at least 3 days/week)

• Women should avoid supine exercise and motionless standing after the first trimester

• Women should stop exercising when fatigued and should not exercise to exhaustion

• Care should be taken not to participate in sports or exercise in which falling, a loss of balance, or blunt abdominal trauma may occur

(continued)

Exercise Guidelines During Pregnancy (continued)

• Exercising women should pay particular attention to diet to ensure that they are receiving adequate calories

• Heat dissipation is of particular concern, so pregnant women should wear the correct clothing, ensure sufficient fluid intake, and select optimal environmental conditions

• A woman’s regular prepregnancy exercise routine should be resumed gradually postpartum

Benefits of Exercise During Pregnancy

• The benefits of a properly prescribed exercise program during pregnancy outweigh the potential risks

• Exercise programs during pregnancy should be coordinated with the woman’s obstetrician

Osteoporosis

• Osteoporosis: decreased bone mineral content which causes increased bone porosity

• Osteopenia: loss of bone mass that occurs with aging• Bone mineral loss for women starts in the 30s• Three major contributing factors common to

premenopausal women:– Estrogen deficiency– Inadequate calcium intake– Inadequate physical activity

(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.

a b

Osteoporosis and Amenorrheic Athletes

• Athletes with secondary amenorrhea are at increased risk for bone mineral losses

• This loss does not appear to be totally reversible with the resumption of normal menstrual function

Bone Mineral Content of Female Runners and Untrained Women Who Are

Amenorrheic (Am) and Eumenorrheic (Eu)

Unpublished data from Dr. Barbara Drinkwater.

Eating Disorders

• Eating disorders: a group of disorders that must meet specific criteria established by the American Psychiatric Association– Anorexia nervosa– Bulimia nervosa

• Disordered eating: patterns of eating that are not considered normal but don’t meet the specific diagnostic criteria for a given eating disorder

Anorexia Nervosa

• Refusal to maintain more than the minimal normal weight based on age and height

• Distorted body image• Intense fear of fatness or gaining weight• Amenorrhea

Bulimia Nervosa

• Recurrent episodes of binge eating• A feeling of lack of control during binges• Purging behavior, which can include self-induced

vomiting, laxative use, and/or diuretic use

3 Categories of High-Risk Sportsfor Disordered Eating

1. Appearance sports: diving, figure skating, gymnastics, bodybuilding, and ballet

2. Endurance sports: distance running and swimming

3. Weight-classification sports: horse racing (jockeys), boxing, and wrestling

Female Athlete Triad

• Disordered eating• Secondary amenorrhea• Bone mineral disorders

Environmental Factors

• Women and men respond almost identically to heat stress when exercise intensity is adjusted to an individual’s VO2max

• 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 body heat

• Women and men have a similar response during maximal exercise at altitude, but differences might exist at rest and during submaximal exercise

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