Sex Differences in Sport and Exercise Chapter 19 Sex Differences in Sport and Exercise

Chapter 19 Overview Body size and composition Physiological responses to acute exercise Physiological adaptations to exercise training Sport performance Special issues

Introduction to Sex Differences in Sport and Exercise For decades, culture, athletic governing bodies, and PE curricula perpetuated the myth that girls and women should not compete in sport Last 30 to 40 years, girls and women have achieved great athletic feats Sex differences in performance still exist Separating biological versus other factors

Table 19.1

Body Size and Composition Testosterone leads to –  Bone formation, larger bones –  Protein synthesis, larger muscles –  EPO secretion,  red blood cell production Estrogen leads to –  Fat deposition (lipoprotein lipase) Faster, more brief bone growth Shorter stature, lower total body mass –  Fat mass, percent body fat

Figure 19.1

Body Size and Composition Distinct female fat deposition pattern Rapid storage on hips and thighs due to  lipoprotein lipase activity •  Lipolytic activity makes regional fat loss more difficult Lipoprotein lipase , lipolysis  during third trimester of pregnancy, lactation

Physiological Responses to Acute Exercise Muscle strength differs between sexes Upper body: women 40 to 60% weaker Lower body: women 25 to 30% weaker Due to total muscle mass difference, not difference in innate muscle mechanisms No sex strength disparity when expressed per unit of muscle cross-sectional area

Figure 19.2

Physiological Responses to Acute Exercise Causes of upper-body strength disparity Women have more muscle mass in lower body Women utilize lower body strength more Altered neuromuscular mechanisms? Women: smaller cross-sectional areas Similar fiber-type distribution Research indicates women more fatigue resistant

Figure 19.3

Physiological Responses to Acute Exercise Cardiovascular function differs greatly For same absolute submaximal workload Same cardiac output Women: lower stroke volume, higher HR (compensatory) Smaller hearts, lower blood volume For same relative submaximal workload Women: HR slightly , SV , cardiac output  Leads to  O2 consumption

Figure 19.4

Physiological Responses to Acute Exercise Women compensate for  hemoglobin via  (a-v)O2 difference (at submaximal intensity) (a-v)O2 difference ultimately limited, too Lower hemoglobin, lower oxidative potential Sex differences in respiratory function Due to difference in lung volume, body size Similar breathing frequency at same relative workload Women  frequency at same absolute workload

Figure 19.5

Physiological Responses to Acute Exercise Women’s VO2max < men’s VO2max Untrained sex comparison unfair Relatively sedentary nonathlete women Relatively active nonathlete men Trained sex comparison better Similar level of condition between sexes May reveal more true sex-specific differences

Figure 19.6

Figure 19.7

Physiological Responses to Acute Exercise Can scale VO2max to other body variables Height, weight, FFM, limb volume Sex difference minimized or gone with scaling Simulated women’s fat mass on men Reduced sex differences in treadmill time, submaximal VO2 (ml/kg), VO2max Women’s additional body fat major determinant of sex-specific difference in metabolic responses

Physiological Responses to Acute Exercise Women’s lower hemoglobin limits VO2max Women’s lower cardiac output limits VO2max SVmax limited by heart size, plasma volume Plasma volume loading in women helps Submaximal absolute VO2: no sex difference in SV Sex differences in lactate, threshold Peak lactate concentrations lower in women Lactate threshold occurs at same percent VO2max

Physiological Adaptations to Exercise Training Body composition changes Same in men and women –  Total body mass, fat mass, percent body fat –  FFM (more with strength vs. endurance training) Weight-bearing exercise maintains bone mineral density Connective tissue injury not related to sex

Physiological Adaptations to Exercise Training Strength gains in women versus men Less hypertrophy in women versus men, though some studies show similar gains with training Neural mechanisms more important for women Variations in weight lifted for equivalent body weight For given body weight, trained men have more FFM than trained women Fewer trained women Factors other than FFM?

Figure 19.8

Physiological Adaptations to Exercise Training Cardiorespiratory changes not sex specific Aerobic, maximal intensity –  Qmax due to  SVmax ( preload, contractility) –  Muscle blood flow, capillary density –  Maximal ventilation Aerobic, submaximal intensity Q unchanged –  SV,  HR

Physiological Adaptations to Exercise Training VO2max changes not sex specific ~15 to 20% increase –  Qmax,  muscle blood flow Depends on training intensity, duration, frequency Lactate threshold  Blood lactate for given work rate  Women respond to training like men do

Sport Performance Men outperform women by all objective standards of competition Most noticeable in upper-body events Gap narrowing Women’s performance drastically improved over last 30 to 40 years Leveling off now Due to harder training

Figure 19.9a

Figure 19.9b

Figure 19.9c

Figure 19.9d

Figure 19.9e

Figure 19.9f

Special Issues Menstruation, menstrual dysfunction Pregnancy Osteoporosis Eating disorders Environmental factors

Special Issues: Menstruation Normal menstrual function Menstrual (flow) phase Proliferative phase (estrogen) Ovulation—follicle stimulating hormone (FSH), luteinizing hormone (LH) Secretory phase (estrogen, progesterone) Cycle length ~28 days, can vary

Figure 19.10

Special Issues: Menstruation No reliable data indicate altered athletic performance across menstrual phases No physiological differences in exercise responses across menstrual phases World records set by women during every menstrual phase

Special Issues: Menstrual Dysfunction Menarche: first menstrual period May be delayed in certain sports (e.g., gymnastics) Delayed menarche: after age 14 Delayed-menarche athletes self-select? Sport may not  delayed menarche Small, lean athletic girls (delayed menarche candidates) may gravitate to sport

Special Issues: Menstrual Dysfunction Seen more in lean-physique sports Eumenorrhea: normal Oligomenorrhea: irregular Amenorrhea (primary, secondary): absent Can affect 5 to 66% of athletes Menstrual dysfunction ≠ infertility

Special Issues: Menstrual Dysfunction Secondary amenorrhea—caused by energy deficit (inadequate caloric intake) –  LH pulse frequency –  T3 secretion –  Estrogen, progesterone May also involve GnRH, leptin, cortisol As long as caloric intake adequate, exercise does not  secondary amenorrhea

Special Issues: Pregnancy Concerns 1. Acute reduction in uterine blood flow (shunt to active muscle)  fetal hypoxia 2. Fetal hyperthermia from increase in maternal core temperature 3. Maternal CHO usage , thereby  CHO availability to fetus 4. Miscarriage, final outcome of pregnancy

Special Issues: Pregnancy Research •  Uterine blood flow may not  hypoxia Uterine (a-v)O2 difference  may compensate Fetal HR  due to maternal catecholamines Fetal hyperthermia: unresolved CHO availability: unresolved Miscarriage, final pregnancy outcome Data scarce, conflicting Many studies show favorable (or no) effects

Special Issues: Pregnancy Recommendations Mild-to-moderate exercise 3 times/week No supine exercise after first trimester Stop when fatigued Non-weight-bearing exercise preferable No risk of falling, loss of balance, etc.

Special Issues: Pregnancy Recommendations Ensure adequate caloric intake Dress and hydrate to avoid heat stress Prepregnancy exercise routine should be gradually resumed postpartum No scuba diving Benefits > risks if cautiously undertaken

Table 19.2

Special Issues: Osteoporosis Osteopenia versus osteoporosis Risk greater in women especially after menopause Slowed and retarded by weight-bearing exercise Major contributing factors Estrogen deficiency Inadequate calcium intake Inadequate physical activity Amenorrhea, anorexia nervosa

Figure 19.11a

Figure 19.11b

Figure 19.12

Special Issues: Osteoporosis Estrogen supplementation Originally prescribed to reverse osteoporosis Higher risk of cancer, stroke, heart attack Bisphosphonates Antiresorptive medication May slow, stop bone degeneration Preventive Diet, lifestyle –  Ca2+, vitamin D intake Exercise, maintain eumenorrhea

Special Issues: Eating Disorders Anorexia nervosa Refusal to maintain minimal normal weight Distorted body image, fear of fatness Amenorrhea Bulimia nervosa Recurrent binge eating Lack of control during binges Purging behaviors (vomiting, laxatives, diuretics)

Special Issues: Eating Disorders Young women at highest risk Eating disorder versus disordered eating Worse in certain sports Appearance sports: diving, figure skating, ballet Endurance sports: distance running, swimming Weight-class sports: jockeys, boxing, wrestling Perfectionists, competitive, under tight control Self-reporting underestimates prevalence

Special Issues: Eating Disorders Eating disorders considered addictions Behavior reinforced by media, parents, coaches Very difficult to treat Often accompanied by denial Life threatening, expensive to treat Must seek out trained clinical specialist

Table 19.3

Special Issues: Female Athlete Triad Syndrome of interrelated conditions Energy deficit  secondary amenorrhea  low bone mass Disordered eating may (not) be involved Three disorders can occur alone or in combination, must be addressed early Treatment:  caloric intake,  activity (in some cases)

Special Issues: Environmental Factors Heat stress issues Women:  sweat production No sex differences in thermal tolerance Cold stress issues Women: better insulated ( subcutaneous fat) Men: better shivering thermogenesis ( FFM) Altitude stress issues VO2max decreases No sex differences in altitude tolerance