Sex Differences in Sport and Exercise: Physiology & Performance

1. Chapter 19 • Sex Differences in Sport and Exercise

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

3. 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

4. Table 19.1

5. 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

6. Figure 19.1

7. 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

8. 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

9. Figure 19.2

10. 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

11. Figure 19.3

12. 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

13. Figure 19.4

14. 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

15. Figure 19.5

16. 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

17. Figure 19.6

18. Figure 19.7

19. 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

20. 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

21. 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

22. 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?

23. Figure 19.8

24. 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

25. 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

26. 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

27. Figure 19.9a

28. Figure 19.9b

29. Figure 19.9c

30. Figure 19.9d

31. Figure 19.9e

32. Figure 19.9f

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

34. 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

35. Figure 19.10

36. 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

37. 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

38. Special Issues:Menstrual Dysfunction • 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

39. 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

40. 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

41. 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

42. 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.

43. 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

44. Table 19.2

45. 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

46. Figure 19.12

47. 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

48. 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)

49. 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

50. 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