WOMEN ARE NOT SMALL MEN: SEX DIFFERENCES AND PERFORMANCE. Stacy T Sims, PhD

Transcription

1 WOMEN ARE NOT SMALL MEN: SEX DIFFERENCES AND PERFORMANCE Stacy T Sims, PhD

2 OUTLINE Overview The Science: design and general assumptions The Menstrual Cycle: Fluid Balance Thermoregulation Metabolism: Fuel utilization, Acute recovery The Older Athlete: Peri/Post Menopause

3 OVERVIEW The large majority of exercise physiology research has been performed exclusively on male populations. Until the 80s, it was widely assumed the physiological responses of men were the same in women; Thus training, nutrition, and recovery strategies have been generalized to women without thought to viability of this generalization.

4 OVERVIEW Women are NOT small men.. Physiology is different- compounded by menstrual cycle hormones, and alterations in energy metabolism during exercise.

5 ASSESSING THE SCIENCE First- ask, IS there a sex difference, BEFORE trying to explain WHY there is one. Methods- menstrual cycle phase, age matched, fitness matched, sport matched, power (e.g. the number of participants)

6 THE SCIENCE: DESIGN AND GENERAL ASSUMPTIONS Often women are included, but in the follicular phase Or grouped together with men due to small n As of 2011, only ~10 studies in total have considered menstrual cycle variations in endurance exercise performance General assumptions: Differences are small, thus generalization is ok difficult to study women with two phases May result in a null finding

7 THE SCIENCE: DESIGN AND GENERAL ASSUMPTIONS General assumptions: curvilinear dosage response to carbohydrate 90g CHO per hour 4:1 ratio recovery Recovery time: acute, chronic; impact on adaptations

8 MAIN FACTORS Female physiology: Sex hormones: body water regulation, exercise capacity, triad - anaemia, thyroid, temperature *Progesterone is thermogenic, competes with aldosterone *Estrogen increases fluid retention- action on the kidneys; alters carbohydrate metabolism *Heat production during exercise/peak power and heat tolerance

9 Serum levels (ug) ENDOGENOUS MENSTRUAL CYCLE oestrogen Oestrogen progesterone Progesterone Time (Days) Follicular Phase Luteal Phase

10 Serum Concentrations (ug) TRIPHASIC OCPS VS. ENDOGENOUS HORMONES ethinyl-e progestin oestrogen progesterone Time (days)

11 Serum Concentrations (ug) TRIPHASIC OCPS AND ENDOGENOUS HORMONES Fluid 105 Handling 90 Thermoregulation Altered Metabolism 45 Recovery ethinyl-e progestin oestrogen progesterone Time (days)

12 FLUID BALANCE

13 ESTROGEN AND PROGESTERONE: INTERACTIONS Estrogen Osmoregulation: AVP, Posm AQP2 Plasma Volume N.O./Vasodilation Progesterone Volume Regulation: RAAS Receptor site competition with Aldosterone Inhibition of ANP Both modify each others actions, and are rarely found in isolation

14 ESTROGEN AND PROGESTERONE: FUNCTION Estrogen stimulates enos (renal and endothelial) preserves RBF via decreased endothelin expression attenuates RA-system mediated increases in oxidative stress (superoxide anion) Acts as a vasodilator to decrease vascular resistance acts centrally to lower the operating set-point of plasma osmolality (a leftward shift in AVP sensitivity) Progesterone (natural, non synthetic!) Receptor site competition with Aldosterone- induces transient natriuresis. Induces endotheliumdependent vascular relaxation Inhibition of ANP- this inhibition counteracts estrogen-mediated enos effects on TGF, allowing for decreased tubular perfusion

15 HORMONE MILIEU: RENAL HORMONES AND SEX HORMONES? Osmoregulation (osmolality, AVP) Volume Regulation (RAAS, ANP) Sensed? Plasma osmolality Effective tissue perfusion Sensors Hypothalamic Afferent arteriole; Atria; Osmoreceptors Carotid sinus baroreceptors) Effectors Arginine Vasopressin (AVP) Renin-angiotensin-aldosterone Thirst Atrial natriuretic peptide (ANP) Nor-Epinephrine Affected? Urine osmolality Urinary sodium Water intake Thirst

16 SOLUTES IN THE BLOOD- OSMOLALITY Plasma Osmolality normal values Men:~290 mosmol kg H 2 O -1 Women: 284 to 290 mosmol kg H 2 O -1 moderate hyponatremia is mosmol kgh 2 O -1 Menstrual cycle as a factor? (AVP, Aldosterone)

17 MEN S PV EXPANSION VS. WOMEN S PV EXPANSION 8 6 Change in plasma volume (%) High Sodium Low Sodium % Change in Plasma Volume Low Sodium-LowNa + High Sodium-HighNa Time (minutes, relative to exercise onset) pD 10 EX 98.8 min Time of Sampling Men: ~4% expansion, Women: high hormone phase, same % expansion (~4%)

18 PV EXPANSION BETWEEN PHASES 7 * * * Change in plasma volume (%) Drinking > OCPhigh OCPlow NAThigh NATlow Time (min with respect to start of drinking) PV expansion: low hormone %, high hormone 3.5-4%

19 HYPONATREMIA Women- more reports of hyponatremiacould be phase dependent In exercise, most often attributed to smaller body size and longer endurance times; menstrual phase not reported Key point: Estrogen acts centrally to decrease osmotic set point of AVP release: basal plasma osmolality is higher in the follicular than in the luteal phase, with the threshold for AVP release lowest in the luteal phase Fol.phase: ~290 mosm kg H 2 O -1 Lut.phase: ~280 mosm kg H 2 O -1 Confounders: hypothyroidism, NSAIDS

20 KEY POINTS: HIGH HORMONE RESETS BODY TO LOWER PLASMA VOLUME, AND BASELINE SENSITIVITY TO OSMOLALITY CHANGES FASTER RATE TO FATIGUE; HYPONATREMIA MORE COMMON IN WOMEN

21 THERMOREGULATION

22 ARE THERE DIFFERENCES? Changing rate of sex hormone release during the menstrual cycle modifies thermoregulation in women! -perturbations in resting body temperature -perturbations in thresholds for thermal responses to heat loads (positive and negative loads)

23 THERMOREGULATION: (IMPACT ON EXERCISE TOLERANCE) Thermoregulation Sweat rate Slightly better sweating efficiency? Slight impediment to heat loss due to skin-fold thickness Estrogen and Progesterone influences on plasma volume and respiration Adaptive responses to heat Similar Luteal phase: T core 0.3 C at rest More during submax exercise? Rating of Perceived Exertion (RPE) Anaerobic metabolism?

24 POST EXERCISE COOLING FOR RECOVERY (As compared to men..) Women have a reduced ability to offload heat postexercise (Kenny&Jay, JAP 2009) Due to greater skin blood flow with greater drop in arterial blood pressure; Plus Progesterone s thermogenic effect on core temperature with reset of threshold to sweat

25 POST EXERCISE COOLING FOR RECOVERY Cool water immersion and cool water perfused vests enhance recovery by reducing internal thermal load via: Redistribution of blood flow Decreased CNS command on muscle activity Metabolic waste removal

26 KEY POINT: THE LUTEAL PHASE OF THE MENSTRUAL CYCLE AFFECTS THERMOREGULATION MORE SO THAN FOLLICULAR. OCP COMPOUNDS THIS EFFECT. LESS HEAT TOLERANCE IN HIGH HORMONE PHASE.

27 METABOLISM: CARBOHYDRATE VS PROTEIN VS FAT?

28 ESTROGEN- EFFECTS DURING EXERCISE Decreases reliance on liver glycogen Increases fatty acid utilization Decreases amino acid breakdown Why?- due to reduced catecholamine release at a given intensity-workload as compared to similarly trained menthus need a second means of fueling the muscle. Greater effect during high hormone phase (harder to hit intensities due to glycogen sparing effect)

29 ESTROGEN- EFFECTS DURING EXERCISE Studies performed by carbohydrate depleted women without supplementation were able to maintain blood glucose during the follicular phase, but not the luteal phase.(zderic et al. JAP 2008; Tarnopolsky MSSE 2008)

30 TRANSLATED TO PRACTICAL Women have a greater capacity for burning fat at a given intensity, sparing glycogen Curvilinear dosage data does not identify women, nor take into account estrogen perturbations (Intentionally left blank) (Intentionally left blank) (Intentionally left blank) (Intentionally left blank)

31 PROGESTERONE- EFFECTS DURING EXERCISE (Thermogenic) Competes with aldosterone, thus increased sodium excretion Increases protein catabolism Can have anti-estrogenic effects

32 TRANSLATED TO PRACTICAL Women have a greater capacity for burning fat at a given intensity, sparing glycogen AND reduced muscle adaptation due to increased protein catabolism To facilitate recovery and adaptations (intentionally left blank).

33 RECOVERY

34 RECOVERY PHASES DIFFER Although women mobilize more fat during exercise, the inverse is true during recovery Bottom line: What the????????? Women use more fat during exercise, have greater fat stores, and show a better propensity to store glycogen while maintaining a steady energy flow during exercise; but have a shorter window for recovery (3 hours post exercise women are close to baseline metabolic rates; whereas men are still elevated up to 21 hours post) Contributes to increased difficulty to lean up

35 RECOVERY STRATEGIES (Slide intentionally left blank)

36 THE OLDER ATHLETE: PERI AND POST MENOPAUSE

37 TAKE THE HORMONE FLUX AWAY Less vessel compliance Less power production- neuromuscular and muscle quality Smaller window of core temperature flux tolerance Sweat thresholds reset Sodium effects- renal hormones Carbohydrate sensitivity; increased need for protein; less fat

38 SUMMARY Women are not small men. Physiology differences alter thermoregulatory responses; metabolism during and post exercise Training programs (including recovery!!) should take menstrual cycle perturbations into account to limit overtraining and decreased training adaptations.

39 QUESTIONS?