Phys TBL 2

the large majority of exercise physiology research has been performed exclusively in which populations?

18-22 year old college aged men

• until the 1980s it was assumed that men and women would have the same physiological responses to exercise and nutrition

nutrition/exercise/recovery strategies have been generalized to women when they should not be

most studies dont involve women and if they do they are poorly designed

• if women are included they are usually in follicular phase (hormones low)

• small sample sizes so they group women + men together

• researchers believe it is too difficult to study women with two phases

follicular phase

low hormone phase

luteal phase

high hormone phase

day 1

• first day of bleeding

• first day of follicular phase

key difference between men and women

menstrual cycle

• women also sometimes take hormonal birth control

average woman’s cycle

28 day cycle dictated by cyclical changes in hormones regulated by the endocrine system

most abundant form of estrogen

estradiol (specifically 17β-estradiol)

estradiol at each point of cycle

• low at beginning of follicular phase

• gradual increase and peak at second half of follicular phase

• sharp drop off at end of luteal phase (lowest at ovulation)

• slight increase through first half of luteal phase

• slight decrease (back to baseline) at end of luteal phase

luteinizing hormone (LH) at each point of cycle

• very low at beginning of follicular phase, stays the same level

• half way through follicular phase, small and quick bump up then back to same level

• big, quick increase to peak at end of follicular phase right before ovulation

• at ovulation goes back down to original level and stays there through entire luteal phase

follicle stimulating hormone (FSH) at each point of cycle

• slight increase through first part of follicular phase

• goes down (at same time that LH peak goes back down) in middle follicular phase

• small peak right at ovulation (slightly before it)

• back down at consistent low level through luteal phase

• very slight increase at end of luteal

progesterone at each point of cycle

• stays at same level through all of follicular phase (low)

• after ovulation it goes up

• through entire luteal phase goes steadily up to peak and steadily back down to baseline

prolactin-releasing hormone (PRH) in the hypothalamus (pathway after)

ACTIVATES → prolactin (PRL) in the anterior pituitary → breast (milk production in mammary glands)

prolactin inhibiting hormone (PIH/dopamine) in the hypothalamus (pathway after)

INHIBITS → prolactin (PRL) in anterior pituitary → milk production is inhibited

thyrotropin-releasing hormone (TRH) in the hypothalamus (pathway after)

ACTIVATES → prolactin (PRL) in anterior pituitary → breast (milk production stimulated)

OR

ACTIVATES → thyroid stimulating hormone (TSH) in the anterior pituitary → ACTIVATES thyroid gland → thyroid hormones (T3, T4) → many tissues

corticotropin releasing hormone (CRH) in the hypothalamus (pathway after)

ACTIVATES adrenocorticotropic hormone (ACTH) in anterior pituitary→ ACTIVATES adrenal cortex → cortisol → many tissues

growth hormone releasing hormone (GHRH/somatocrinin) in the hypothalamus (pathway after)

ACTIVATES growth hormone (GH)(somatotropin) in anterior pituitary → many tissues

OR

ACTIVATES growth hormone (GH)(somatotropin) in anterior pituitary → ACTIVATES liver → somatomedins (IGF) → many tissues

growth hormone inhibiting hormone (GHIH somatostatin) in hypothalamus (pathway after)

INHIBITS growth hormone (GH)(somatotropin) in anterior pituitary → inhibits effects in tissues/liver

gonadotropin releasing hormone (GnRH) in hypothalamus pathway on FSH

GnRH ACTIVATES → follicle stimulating hormone (FSH) in anterior pituitary → germ cells of gonads

OR

GnRH ACTIVATES → FSH in anterior pituitary → ACTIVATES endocrine cells in gonads → androgens/estrogens/progesterone → germ cells of gonads

gonadotropin releasing hormone (GnRH) in hypothalamus pathway on LH

GnRH ACTIVATES luteinizing hormone (LH) in anterior pituitary → germ cells of gonads

OR

GnRH ACTIVATES luteinizing hormone (LH) in anterior pituitary → ACTIVATES endocrine cells in gonads → androgens/estrogen/progesterone → germ cells of gonads

progesterone competes with the same receptor site for:

• aldosterone (key for sodium balance) and

• anti-diuretic hormone (ADH (arginine vasopressin) key for water balance)

key for water and thirst

2 weeks preceding the start of the woman’s period

high estrogen and progesterone

• significant physiological changes

• peak felt ~5 days before bleeding

significant changes in 2 weeks preceding start of period

• drop in plasma volume by 8%

• increase in core temperature by ~0.5 °C

• change in metabolism to spare glycogen and increase reliance on fatty acids

• increased amount of muscle catabolism from progesterone

• increased amount of total body sodium losses

• reset of plasma osmolarity

drop in plasma volume by ~8% WHEN?

in 2 weeks preceding start of period

• PV is ~3L of the total ~5.5L of blood volume (intravascular compartment)

• remaining ~2.5L consists of cellular elements of blood

• less total blood for circulation and thermoregulation

increase in core temperature by ~0.5°C in 2 weeks preceding start of period does what

• shortening the time to fatigue

• decreasing heat tolerance

change in metabolism in 2 weeks preceding start of period

change to spare glycogen and increase reliance on fatty acids

• reduce woman’s ability to use glucose as fuel

• reduce woman’s ability to build lean muscle

increased muscle catabolism from progesterone in 2 weeks preceding start of period has what impact on exercise?

• reduces ability to recover well

• reduces ability to build lean muscle

increased amount of total body sodium losses in 2 weeks preceding start of period is from which hormone?

this is from progesterone

reset of plasma osmolarity in 2 weeks preceding start of period

• lower plasma osmolarity

• predisposes women to hyponatremia

estrogen and VO2 max in 2 weeks preceding start of period

• estrogen blunts VO2 max from a metabolic and respiratory aspect

• VO2 max is one of the best measures of aerobic fitness

• cant access carbohydrate

• increased respiratory rate

• hard to hit the top end of VO2

CNS fatigue in 2 weeks preceding start of period

• estrogen and progesterone affect CNS fatigue

• lack of “mojo”: cant do exercises as well as they usually can

increase in blood osmolarity leads to:

osmoreceptor cells in hypothalamus detect increase in blood osmolarity →

release of ADH in pituitary gland →

collecting duct: increased permeability →

H2O reabsorption helps prevent further osmolarity increase →

back to homeostasis

*at the same time, osmoreceptors promote thirst → drinking reduces blood osmolarity back to set point → back to homeostasis

what can cause low blood volume/blood pressure?

• dehydration

• loss of blood

low blood volume/blood pressure leads to:

juxtaglomerular apparatus (JGA) → renin production → angiotensinogen → angiotensin II

AFTER angiotensin II, could be 2 pathways:

angiotensin II → arteriole constriction → homeostasis

OR

angiotensin II → adrenal gland → aldosterone → increased Na+ and H2O reabsorption in distal tubules → homeostasis

birth control pills

• circulating amount of estrogen is 6-8x as high

• “low hormone/placebo week”" is not actually low hormone

• estrogen rebounds and results in high circulating amount of estrogen

IUD

• better than pills

• localized doses of progesterone

• significantly reduces amount of hormones circulating

peri- and post-menopausal women: additional challenge

• predisposition to store abdominal fat (leftover signals from estrogen)

• much more difficult time maintaining muscle integrity

why do peri- and post-menopausal women struggle to maintain muscle integrity

• increased catabolic drive: decreases muscle reparation and hypertrophy

• difficult time gaining and maintaining lean mass

• difficulty with neuromuscular drive to produce power

men dont have any of this (booo!)

during prolonged exercise, what happens to fluid and salt

• fluid and salt losses through sweating

• reduce plasma volume

• leads to heart rate drift, hyperthermia, and reduction in performance

oral rehydration with water

• reduces loss of plasma volume

• lessens heart rate drift

• lessens hyperthermia

inclusion of sodium in rehydration solution (~90mmol/l Na+)

• double the sodium volume in sweat

• restores plasma volume when ingested during exercise

• expands plasma volume if ingested pre-exercise

hydration during exercise in real person speak

• during exercise you lose water and salt through sweat

• when you lose this water and salt, the watery part of blood also drops

• less water in blood = blood more viscous

• higher heart rate, lower power production, greater rise in core temp

• leads to fatigue, reduced performance, and power decline at the end of a race

competition in the body during exercise

muscles and skin fight for blood

• blood goes to muscles for metabolic function

• blood goes to skin to get rid of heat produced by working muscles

• when body water drops, competition becomes more fierce

• skin blood flow wins: heat is a greater threat to body than keeping muscles working (which produces heat)

fatigue during exercise

• due to drop in blood flow to muscle

• less metabolism functioning

• protein denaturing (contractile proteins denature in >~39°C)

most researchers recommend what amount to prevent fluid loss in exercise?

all athletes drink 10-12 ml of fluid per kg of bodyweight per hour (750-900 ml for 75 kg person) during exercise

new research on exercise/fluid loss

if you are exercising and maintaining your core body temp (not cold) you can drink according to thirst without performance decrements

difference between men and women for hydration

• composition of the drink

• NOT fluid needs per hour

two most influential female sex hormones

estrogen and progesterone

• both change concentration across menstrual cycle and by oral contraceptive pill (OCP) usage

• both influence sodium and water distribution (and thus fluid compartment volumes and dynamics)

estrogen and fluid

estrogens favor fluid retention

• activating renin-angiotensin-aldosterone system

• enhances vasodilation and capillary permeability

• acts centrally to lower the operating set point of plasma osmolality (leftward shift in ADH sensitivity)

progesterone and fluid

antagonizes the renin-angiotensin-aldosterone system

• does this through antagonism of the aldosterone receptor

• competes directly with the same mineralcorticoid receptor as aldosterone

• this could cause a transient natriuresis

progesterone makes you pee

natriuresis

increase in excretion of sodium through urine

estrogen/progesterone fluid impacts

concentrations of sex hormones have dramatic impacts on fluid

liver secretes WHAT?

liver secretes angiotensinogen → which turns into angiotensin I

decrease in renal perfusion (juxtaglomerular apparatus) does WHAT?

stimulates kidney to secrete renin → which stimulates angiotensinogen to change to angiotensin I

angiotensin I does what next?

the kidney and lungs secrete ACE, which stimulates the reaction: angiotensin I → angiotensin II

angiotensin II stimulates WHAT?

• sympathetic activity

• tubular Na+Cl- reabsorption and K+ excretion (H2O retention)

• adrenal gland/cortex

• arteriolar vasoconstriction (increase in BP)

• pituitary gland posterior lobe

what is the effect of angiotensin II stimulating the adrenal gland/cortex?

secretes aldosterone → stimulates H2O retention

what is the effect of angiotensin II stimulating the posterior lobe of the pituitary gland?

secretes ADH, which stimulates → collecting duct (H2O absorption)

what is the overall impact of the renin-angiotensin-aldosterone system?

• water and salt retention

• effective circulating volume increases

• perfusion of the juxtaglomerular apparatus increases

plasma volume is highest WHEN?

the preovulatory phase of the menstrual cycle

• when estrogen levels are increasing

plasma volume at midluteal phase

• drops as much as ~8%

• due to fluid and protein movement into the interstitium

• this is caused by the effects of estrogen on plasma albumin and plasma colloid osmotic pressure

how does estrogen effect plasma in midluteal phase

• plasma proteins (such as albumin) are too large to penetrate the capillary wall freely

• presence of greater concentration of plasma proteins in the intravascular compartment (in comparison to the interstitial fluid)

• colloid osmotic (oncotic) pressure: the ratio (more in intravascular) sets up osmotic pressure that pulls fluid back into capillary

reduction in plasma proteins in luteal phase

• results in reduction in plasma colloid osmotic pressure

• less fluid pulled back into blood

• more interstitial fluid

• reduction in PV has important functional considerations

CBT and exercise

• during exercise, core body temp (CBT) rises due to heat produced by working muscles

• when CBT rises above 39°C (103°F), many body systems are compromised: drop in performance

how does body regulate CBT?

• moving the blood to the skin and offloading heat through sweat

• requires continual replenishment of body water required for perspiration and plasma volume

why do women face additional challenges in exercising?

• perturbations of the female sex hormones

• influences of hormones on fluid distribution, resting core temp, and resetting of thermoregulatory responses

high hormone phase of menstrual cycle- temperature

• baseline core temp is reset to a higher internal temp

• concomitant increase in the threshold for sweat onset

• decreased sensitivity of cutaneous vasodilation

what does the reset of temp thresholds in the high hormone phase impact?

• sweat onset, vasodilation, decreased baroreflex sensitivity

• time to critical core temperature may be reduced

• thermoregulatory control changes can compromise women’s exercise capacity (esp during heat)

plasma volume and heat

PV maintenance important for exercise performance (esp in heat)

maintained or increased PV:

• reduces viscosity of blood

• increases heat storage and transfer capacity

• increases exercising cardiac output

• increases maximal O2 uptake

maintained or increased PV does what to heat

• ability to offload heat (by virtue of increased volume of circulating fluid) is increased

• circulation to the periphery is enhanced

• but fluid balance is usually not achieved (not even when fluid availability or gastric emptying rates prevent rates of ingestion and absorption from matching sweat rates)

overall changes ~1 week before period (luteal phase)

hormones high

• bloating

• holding more fluid between cells than in the blood

• lose ~8% of plasma volume

• no biggie if not exercising

• if exercising, lose fluid available for sweat

• progesterone makes women lose total body sodium

what happens if you cant sweat?

tough time regulating body temp during exercise

• women need sodium in fluids to pull fluid into the blood

~1 week before period, progesterone makes women lose total body sodium, resulting in what risk?

leaves women more susceptible to hyponatremia than men

women salt consumption and workout

should consume ~1 teaspoon salt before long, hard, or hot workout (if weighs ~63.5 kg (140 lb))

• if weighs ~54 kg (120 lbs) should have ¾ teaspoon

men and sodium

• men do not have these sex hormone fluctuations

• little sodium would help anyone hold onto fluid than no sodium at all, but:

• men can get by with less sodium than women

overall: why do women need more sodium in fluids than men

• during exercise: TBW loss and sodium loss

• elevated sex hormones reduce resting PV by ~8% and increase sodium loss

• reduced PV and increased sodium loss means loss of power (bc reduced blood circulation)

• luteal phase affects thermoregulation more than follicular

• less heat tolerance in high hormone phase

fatigue causes

• depletion of carbs is one of the primary causes of fatigue during long sustained exercise

• most critical cause of fatigue is drop of total body water and subsequent volume loss

average adult glycogen storage

• ~300-500 g of glycogen stored in muscles

• ~75-100 g of glycogen stored in liver

• enough carb to run at moderate intensity for 20 miles

main objective of supplementing with carb during prolonged strenuous exercise

maintain blood glucose concentrations

estrogen and nutrition/exercise

estrogen is (at least partially) responsible for:

• decreased reliance on hepatic glycogen stores

• increased availability and oxidation of fatty acids

• decreased amino acid breakdown during exercise

progesterone and nutrition/exercise

• increases protein catabolism during exercise

• decreases protein synthesis during recovery

17β estradiol in exercise

• decrease hepatic glucose rate of appearance and disappearance

• decrease total oxidation

• results in relative sparing of hepatic glycogen storage during exercise

estrogen glycogen sparing in exercise

• results in less glucose available for fluid co-transport mechanisms in intestines

• less access to carbohydrates needed by muscles to perform at high intensities (thus decreased TBW and aerobic capacity)

how is water reabsorbed in the intestines?

through Na+/glucose cotransporters

it is believed that estrogen may influence estrogen metabolism how?

action on sympathetic nervous system

• reduced catecholamine release at a given intensity and workload as compared to similarly trained men

studies performed on carb depleted women show what?

• able to maintain blood glucose during follicular phase but not luteal phase

• greater effect on glycogen sparing occurs during the high hormone phase of menstrual cycle

estrogen lipid utilization

• estrogen promotes free fatty acid availability and lipid oxidation during exercise

• possibly via an increased sensitivity to the lypolytic action of catecholamines

females and intramuscular triglyceride

• intramuscular triglyceride content is dependent on dietary fat consumption

• intramuscular stores generally much larger in females than males

• utilized more in females at moderate intensity (90 min, 58% of VO2 max)

• females: larger intramuscular triglyceride stores and rely more heavily on it during exercise

sex based differences in whole body substrate oxidation during exercise

lower respiratory exchange ratio (RER) of females compared to males for a given exercise intensity and duration of exercise

amino acids difference between male/female

greater amounts of amino acids are oxidized by males during exercise than females

progesterone and protein

progesterone increases protein catabolism with less protein synthesis

• increased protein catabolism during exercise during luteal phase compared to follicular phase

• increased protein catabolism = greater excretion of urinary urea nitrogen

• higher circulating progesterone levels (or lower estrogen:progesterone ratio) promotes protein catabolism

estrogen does what to protein?

reduces protein oxidation

women and burning fat

women have a greater capacity for burning fat at a given intensity

• sparing glycogen and using less amino acids

• results in less glucose availability for fluid absorption and energy needs

progesterone effect on muscle

high levels of progesterone increase muscle breakdown

women carb consumption

• can afford to ingest lower carb grams per hour during exercise during low hormone phase

• need carb supplementation during high hormone phase

BCAAs (branched-chain amino acids)

women should ingest BCAAs (leucine, isoleucine, and valine) pre-exercise during the luteal phase to counteract progesterone’s effects, such as:

• increased catabolic effects of exercise

• blunting of protein synthesis

• increased protein degradation at rest

increased glucose availability does what?

• increase fluid balance

• improve anaerobic ability

• reducing dependence on fat as substrate → decreasing stimulus to store more fat

fat metabolism: exercise vs recovery

• women metabolize more fat during exercise

• opposite is true during recovery

women fat metabolism during exercise

• use more fat during exercise

• have greater fat stores

• increased propensity to store glycogen while maintaining a steady energy flow during exercise

women fat metabolism during recovery

• burn less fat than males during recovery

• greater ability to maintain glycaemia during recovery period following prolonged exercise

• could explain why lipolysis occurs to a lesser degree in females during this phase