Autonomic nervous system
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Autonomic nervous system. Intro. Autonomic nervous system (ANS) Sympathetic nervous system (SNS) Fight or flight Major nerve : Sympathetic chain Major neurotransmitters : Epi, NE Bind to : α and β receptors Parasympathetic nervous system (PNS) Rest and digest Major nerve : Vagus

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Autonomic nervous system

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Autonomic nervous system

Autonomic nervous system



  • Autonomic nervous system (ANS)

    • Sympathetic nervous system (SNS)

      • Fight or flight

        • Major nerve: Sympathetic chain

          • Major neurotransmitters: Epi, NE

          • Bind to: α and β receptors

    • Parasympathetic nervous system (PNS)

      • Rest and digest

        • Major nerve: Vagus

          • Major neurotransmitter: Ach

          • Binds to: Cholinergic receptors

Autonomic nervous system



Sympathetic chain

Cranial nerve X (Vagus n.)

Autonomic response to exercise

Autonomic response to exercise

  • Epi, NE increase exponentially with ex intensity

  • Effects:

    • BP

      • increase

        • Vasoconstriction

        • Increased cardiac output

    • HR

      • increase

    • Activates glycolysis/lipolysis

Training effects on autonomic nervous system

Training effects on autonomic nervous system

  • Submaximal exercise

    • Reduced catecholamine response

      • Reduced HR

      • Reduced blood pressure response

      • Reduced lactate?

      • Altered fuel use?

Training effects on autonomic nervous system1

Training effects on autonomic nervous system


  • Maximal exercise

    • Maximal adrenergic activity is increased with training

  • Effects

    • Increased maximal hepatic glucose production

  • Also

    • Helps defend blood pressure

    • Helps maintain cardiac output

Hormonal response to exercise

Hormonal response to exercise

Growth hormone

Growth hormone

  • Polypeptide hormone

    • anterior pituitary gland

      • Regulates

        • Growth (Anabolic)

          • Stimulates protein synthesis

        • Cell reproduction

        • Metabolism

          • Potent stimulator of lipolysis

      • Endocrine gland

        • Releases hormones into the blood

      • Released during

        • Fasting

        • Exercise

        • Sleep

  • Neuro-endocrine integration

    • Hypothalamic-pituitary axis

      • Hypothalamus regulates output from anterior Pituitary

        • Growth hormone releasing factor (GHRF)

Growth hormone response during exercise

Growth hormone response during exercise

  • Lag of ~ 15 minutes before GH increases

  • Proposed metabolic effects of GH

    • Increases growth of all tissues

    • Increases lipolysis

    • Promotes gluconeogenesis

    • Reduces hepatic glucose uptake

Cortisol and the pituitary adrenal axis

Cortisol and the pituitary-adrenal axis

  • Cortisol

    • Steroid hormone

      • Cholesterol

    • Glucocorticoid

      • Promotes glucose production

    • Stimulates AA release from muscle (catabolic)

    • stimulates gluconeogenesis

  • Hypothalamus

    • Releases corticotrophin releasing factor (CRF)

  • Anterior Pituitary

    • Adrenocorticotrophin (ACTH)

  • Adrenal cortex

    • cortisol

Anterior pituitary



  • Glucocorticoid

    • Cortisol/cortisone

      • Help to regulate blood glucose

      • Released during prolonged, exhaustive exercise

  • Mineralcorticoid

    • Aldosterone

      • Released from adrenal cortex

      • Works with renin/angiotensin system

      • Electrolyte homeostasis

        • Reabsorption of water and sodium, excretion of potassium



  • Note how cortisol changes throughout the day

    • also, rises to highest level at the end of exercise

    • Influenced by intensity and duration of exercise

Thyroid hormone

Thyroid hormone

  • Triiodothyronine (T3) and thyroxine (T4)

  • T3 greatest biological activity

  • Thyroid stimulating hormone (TSH; anterior pituitary) stimulates thyroid to release thyroxine

  • Cells convert T4 to T3

  • Stimulates metabolism

  • “permissive” effect

    • Enhances the effects of other hormones

    • Perhaps through adenylate cyclase/cAMP effect

Metabolic response to exercise

Metabolic response to exercise

Exercise responses

Exercise responses

  • What do these responses tell us?

  • Why measure

    • Lactate?

    • Lactate threshold?

    • Oxygen deficit?

    • Oxygen debt?

  • Quantify exercise intensity

Exercise metabolism

Exercise metabolism

  • Oyxgen consumption

    • Principle measure of exercise intensity

    • Increases linearly with intensity

  • Blood lactate

    • Easy to measure

    • Fair index of intensity

Lactate issues

Lactate issues

  • Blood lactate

    • Balance between rate of appearance (Ra) and disappearance (Rd)

    • Lactate used by other tissues as an energy source

    • Level in blood

      • Balance between Ra/Rd

      • Determined by fiber type and oxidative capacity of tissue

Muscle consumer of lactate

Muscle: Consumer of lactate

Lactate concentration

  • Blood lactate increases during exercise above lactate threshold (>45-50% Vo2max)

    • Release from tissue (muscle) greater than uptake (less active tissues)

    • Release from muscle is quite high initially, then falls

    • Some subjects actually switch to net uptake

Net Lactate release

Fate of lactate after exercise

Fate of lactate after exercise

  • Following exercise blood lactate levels fall

  • The vast majority of the Carbon from lactate (C3H5O3) shows up as expired CO2

    • Oxidized

    • C3H5O3 + H+ 3CO2 + 3H2O

  • Lactate may also be

    • Incorporated into Bicarbonate

    • Converted to glycogen

    • Converted to glucose

    • Incorporated into proteins









Expired CO2

Expired CO2

Expired CO2

Lactate turnover during exercise

Lactate turnover during exercise

  • Turnover

    • Balance between production and removal

  • Rest

    • Balance between production and removal

      • Blood lactate low

  • Exercise

    • Production greater than removal at all intensities above lactate threshold (45-50% of Vo2max)

Lactate turnover

Lactate turnover

  • Blood concentration (1) is dependent upon the balance between

    • Clearance (2)

    • Rate of appearance (3)

  • Note how trained lactate concentration is lower due to reduced rate of appearance and increased clearance rate




Endurance exercise and lactate

Endurance exercise and lactate

  • Turnover

    • Measure used when metabolite is infused

    • Turnover is then based on infusion rate/amount in blood

      • Greater clearance from blood necessitates greater infusion rate to maintain a certain level

      • Lactate turnover is increased with endurance training

  • Metabolic clearance

    • Measure of rate of disappearance from blood

    • Also increased with endurance training

Causes of the lactate threshold

Causes of the Lactate Threshold

  • Lactate threshold

    • Point where blood lactate starts to accumulate in the blood

    • Balance between Ra and Rd changes

    • MCR reaches a maximum

    • Greater recruitment of fast-twitch fibers

    • SNS?

      • Shunts blood flow away from inactive tissues

      • May reduce uptake

Oxygen deficit

Oxygen deficit

  • Oxygen deficit

    • Difference between O2 demand and O2 consumption

      • O2 demand = ATP requirement

      • O2consumption = mitochondrial ATP production

    • Energy deficit supplemented by ATP-PCr and anaerobic metabolism

    • Typically used during >LT to maximal work

    • Tough to determine during “supra-maximal” exercise, where the O2 requirement is not known

    • Component of fatigue

Oxygen debt

“Oxygen debt”

  • O2 consumption should fall back to resting levels immediately once the exercise ceases

    • This DOES NOT happen

    • Originally thought that O2 debt equal to the O2 deficit

      • Extra O2 consumption during recovery to “pay back” the debt

      • Thought to be completely due to non-aerobic metabolism (ATP-PCr and anaerobic metabolism)

  • Currently: Known that other factors help determine the size of the oxygen debt

    • Name changed to Excess post exercise oxygen consumption (EPOC)

Autonomic nervous system


STILL above resting

  • O2 consumption follows exponential decrease to resting levels

  • Time course can be quite prolonged (vs short time course of O2 deficit)

  • Temperature, catecholamines and pH impact EPOC, but have little or no effect on O2 deficit

  • So, some of the EPOC is due to oxidation of lactate/regeneration of glycogen and PCr but not a 1:1 relationship

Autonomic nervous system


  • Causes of excess post exercise VO2

    • Temperature

      • Heat production and muscle temperature increase dramatically during exercise

        • Muscle temperature can get as high as 40°C

      • High temperature can “loosen” the coupling between oxidation and phosphorylation

Epoc and mitochondrial uncoupling

EPOC and mitochondrial uncoupling

  • Fatty acids and ions

    • Fatty acids may be involved in “uncoupling” of oxidative and phosphorylation

      • brown adipose tissue of rats

      • So, heat is produced, but ATP is not

    • May also impact the permeability of Na+ and K+ across the mitochondrial memebranes

This “linkage” is affected

Epoc and mitochondrial uncoupling1

EPOC and mitochondrial uncoupling

  • Calcium

  • Increases oxygen consumption

    • Mitochondria sequester Ca2+

      • Energy dependent

    • Ca2+ uncouples oxidation and phosphorylation

Epoc and mitochondrial uncoupling2

EPOC and mitochondrial uncoupling

  • Epinephrine and Nor-epinephrine

    • Take some time to be cleared from the blood following exercise

  • pH

    • Inhibits PCr recovery

    • May make mitochondrial membrane “leakier”

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