KIN 346 Exam 2

How is ATP regenerated?

it is continually rebuilt from ADP + Pi

Which energy system pathway dominates?

the contribution depends mainly on intensity, duration, fuel, and oxygen availability

With regards to hormones, how is fuel mobilized or stored?

Exercise generally increases fuel mobilization and changes insulin/glucagon balance

Key measures of how much energy is being used?

VO2, VCO2, calorimetry, RER, and VO2 max

With regards to fatigue, why does performance fall?

Fatigue is multifactorial and reversible with rest

What changes with training?

Aerobic training improves oxygen delivery/use; anaerobic gains rely heavily on neural, strength and buffering changes

ATP Hydrolysis

ATP → ADP + Pi; releases usable energy for processes such as myosin cross-bridge cycling

Bioenergetics

The study of how energy is transferred and used in biological systems

Catabolism

Breakdown of molecules to release energy

Anabolism

Building larger molecules from smaller units; generally requires energy

Oxidation/Reduction

Oxidation = loss of electrons; Reduction = gain of electrons. ETC reactions alternate these processes.

Enzyme

protein that speeds a chemical reaction without being consumed

Rate-limiting enzyme

Enzyme that exerts major control over the speed of a pathway

Phosphorylation

Addition of a phosphate group; in energy metabolism, it can help form ATP or activate intermediates

Glycogenesis

Formation/storage of glycogen from glucose

Glycogenolysis

Breakdown of glycogen

Gluconeogenesis

Formation of glucose from non-carbohydrate sources including lactate, glycerol, and amino-acid carbon skeletons

Proteolysis/Protein synthesis

breakdown of proteins into amino acids / formation of body proteins from amino acids

Fuel Storage

• carbs stored primarily as glycogen in skeletal M and liver

• fat stores mainly as triglyceride (TG), a TG contains 3 fatty acids + glycerol

• amino acids are the building blocks of proteins & can contribute to metabolism, especially during prolonged exercise or low carb availability

Energy Systems & Muscle Metabolism

all 3 systems operate at the same time. the key issue is which system contributes the greatest share of ATP at a given moment.

System: ATP-PCr

• primary fuel/rxn: stored ATP & phosphocreatine (PCr) regenerate ATP via creatine kinase

• O2?: no direct O2 requirement

• speed/capacity: fastest; very limited stores

• best associated w: maximal efforts lasting roughly seconds

System: Glycolysis

• primary fuel/rxn: glucose or glycogen → G6P → Pyr; Pyr may become lactate

• O2?: can proceed w/out O2

• speed/capacity: fast; limited by substrate, H+, and other factors

• best associated w: high intensity efforts lasting seconds to minutes

System: Oxidative

• primary fuel/rxn: Acetyl-CoA enters Krebs cycle; NADH/FADH2 deliver electrons to ETC; oxidative phosphorylation makes ATP

• O2?: yes

• speed/capacity: slowest ATP rate; greatest capacity

• best associated w: longer duration, lower-to-moderate intensity work

ATP-PCR System

• ATP hydrolysis supplies immediate energy. PCr donates its phosphate to ADP to rapidly rebuild ATP.

• Creatine kinase is the key enzyme: PCr + ADP + H+ ↔ ATP + creatine.

• PCr formation occurs in the mitochondria when ATP supply is adequate; PCr is then available in the cytosol for rapid ATP regeneration.

• The system is powerful but short-lived because intramuscular ATP and PCr stores are small.

Glycolysis & Pyruvate fate

• The usable carbohydrate form entering glycolysis is glucose-6-phosphate (G6P). Glycogen can enter glycolysis after being broken down and phosphorylated.

• Glycolysis occurs in the cytosol and ends with pyruvate. Its rate-limiting enzyme is phosphofructokinase (PFK).

• Pyruvate fate depends on exercise intensity, oxygen delivery/use, mitochondrial capacity, and the balance between production and clearance: it can become lactate or be converted to acetyl-CoA.

• Lactate is not simply a waste product; it can be transported and oxidized or converted back to glucose in the liver through the Cori cycle.

Oxidative Metabolism

• Pyruvate is converted to acetyl-CoA before entering the Krebs (citric acid) cycle.

• The Krebs cycle produces NADH and FADH2. These electron carriers deliver electrons to the electron transport chain.

• The ETC uses a series of oxidation-reduction reactions to create a proton gradient. ATP synthase uses that gradient to form ATP: oxidative phosphorylation.

• NADH produces approximately 2.5 ATP and FADH2 approximately 1.5 ATP.

Carb and Fat Metabolism

Fuel selection shifts with intensity: as exercise intensity rises, the body generally shifts from a greater reliance on fat toward a greater reliance on carbohydrate. This is the crossover concept.

Carbohydrate pathway: Glycogenolysis

Glycogen → glucose-related intermediates; supports blood glucose or muscle energy.

Carbohydrate pathway: Glycolysis

G6P → pyruvate; produces ATP rapidly and can proceed without direct oxygen use.

Carbohydrate pathway: Gluconeogenesis

Lactate, glycerol, and amino-acid substrates → glucose, primarily in the liver.

Carbohydrate pathway: Cori cycle

Lactate from muscle travels to liver, is converted to glucose, and glucose can return to muscle.

Carbohydrate pathway: Glycogenesis

Glucose → glycogen for storage, especially when insulin is elevated.

Fat Metabolism

• Lipolysis is the breakdown of triglycerides into fatty acids and glycerol.

• Fat circulating in the blood is commonly transported as free fatty acids (FFAs).

• Beta-oxidation converts fatty acids into acetyl-CoA, which enters the Krebs cycle.

• A triglyceride has three fatty acids; complete oxidation therefore includes ATP from all three fatty acids plus ATP from glycerol. The slides use an example of about 406 total ATP for a triglyceride under their accounting assumptions.

Protein Metabolism

• Proteolysis breaks body proteins into amino acids.

• Amino acids may be used for protein synthesis or contribute carbon skeletons to energy metabolism after removal/processing of nitrogen

Hormone: Insulin

Class/source: nonsteroid; pancreas

Major exercise-related effects: Promotes glucose uptake, glycogen storage, fatty-acid uptake/triglyceride storage, and amino-acid uptake; inhibits liver gluconeogenesis.

Hormone: Glucagon

Class/source: nonsteroid; pancreas

Major exercise-related effects: Released especially when blood glucose is low; promotes liver glycogenolysis and gluconeogenesis

Hormone: Epinephrine/norepinephrine

Class/source: Amino-acid-derived catecholamines; adrenal medulla

Major exercise-related effects: Sympathetic activation; increases liver and muscle glycogenolysis and lipolysis.

Hormone: Cortisol

Class/source: Steroid glucocorticoid; adrenal cortex

Major exercise-related effects: Increases amino-acid mobilization for gluconeogenesis, glycogen breakdown, and lipolysis; anti-inflammatory.

Hormone: Growth Hormone

Class/source: Peptide; anterior pituitary

Major exercise-related effects: Increases lipolysis and liver gluconeogenesis; supports post-exercise muscle growth.

Hormone: T3/T4

Class/source: Amino-acid-derived; thyroid

Major exercise-related effects: Increase BMR, glucose uptake, glycolysis/gluconeogenesis, and lipid mobilization; support proper action of other hormones.

Hormone: ADH

Class/source: Peptide; posterior pituitary

Major exercise-related effects: Supports water conservation and plasma-volume regulation during fluid loss

Hormone: Aldosterone

Class/source: Steroid; adrenal cortex, RAA system

Major exercise-related effects: Promotes sodium retention; water follows sodium, supporting blood/plasma volume.

Steroid vs. Nonsteroid hormones

• Steroid hormones are derived from cholesterol, are lipid-soluble, and can diffuse through cell membranes to influence intracellular receptors and gene expression.

• Nonsteroid hormones are not lipid-soluble and cannot cross the cell membrane freely. They act through membrane receptors and intracellular second-messenger pathways. They include protein/peptide and amino-acid-derived hormones.

High-yield hormone patterns

• During exercise, sympathetic hormones rise and fuel mobilization increases.

• As exercise intensity or duration increases, growth hormone release generally increases.

• Aerobic training can reduce catecholamine levels at the same absolute exercise intensity because the exercise is less physiologically stressful.

• The endocrine system is regulated by feedback loops. Negative feedback occurs when the response reduces the original stimulus, helping restore a stable internal condition.

Energy Expenditure

Energy expenditure is the rate at which the body uses energy. A food “Calorie” is a kilocalorie (kcal), the heat required to raise 1 kg of water by 1°C.

Direct calorimetry

What it tells you: Heat produced by the body

Strengths & Limits: Accurate over time and useful at rest; expensive, slow, and affected by exercise equipment and sweat

Indirect calorimetry

What it tells you: Energy expenditure estimated from respiratory gases

Strengths & Limits: Uses O2 consumption and CO2 production; best during steady-state oxidative metabolism

VO2

What it tells you: Volume of oxygen consumed per minute

Strengths & Limits: Inspired O2 volume minus expired O2 volume; central measure of aerobic metabolism.

VCO2

What it tells you: Volume of CO2 produced per minute

Strengths & Limits: Expired CO2 volume minus inspired CO2 volume.

RER

What it tells you: VCO2 / VO2

Strengths & Limits: Helps estimate carbohydrate-versus-fat use; values trend higher with greater carbohydrate use.

VO2max

• VO2max is the point at which oxygen consumption no longer increases despite further increases in exercise intensity. It is the best single measure of aerobic fitness, but not necessarily the best predictor of endurance performance.

• VO2max may be reported as L/min (absolute) or ml·kg−1·min−1 (relative to body mass). Relative VO2max allows fairer comparisons among people of different body sizes, especially for weight-bearing activities.

Lactate Threshold

• Lactate threshold is the intensity at which blood lactate accumulation markedly increases because production exceeds clearance. It reflects interaction of aerobic and anaerobic metabolism and is commonly expressed as a percentage of VO2max.

• Typical lactate-threshold values of about 50–60% VO2max for untrained people and 70–80% for trained people.

Fatigue

Fatigue is a decrement in muscular performance with continued effort accompanied by tiredness, or the inability to maintain the required power output at a given intensity. It is reversible by rest.

Excess post-exercise oxygen consumption (EPOC)

• Replenishes ATP and PCr stores.

• Supports continued substrate cycling of glucose and fatty acids.

• Maintains an elevated rate of fatty-acid oxidation.

• Helps return elevated body temperature toward normal.

• Reflects elevated catecholamine levels and other recovery processes

Adaptations to Training

Training adaptations are specific to the systems repeatedly stressed. Aerobic training primarily improves oxygen delivery and aerobic ATP production; anaerobic training improves high-intensity performance through several mechanisms.

Aerobic training adaptation: Increased capillary density

Functional result: Greater oxygen delivery to active skeletal muscle.

Aerobic training adaptation: Increased myoglobin concentration

Functional result: Greater oxygen transport/storage within muscle and improved delivery to mitochondria.

Aerobic training adaptation: Increased mitochondrial density

Functional result: Greater capacity for aerobic ATP production.

Aerobic training adaptation: Increased oxidative capacity

Functional result: Faster rate of aerobic ATP production.

Aerobic training adaptation: Higher lactate threshold

Functional result: Can exercise at a higher percentage of VO2max before substantial lactate accumulation; reflects improved production and clearance.

Aerobic training adaptation: Greater fat oxidation / lower submaximal RER

Functional result: More ATP can be produced through beta-oxidation, reducing reliance on glycolysis at a given submaximal workload.

Aerobic exercise prescription

• Frequency: approximately 3–5 days per week.

• Duration: approximately 20–30 minutes per day.

• Intensity: the most important factor; the textbook recommendation shown is about 70% VO2max.

• The muscle must be active and performing work for local adaptations to occur.

Stroke Volume

• volume of blood pumped in one heartbeat

• SV = EDV - ESV

EDV

volume of blood in the left ventricle before the heart contracts

ESV

volume of blood when the heart contracts (left over)

Cardiac Output (Q)

• total volume of blood pumped per minute

• Q = HR x SV

3 major functions of blood

• transport (O2, nutrients, waste)

• temp regulation

• pH balance

blood volume

• 5-6L in men

• 4-5L in women

whole blood

plasma + formed elements (blood cells)

hematocrit

total percent of volume composed of formed elements

red blood cells

• male: 42-45%

• female: 38-42%

anemia

less blood cells make you anemic

At rest where is most of the blood?

in the veins

When at rest:

large resorvior of blood is in the splanchnic region

When exercising:

blood moves out of the splanchnic region to the needed muscle

intrinsic control of blood flow

ability of local tissues to constrict or dilate arterioles

Intrinsic Control of Blood Flow

• occurs through capillary beds

• changes occur because M is contracting

• Metabolic mechanisms (VD):

buildup of local metabolic by-products

uses O2, produces, CO2, K+, and H+

Extrinsic Neural Control of Blood Flow

• when the sympathetic system gets activated, releases Epi & Norepi which causes catecholamines to bind to receptors and causes smooth M to contract

• Redistribution of flow at organ, system level

• sympathetic nervous system innervates smooth M in arteries and arterioles:

Baseline sympathetic activity → vasomotor tone

During exercise: increases sympathetic activity → increases vasoconstriction

At rest: decreases sympathetic activity → decreases vasoconstriction (passive VD)

Mechanisms that assist venous return

• one-way venous valves

• muscle pump

• respiratory pump (big changes in thoracic pressure, so big breaths during high intensity exercises)

What system regulates HR

nervous system

HR graph

• linear relationship

• at rest: total activation of PNS

• 0-100bpm: gradual withdraw of PNS

• 100bpm to HR max: gradual increase of SNS

Stroke Volume Graph

venous return and EDV are increasing meaning more blood is going to the heart. more blood into the left ventricle stretches the left ventricle resulting in more forceful contractions (Frank - Starling Mechanism) and thus a decrease in ESV. However, because the heart size (LVEDD) is fixed (it can only get so big) and blood volume is limited, at 60% VO2 max there is a plateau.

LVEDD

left ventricle end diastolic diameter

Cardiac Output Graph

• HR = linear relationship

• SV = plateau

• from rest to 60% VO2 max: HR and SV increasing

• from 60% VO2 max to max: only HR increasing

SBP (systolic blood pressure)

determined by increase in Q (cardiac output) x decrease in TPR (total peripheral resistance)

a-VO2 difference

As exercise increases:

• arterial content increases

• venous content decreases

• a-VO2 difference increases

this is because more muscle mass is being recruited which means we need more oxygen

1g of Hb carries

1.34mL of O2

Hb in male and female

male: 15g of Hb/100mL of blood

female: 12.5g of Hb/100ml of blood

to find O2 in blood

multiply grams of Hb by 1.34

example for males: 15 × 1.34 = 20.1 mL of oxygen/ 100mL of blood

Bohr effect

pH and temp can affect how O2 binds to Hemoglobin

• lower pH or higher temp results in more O2 being released from hemoglobin which makes O2 get delivered faster and ATP production faster

3 ways CO2 is carried in blood

• bicarbonate

• dissolved in plasma

• bound to Hb (carbaminohemoglobin)

bicarbonate

• transports 60-70% of CO2 in blood to lungs

• carbonic acid dissociates into bicarbonate (CO2 + H2O → H2CO3 → HCO3- + H+) rxn is catalyzed by carbonic anhydrase

• when CO2 gets into lungs, the rxn goes the other way and CO2 is produced

dissolved carbon dioxide

• not very efficient

• 7-10% of CO2 dissolved in plasma

• when PCO2 is low in the lungs, CO2 comes out of solution and diffuses into alveoli

Carbaminohemoglobin

• 20-33% of CO2 transported bound to Hb

• does not compete w O2-Hb binding since O2 binds to heme portion of Hb and CO2 binds to protein (globin) portion Hb

• getting into lungs: increase in PCO2 → easier CO2-Hb binding

• leaving lungs: decrease in PCO2 → easier CO2-Hb dissociation

avg amount of O2 per 100mL of blood

20mL of O2

Pulmonary ventilation in relation to exercise intensity

• Ventilation increases before exercise starts due to anticipating & preparing for the exercise (ex: a swimmer or runner waiting for the beeper to go off before starting)

• As intensity of exercise increases, so does pulmonary ventilation

• Ventilatory rate gets closely matched with the amount of muscle mass in intensity

Pulmonary Diffusion

100% AIr = 79.04% N2 + 20.93% O2 + 0.03 CO2
- Total air P: atmospheric pressure
- individual P: partial pressures
Standard atmospheric P = 760 mmHq
- Daltons Law: total air p = PN2 + PO2 + PCO2
- PN2 = 760 x 79.04% = 600.7 mmHg
- PO2 = 760 x 20.93% = 159.1 mmHg
- PCO2 = 760 x 0.04% = 0.2 mmHg

Regulation of Pulmonary Ventilation

- Primary drive to increase ventilation during exercise (starts in the brain, motor cortex) --> goes into higher brain centers --> Ventilatory control center (Medulla Oblongata) (Peripheral chemoreceptors and Skeletal muscle receptors (chemo receptors and mechanoreseptos that provide feedback for ventilation) also go into control center) --> the control center then goes into respiratory muscles

Central Mechanisms of regulation

Respiratory centers
- inspiratory, expiratory centers
- located in brain stem (medulla oblongata, pons)
- Established in rate, depth of breathing via signals to respiratory muscles
- Cortex overrides signals of necessary
Central chemoreceptors
- stimulated by increase in CO2 in cerebrospinal fluid
- increase rate and depth of breathing, remove excess CO2 from body

Peripheral Mechanisms of Regulation

peripheral chemorceptors (prevents you from stopping your breathing)
- in aortic bodies, carotid bodies
- sensitive to blood PO2, PCO2, H
Mechanoreceptors (stretch)
- in pleaurae, bronchioles, alveoli
- excessive stretch--> reduced depth of breathing
- Hering - Breuer reflex