Exercise Physiology

Describe what this graph is showing

The effects of exercise duration on energy expenditure

over time, the types of energy used is altered (more free fatty acids used at 240 than 40, while more intramuscular glycogen lipid and protein is used at 40 than 240)

describe what this graph is showing

effects of exercise intensity (VO2max) on energy expenditure

as exercise intensity increases, the body relies more on muscle glycogen for energy (vs at lower intensities, like 25%, it relies more on plasma FFA)

what are the macronutrients that are used as fuel for exercise?

carbs, fats, and proteins

types of carbohydrates?

monosaccharides- basic unit of carb (glucose, fructose, and galactose)

disaccharides- 2-10 monosaccharides bonded (sucrose, lactose, and maltose)

• glucose + fructose = sucrose, glucose + galactose = lactose, glucose + glucose = maltose

polysaccharides- three to thousands of monosaccharides (starch and fiber)

what are simple (neutral fats) known as?

triacylglycerols (triglycerides)

what are the two types of fats

saturated fats (no double bonds) - solid at room temp

unsaturated fats (one or more double bonds) - liquid at room temperature → oils

what is the function of proteins (amino acids)?

supply the body with muscle structure and function (not as much for energy)

what are the types of amino acids?

essential amino acids (need to consume in diet, don’t synthesize in body)

nonessential amino acids (synthesize in body)

what are the types of proteins

complete proteins (contains both nonessential and essential amino acids → eggs, animal products, chia seeds, soy)

incomplete proteins (don’t have all essential amino acids → vegetables; reason for pairing up foods like rice and beans in order to complete the aa’s)

what type of bonds link amino acids?

peptide bonds:

• dipeptide → 2 amino acids linked by 1 peptide bond

• tripeptide → 3 amino acids linked by 2 peptide bonds

• polypeptide → many amino acids linked together

• protein → one or more folded polypeptide chains that perform a specific function

what are the three pathways for carbs after absorption in the body?

1. energy for cellular metabolism

2. storage as glycogen in liver and muscle

3. conversion to triacylglycerol for later energy use

what is the role of carbs in the body?

1. energy fuel during intense exercise → energy derived from breakdown of blood borne glucose and muscle glycogen

• carbs are the body’s preferred fuel source during high-intensity exercise (carbs broken down into glucose → circulate blood and taken up by working muscles + glycogen - muscle storage of carbs → broken down into glucose and used to make ATP for mm contraction)

1. protein sparer → help preserve tissue protein

• when body has enough carbs available, it doesn’t have to rely on protein for energy, and saves it to be used for building / repairing tissues

1. metabolic primer/ketosis preventer → primer for lipid oxidation

• carbs help body efficiently use fat for energy and prevent excessive ketone production → carbs help ‘prime’ the pathway that allows fat to be burned efficiently

1. central nervous system fuel → primary fuel for the brain and other nerve tissues

• brain + CNS rely on glucose for fuel source

what is the role of lipids in the body?

energy source and reserve

• carries large quantities of energy per unit weight

• transports and stores easily

• provides an available energy resource

protect vital organs (brain, heart, liver)

thermal insulation

vitamin carrier and hunger suppressor

how much body mass do proteins constitute?

12-15% of body mass

what are the three main sources of body protein?

blood plasma, visceral (abdominal) tissue, muscle

what is the role of proteins in the body?

major building blocks for synthesizing tissue components like enzymes, hair, skin, and nails

what are important sources of cabs in the body

plasma glucose, muscle and liver glycogen, and conversion of other nutrients into glucose

what is glycogenesis

glucose → glycogen

what is glycogenolysis

glycogen → glucose

what is gluconeogenesis

non-carb nutrients (protein or other) → glucose

what is the primary source of energy for PA?

carbs

carbs vs lipids energy uptake

carbs generate 6% more energy than lipid per liter of oxygen uptake

what is the effect of high intensity exercise on carb vs lipid usage?

1 hr - decreases liver glycogen by 55%

2 hr almost depletes liver + muscle glycogen

what is the effect of moderate intensity exercise on carb vs lipid usage?

glycogen is the primary source in initial 20 minutes, then a mix of glycogen and lipid

what is the effect of low intensity exercise on carb vs lipid usage?

lipid is the main source with glycogen and glucose depleting over time

what are the limitations that glycogen depletion causes?

it severely limits short duration exercise performance and long duration endurance — ‘hitting the wall’

what are important sources of fat in the body for energy?

plasma fatty acids and stored triacylglycerol (triglycerides)

what is lipogenesis

creation (storage) of fatty acids (ex: glucose → fat)

what is lipolysis

breakdown of triglyceride into individual fatty acids

what percent of energy do lipids supply during PA?

30-80%

what is the primary energy source used for light moderate exercise?

intramuscular triacylglycerols and fatty acids

how does the body begin to rely more on carbs/lipids as exercise intensity varies?

light-moderate: primarily lipids

moderate: both supply equal amounts

long duration: shift to fat as primary fuel as glycogen becomes depleted

when would protein be used for energy?

protein is not a primary source of energy unless in a glycogen depleted state

what spares muscle protein from being broken down?

carbs

anabolic process

synthesis or build up of new materials

catabolic process

breakdown of materials into new materials for energy

positive nitrogen balance

nitrogen intake exceeds nitrogen excretion → new tissues are synthesized (anabolic process for muscle synthesis)

negative nitrogen balance

nitrogen intake is less than nitrogen excretion → protein broken down for energy (catabolic process for muscle loss)

what results in the use of protein for a source of energy?

prolonged exercise and glycogen depletion

what is an example of protein being used to help maintain blood glucose levels?

alanine: amino acid that can be produced by working muscle → sent to liver to be converted to glucose by gluconeogenesis → helps maintain blood glucose during exercise

what is bioenergetics?

our bodies simultaneously breaking down and building up macronutrients (CHO, fat, and protein) for energy and use depending on need

what is energy?

the capacity to do work → dynamic state related to change

what is the total energy of a system ?

potential energy + kinetic energy

what is potential energy?

relates to structure or position

potential energy is stored, and has the potential to be released and used later (like fats and carbs → when body needs energy, it breaks down these molecules and release the energy stored in their chemical bonds)

what is kinetic energy?

relates to energy of motion with release of heat

• muscles using energy to produce movement

what is the first law of thermodynamics

energy can neither be created nor destroyed, but transforms from one form to another without being depleted during the transfer process

what is the relationship between biologic work and energy transfer?

as biologic work increases, energy transfer increases

how is biologic work expressed?

mechanical measurements: Joules (J) or newton meters (N*m)

what needs to happen for biologic work to occur?

a change needs to take place. (like movement/displacement)

• if pushing on a wall, no mechanical work occurs because there is no displacement; if pushing a box five feet, mechanical work has occurred due to position change

what is bioenergetics?

flow and energy exchange within a living system

• example: energy transfer of macronutrients into useable forms of energy in the body

what are the types of reactions?

endergonic: stores energy

exergonic: releases energy

types of biologic work in humans

1. chemical- biosynthesis of cellular molecules

2. mechanical- muscle contraction

3. transport- transfer of substances among cells

how do we quantify work in humans?

newtons, joules, kilojoulse

equation for work?

work = force x distance

what is an example of energy interconversion?

cellular respiration (exergonic process)

what is an exergonic process?

macronutrient stored energy transfers in the form of ATP

• used for the mechanical work of muscle contraction, and chemical work of glycogen, triacylgerol, and protein synthesis

what are enzymes

proteins that speed up chemical reactions in the body

what are coenzymes

non protein organic substances that facilitate enzyme action by binding a substrate to a specific enzyme

effects of temp and pH on enzyme action turnover rate

enzymes operate at an optimal temp and pH

optimal temp for enzymatic rxns = 98.6 F

optimal pH = 7.4

• but varies, for instance, pepsin is found at lower pH (high acidity in stomach), and trypsin is found at higher (more basic in intestine)

enzyme action

enzyme turns on when substrate binds to active site (lock and key)

because there is a specific enzyme for a specific substrate, all unique chemical rxns in the body have a unique enzyme

enzyme inhibition

some substances inhibit enzyme activity to slow the rxn rate

competitive inhibition

substances can bind to enzyme’s active site to prevent enzyme activation

non competitive inhibitors

bind to an enzyme at a site other than the active site to change the enzymes structure and ability to catalyze the rxm

• some drugs used to treat cancer, depression, and acquired immunodeficiency syndrome are noncompetitive enzyme inhibitors

oxidation reaction

electron loss → reactions that transfer oxygen, hydrogen atoms, or electrons

reduction reaction

electron gain → reactions that allow atoms to grain electrons

oxidations - reduction reactions (redox rxns)

always occur together - coupled

• example- hydrogen traveling down a system until it can be put to use (in something like ATP)

energy metabolism is?

generating biological energy (ATP) from macronutrients

what does ATP do?

energy currency → gives us energy for any kind of action in cells

how does ATP release energy?

ATP + H2O → (release a P via ATPase) → ADP + P + 7.3 kcal/mol

what does ATP help power?

digestion, nerve transmission, muscle action, circulation, tissue synthesis

how does ATP release energy?

ATP + H2O → (release a P via ATPase) → ADP + P + 7.3 kcal/mol (energy)

ATP recycling in macronutrient breakdown

body stores 80 to 100 g of ATP in normal resting conditions, enough stored energy to power 2 to 3 seconds of maximal energy

what is a phosphorylation reaction?

chemical reaction that adds a phosphate group to another molecule

what type of reactions require ATP

anabolism (endergonic rxn)

what type of reactions release ATP

catabolism (exergonic rxn)

how is ATP produced?

aerobic (oxidative phosphorylation) and anaerobic (Substrate level phosphorylation)

aerobic (oxidative phosphylation)

occurs in mitochondria, requires oxygen, occurs at slower speed, and produces lots of ATP

main fuel is carbs and fats

anaerobic (substrate level phosphorylation)

ATP produced by directly transferring a phosphate group from a high energy substrate to ADP; occurs in cytosol, faster, no O2 required, smaller ATP yield

how much ATP is stored in body at a given time?

80-100grams, about 2-3 seconds worth

this is why ATP regeneration is so important!

phosphocreatine (PCr)

cells store 4-6x more phosphocreatine than ATP

phosphocreatine = creatine + phosphate

• phosphate can be transferred to DP to rapidly remake ATP (via creatine phosphokinase)

this happens very quickly and provides for about 10 seconds of maximal activity

this is substrate level phosphorylation

what is glycolysis

after ATP + phosphocreatine stores, body leans on glycolysis

breakdown of glucose into pyruvate

• pyruvate is turned into lactate in the cytosol (for intense exercise and immediate ATP)

• pyruvate is put through the krebs cycle during low/moderate exercise (mitochondria)

produces lactate (lactic acid) unless oxygen is present

anaerobic respiration ATP levels

generates about 5% of total ATP

(not alot but can be done very quickly → useful for sprinting / short bursts)

what types of exercise can anaerobic account for ?

sprinting at the end of an endurance run

50-100m swim sprint

100-200m running sprint

power based sports like gymnastics

aerobic respiration

oxidation (breakdown of carbs, fats, proteins → where most of our energy is generated)

90% of ATP synthesis occurs through oxidative phosphorylation

electron transport allows for ATP phosphorylation; requires oxygen as the final electron acceptor

three stages lead to release and energy conservation by cells for biologic work:

stage 1: digestion, absorption, and assimilation of relatively large food macromolecules into smaller subunits

stage 2: degrades amino acids, glucose, and fatty acid and glycerol units into acetyl-CoA

stage 3: acetyl-CoA degrades to CO2 and H2O with considerable ATP production

what are the six fuel sources that supply substrate for ATP formation?

1. triacylgycerol and glycogen molecules stored within muscle cells

2. blood glucose derived from liver glycogen

3. free fatty acids derived from triacylgerols in the liver and adipocytes

4. intramuscular and liver derived carbon skeletons of amino acids

5. anerobic rxns in the initial phase of glucose breakdown

6. PCr phosphorylates ADP under enzyme control (creatine kinase)

how do we increase PCr in muscle?

training:

• increasing muscle size can increase PCr availability

• improved oxidative capacity may increase ability to resynthesize PCr more quickly (typically takes 30 sec)

diet

• PCr is found in animal proteins (including fish)

• diets including animal protein can acquire creatine in this way, but this is not the case for vegetarian / vegan diets

dietary supplementation

• creatine monohydrate

CHO metabolism

CHO is the only macronutrient that can be metabolized anaerobicaly

CHO supplies 1/3 of total energy during light and moderate PA
CHO metabolism must occur in order for fats to be broken down for energy

aerobic CHO metabolism occurs more quickly than fatty acid breakdown

• glycogen depletion can cause reduction in exercise power

central nervous system requires constant CHO supply to function properly

rapid glycolysis

substrate level phosphorylation

quick source of energy, but not enough to sustain for long duration

final product is lactate

slow glycolysis

substrate level phosphorylation + oxidative phosphorylation

couples with citric acid cycle and electron transport chain

final product (glycolysis specific) is pyruvate

describe how glucose is phosphorylated to be converted to energy

• ‘priming the pump,’ and 2 ATP are invested to be used to phosphorylate glucose (spending ATP to be able to start making ATP)

• PFK (phosphofructokinase) → enzyme that controls how much glucose is pushed through glycolysis (rate limiting enzyme)

  • more PFK activity → glycolysis speeds up; less PFK activity → glycolysis slows down

what are the final net products of rapid glycolysis - anaerobic metabolism

2 pyruvate, 2 ATP, 2 NADH

glycogenolysis

skips glucose energy investment, goes straight from glycogen

1 less ATP required → net 3 ATP from glycolysis instead