energy metabolism

where does our energy come from

carbs, lipids and protein converted to ATP for energy

ATP can be generated by

ADP + PC > C +ATP, anaerobic respiration/glycolysis, or aerobic respiration (maintaining blood glucose is critical)

carbohydrates

preferred fuel source of body for max activity, less O2 required compared to fat, only substrate that can be used in anaerobic metabolism

glucose

simple CHO (what we break down from carb sources of food)

1g glucose =

4kcal of energy

normal fasting blood glucose

80-100

normal blood glucose after eating

170-200

normal blood glucose 2-3 hours after eating

120-140

plasma glucose

only substrate that can be used by the brain or RBCs for energy

glucose in excess is

cytotoxic - dont want too much of a good thing

hemorrhagic stroke

blood interaction in brain allows glucose to kill brain cells, downstream is not perfused so no glucose

ischemic stroke

not perfused, getting no glucose or O2 and no aTP production is possible

CHO that is not used or circulating is

stored as glycogen in the muscle or liver (more in muscle - about 400g muscle 100g liver)

with a 24 hour fast

it would be expected to dip into glycogen stores

glycogenesis

formation of glycogen from glucose via glycogen synthase stimulated by eating

is CHO is not circulated or stored, it is

converted to adipose tissue

glycogenolysis

breakdown of glycogen to glucose via glycogen phosphorylase, stimulated by EPI, glucagon, and cA2+ released with muscle contraction

gluconeogenesis

creation of glucose from non-CHO sources, stimulated by depletion of glycogen stores or protein breakdown (why fasting decreases muscle mass), can use backbone of triglyceride, pyruvate or lactate

role of CHO in the body

energy source, protein sparer, primer for fat catabolism

lipids

long hydrocarbon chains, insoluble in water

lipids are found where in the body

intramuscular, circulating in blood as FFA, stored as adipose tissue, or as circulating triglycerides/lipoproteins (10%)

triglyceride

simple lipid, glycerol backbone with 3 fatty acid chains - major storage compound for lipids, # of carbons they have determine how much energy they will produce

enzymes that catalyze breakdown of triglycerides

adipose triacylglycerol (ATGL) and hormone sensitive lipase (HSL)

glycerol

soluble in blood, can enter glycolysis in cytoplasm, not typically in skeletal muscle, can be converted to glucose in liver

free fatty acids

must be bound to albumin to be transported in blood, receptors in muscle cell membrane bring FFA into cytoplasma then they're translocated or transported into mitochondria

beta oxidation

cyclic series of steps that breaks off successive pairs of carbon atoms from FFA which are used to form acetyl CO A

role of lipids in the body

energy source and reserve (primary source at rest or with lower intensity exercise - 90% of total energy), protects vital organs, thermal insulation, vitamin carrier

1g fat

9kcal energy

fat is stored

dry

when CHO availability is inadequate

oxaloacetate is converted to glucose, Acetyl CoA cant enter krebs without oxalocetate, so liver converts Acetyl CoA into ketones

ketones can be used as

fuel by muscles, nerves and brain - but accumulation increases acidity and puts body into ketosis which can disrupt physiological function (decrease enzyme function, etc)

proteins

chains of amino acids - 20AAs that we need that can form >80000 proteins

complete proteins

have all 20AA's, 8AA's can be produced by the body, 12AA's have to be gotten through dietary intake (essential)

AAs are never

stored - body is always using them for something

role of protein in the body

structural components, cellular transporters, enzymes, blood clotting, form contractile appratus of muscle, energy (if using for energy, stealing it from another function)

1g protein

4kcal energy

ATP is a universal

energy donor - in energy requiring and energy yielding reactions

coupled reactions

energy required and energy releasing

ADP to ATP takes

7kcals of energy

ATP gets broken down via

ATPase

ATP supply

enough for a 6 sec sprint, not a lot stored, must be constantly producing for demand (depletes but never drops because of constant reproduction)

ATP production in the mitochondria

citric acid cycle/electron transport chain uses fatty acids, pyruvate from glucose, deaminated AA's

ATP production in the cytosol

glycolysis/anaerobic, phosphocreatine, glucose/glycogen, glycerol, deaminated AA's

daily ATP production is a combination of

high production at a slow rate, low production fast rate

high production at slow rate is

aerobic metabolism

low production at fast rate is

anaerobic metabolism

three energy systems

phosphagen system, anaerobic glycolysis, aerobic

phosphagen system

ADP and PCr converting to ATP and creatine via creatine kinase

ATP-PC provdes

immediate energy supply for the first 10-15sec

glycolysis becomes the primary energy supply

about 10 sec in

aerobic is dominant energy supply

at 90 seconds onwards

time-energy system continuum

50/50 aerobic and anaerobic contribution of energy at 75 sec

alactic anaerobic metabolism

body can store 90-160mmol/kg in muscle of creatine in dry muscle (reversible), creatine broken down to creatinine (irreversible)

95% of creatine stroage is in

muscle

glycolysis is stimulated via

insulin, EPI, presence of AMP and ADP

glycolysis is inhibited by the

presence of ATP, low pH and citrate

anaerobic glycolysis converts six carbon molecule

2 three carbon molecules

oxidation-reduction reactions

oxidation of glucose, takes an H off and allows NAD+ to form with the e- and make NADH via reduction

glucose oxidation byproduct is

pyruvate

oxidation

loss of hydrogen/electrons in several intermediary steps in cellular respiration

electron donors

organic fuels

nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD)

2 most important hydrogen carriers in cellular respiration, can accept 2 electrons and 2 protons from 2 H atoms

FAD binds with

both H atoms to form FADH2

NAD+ is the

more important H carrier in human metabolism

pyruvate turns into

acetyl CoA when exposed to oxygen, and lactate without oxygen

lactate dehydrogenase

responsible for lactate production from pyruvate with no O2 present, and when NADH is present to donate the E to make lactate

at rest, lactate and pyruvate levels in the body are

at equal amounts

lactic acid at physiological pH

is broken down almost immediately into H and La - constant production of lactic acid in the body is always occuring and increases during anaerobic metabolism to fuel exercise performance

before lactate begins to accumulate, it either

is converted back to pyruvate with sufficient O2 and NADH present, or it diffuses out of the muscle to be buffered in the blood or interstitial fluid

lactate clearance is via

transamination, sweat, stays circulating as resting lactate level, oxidation (primary)

transamination

forms keto acids and amino acids

intracellular lactate shuttle

MCT1 moves lactate between cytoplasm and mitochondria, lactate oxidized in mitochondria to pyruvate for aerobic metabolism

extracellular lactate shuttle

MCT1/4 moves lactate in and out of tissues - either out of FOG/FG and into SO or into cardiac muscle or liver via bloodstream

lactate can also be involved in the liver via

cori cycle doing gluconeogenesis to create glucose as a nonCHO

intense exercise leads to lactate accumulation becauce

anaerobic is working quickly

lactic acid production is via

muscle contraction, enzyme activity and based on muscle fiber type

muscle contraction causes

Ca2+ release from SR activating glycogen phosphate which facilitates glycogenolysis and produces lactate

lactic dehydrogenase

(converts pyruvate to lactate) highest rate of function of all glycolytic enzymes, increased pyruvate and NADH means greater LDH activity, maintaining the redox potential to keep cell glycolysis going (making H available, etc)

pyruvate dehydrogenase

converts pyruvate to acetyl coa

fast glycolytic muscle fibers rely on

glycolysis (because non oxidative) - resulting in lactic acid production, LDH enzymes are predominant in FG fibers too (facilitating conversion of pyruvate to lactate)

sympathetic neurohormonal activation for lactic acid production

increased EPI and glucagon causes decreased insulin and increased glycogen breakdown which increases G6P which increases rate of glycolysis leading to increased pyruvic acid production and eventually lactic acid production

insufficient oxygen levels

O2 not available in mitochondria as final e acceptor in ETS so cell must rely on anaerobic glycolysis leading to lactic acid production

lactate accumulation is caused by

decreased redox potential, increased activcation of fast twitch muscle fibers and rate of lactae production exceeding removal

lactate threshold

exponential increase in lactate threshold where production exceeds clearance, usually at about 50% Vo2max (higher in atrained athlete)

good aspect of lactic acid

used for energy n slow twitch fibers, for gluconeogenesis, cardiac cycle, takes H- with it when it leaves the cell eventually allowing pH to drop which shifts the O2 curve and permits more O2 into cell to allow aerobic metabolism

lactic acid does not cause

DOMS

lactic acidosis

decreased pH will decrease enzyme function, and pulmonary patients will struggle because lungs are a buffer for lactate

lactic acidosis can be a predictor of

mortality (increased blood lactate = increased risk of death)

normal blood lactate

hyperlactemia

2-4mmol/m

severe lactic acidosis

>4mmol/m (increases mortality)

lab procedures to measure anaerobic metabolism

ATP-PC and lactate blood tests, wingate anaerobic test (gold standard), stair climb, vertical jump, etc.

variance in females vs males for anaerobic characteristics

males have more stored PCr due to more muscle mass, and accumulate more lactate in adulthood due to testosterone (no difference when you normalize to muscle mass)

when you normalize to lean body mass, mechanical power and capacity

is basically equal between males and females

anaerobic characteristics of children

slightly lower availability and utilization of PCr, less lactate accumulation than adults but rate of clearance is similar, lactate threshold occurs at a higher % of VO2max because lower anaerobic capacity and more reliance on aerobic metabolism, lower mechanical power and capacity

muscle enzyme theory for children

producing less but oxidative enzymes are more robust

muscle characteristics theory for children

more FOG (type 2A) which means less lactate production (FG produces the most)

sexual maturation theory for children

teststerone influences muscle mass - increases with puberty

neurohormal regulation theory for children

decreased NS and endocrine activation with exercise (liver is better at gluconeogenesis because more bloodflow)

anaerobic characteristics of older adults

less ATP-PC stores but increased ADP/creatine in muscles, lower lactate accumulation at relative workloads (higher at absolute workloads because working harder), lower max lactate levels, lactate threshold at higher %vo2max, less mechanical power and capacity