Control of ATP in Skeletal Muscle

What is ATP

a high-energy phosphate compound which is the immediate and most direct fuel source for muscle contraction that must be continuously generated

What does the energy donor energy receiver role of ATP represent

it represents the cell’s 2 major energy transforming activities:

extract PE from food and conserve it within the bonds of ATP

extract and transfer the chemical energy in ATP to power biological work

What are the 3 interconnected metabolic pathways in muscle cells that are responsible for mating ATP supply to demand at rest and during exercise

ATP-PCr or Phosphagen system (anaerobic alactic)

Glycolysis

Oxidative Phosphorylation

What occurs during the ATP-PCr system

formation of ATP via degradation of phosphocreatine, it doesn’t produce lactic acid and doesn’t require oxygen

how much ATP does the body store under normal conditions

it only stores 50-100g of ATP at any time which is enough to power several seconds of explosive, all out activity (up to 10 sec)

What happens to overcome the storage limitation of ATP-PCr

ATP synthesis proceeds uninterrupted to continuously supply energy for all the body’s biological work from carbs and fat and phosphocreatine

what is phosphocreatine

it is another intracellular high-energy phosphate compound and cells store 4-6 times more PCr than ATP

what happens during the kinase reaction

creatine is phosphorylated to PCr by ATP during rest and the reaction flips during exercise

What are the characteristics of the phosphagen system dynamics

extremely rapid reaction, extremely sensitive to ATP demand, reaction catalyzed by enzyme, creatine kinase

what is the role of the phosphagen system dynamics

supply ATP at the onset of exercise at extremely high rates for high power output activities, energy buffer while other ATP systems are “turned on” so that ATP levels stay stable

what is a limitation of the phosphagen system dynamics

limited “substrate”, including stored ATP and intracellular PCr, which means we run out of energy supply very quickly (5-10s) but it gets restocked during rest of low intensity exercise

what is the phosphagen system efficiency limited by

it is limited by the amount of PCr stored in muscle and the speed at which it can regenerate ATP

What are strategies to optimize the function of the phosphagen system efficiency

creatine monohydrate supplemention

it is the most studied supplement that can increase phosphocreatine stores, make you perform longer and have better recovery and can enhance sleep and help with cognition and muscle preservation

what does HIIT do to the phospagen system efficiency

it stresses the system and makes the body adapt and recovery faster

what does rest and recovery do to the phosphagen system

it helps to restore creatine levels (rest 4 min for max lifts)

what does strength and power training do for the phosphagen system

it improves the ability for the system to rapidly deliver ATP and more muscle means more storage

What is glycolysis (anaerobic lactic)

it is the formation of ATP via degradation of glucose from glycogen and is the second fastest way to generate ATP and lasts from 10-120 seconds of activity

what happens during glycolysis

2 forms of carbohydrate breakdown to occur in a series of fermentation reactions, lactate and pyruvate

what are the characteristics of lactate

it is formed by pyruvate, it is the anaerobic part of glycolysis, it is rapid but limited ATP production and occurs when oxygen supply can’t keep up with ATP use, which creates lactate

What are the characteristics of pyruvate

it is the aerobic part of glycolysis, it occurs in the mitochondria, it is slow but has substantial ATP production, occurs when oxygen is available and produces more ATP than the ETC

when is glycolysis dominant

it is dominant is activities like the 400m sprint, stair climbs, or a hard hockey shift

Does the glycolytic process from glucose to lactate or pyruvate involve oxygen

no, it doesn’t involve oxygen

What are the steps of glycolysis

energy investment phase

energy generation phase

if energy demand is high and oxygen can’t keep up then pyruvate is converted to lactase and NAD+ and glycolysis will occur again

where does glycolysis occur

it occurs in the watery medium inside the cell, outside the mitochondria

When is pyruvate reduction to lactate crucial

it is crucial during NADH accumulation, when demand for energy is high

what are the products of glycolysis

2 ATP, 2 NADH, 2 pyruvate

where is muscle glycogen stored

its stored locally and is a rapid fuel source during high intensity exercise

where is blood glucose stored

it comes from the liver or recent meal, supports longer exercise

which is more efficient, glycogen or glucose

glycogen, it produces 3 ATP while glucose produces 2

What do muscles prefer during short intense exercise

they prefer glycogen

What are the characteristics of the fate of pyruvate during glycolysis

occurs in sarcoplasm and has a very rapid rate of ATP production

has energy “investment” phase, 2ATP from glucose and 1 ATP from glycogen used to add phosphate to glucose and fructose 6 phosphate

has energy “generation” phase: net gain of glycolysis is 2 ATP if glucose is the substrate and 3 ATP if glycogen is the substrate

what is the role of the rate of pyruvate during glycolysis

supply ATP at high rates for high power and output activities

supply ATP in absence of adequate ATP via oxidative phosphorylation

first step in aerobic degradation of carbs: supplies NADH to the ETC

what is the limitation of pyruvate during glycolysis

acidosis is the limitation (increase H+ or decrease pH)

what is the lactate threshold

the exercise intensity at which lactate begins to accumulate in the blood at a faster rate than it can be cleared, athletes can train it to become more efficient and can improve lactase clearance to delay the offset of fatigue

when is the first lactate threshold

it is at the beginning of high intensity

what is the fate of pyruvate during aerobic conditions

2 pyruvate enter mitochondria via the mitochondrial pyruvate carrier

converted to acetyl-CoA by the pyruvate dehydrogenase complex

generates 2 NADH

Acetyl-CoA enters the Krebs cycle

pyruvate is converted to 2 acetyl-CoA, 2 NADH, 2 CO2

what is oxidative phosphorylation (aerobic metabolism)

formation of ATP by the use of oxygen, takes more time to turn on, but is unlimited in its capacity

What are the steps of the Kreb cycle

Inputs: Acetyl-CoA, NAD+, FAD, GDP, Pi

outputs: 3 NADH, 1 FADH 2, 1 ATP, 2 CO2

role: supplies NADH and FADH 2 to the ETC

oxygen not used during the cycle

What is the first step of ETC

Complex 1 and 2: NADH and FADH transfer energy in form of electrons to ETC

complex 1 pumps protons from mitochondrial matrix into the inter membrane space to create a proton gradient

complex 2 donated and passes electrons

both transfer electrons to coenzyme Q which carry them forward reducing it to ubiquinol

what is the second step of ETC

complex 3: receives and transfers electrons to cytochrome c which pumps more H+ into inter membrane space

Cyt c: shuttles electrons to complex 4

Complex 4 transfers electrons to O2 which forms H2O

the proton gradient is maximized to drive ATP synthase

What is ATP synthase

an enzyme complex consisting of F0 region where protons flow through, F1 region which is the ATP synthesis site

What are the types of fast twitch fibers

2a: pink, moderate aerobic capacity, fatigue resistant

2x: white/pale, very low aerobic capacity

what are the characteristics of fast twitch fibers

rapid contraction speeds, high capacity for anaerobic ATP production via glycolysis but is short term

what are the characteristics of slow twitch fibers

slower contraction speeds, rely on oxidative metabolism, high mitochondria content which gives efficient ATP production, high fatigue resistance and lactate threshold, red

what is the average fiber type distribution

type 1: 45-55%

type 2a: 30-35%

type 2x: 10-20%

distribution varies by muscle group

what are the only muscle fibers that grow

type 2x fibers are the only ones

What does adrenaline do during exercise

it enhances glucose uptake in muscle, independent of insuling

increase glycogen breakdown

increase lipolysis by activating hormone-sensitive lipase in adipose tissue

what occurs during aerobic training adaptation

increase mitochondrial density and biogenesis

increase capillary density

increase oxidative enzymes which improve fat and carbo oxidation, and increase lactate threshold

what occurs during anaerobic training

increase glycolytic which leads to faster ATP from glucose

increase muscle buffer capacity which tolerates high H+

increase PCr recovery rate via aerobic adaptations in mitochondria

what is anaerobic power

the max rate at which energy can be produce by the body’s anaerobic energy system and anaerobic glycolysis

measure of how quickly the body can generate energy without relying on oxygen

what is anaerobic capacity

the total amount of energy that can be produced by the body’s anaerobic energy systems during a sustained high intensity activity.

represents the ability to maintain high power output over a period of time, relying on anaerobic pathways