Exercise Metabolism 101: How do we fuel physical activity?

What is the muscle contraction cycle?

- A signal travels along the nerves to the neuromuscular junction, which

releases a neurotransmitter - acetylcholine

- This creates a signal that affects the sarcolemma and travels down the T

tubules and causes a release of Ca2+ from the sarcoplasmic reticulum

- Ca2+ binds to troponin, which causes the tropomyosin to change

configuration, which then exposes the myosin binding site on actin

- A contraction occurs with energy obtained from the hydrolysis or use of

ATP bound to myosin, which is then released as ADP + Pi

- The re-binding of ATP relaxes the myofibril, releasing myosin

- The reuptake of Ca2+ then resets the tropomyosin-troponin complex

(also uses ATP), blocking the myosin binding site on actin

- A contraction will only proceed if Ca2+ is then available to bind to

troponin again and occurs via a signal from the neuromuscular junction

When does the muscle contraction end?

The endpoint of the muscle contraction is not at the powerstoke it is at the RELEASE

What is the importance of ATP?

- The "Energy" currency

- Chemical energy needed by the body is

trapped in CHO, protein and fat

- The energy is released in relatively small amounts by a controlled set of enzymatic reactions as needed

- Allows for less loss of energy from heat and greater efficiency in energy transformation

- We do not transfer energy directly from food, but in the form of ATP (we store it and break it down with the support of vitamin B12)

What is the hierarchy of ATP use?

- Free ATP and Creatine P

--Does not require oxygen

--Limited in supply ([CP] is 4 to 6x greater than ATP & CP regenerates ATP)

--Estimated to last for seconds of activity

- ATP derived from anaerobic and aerobic means (Glycolysis and glycogenolysis, TCA & Oxidative phosphorylation)

What is the significance of Creatine Phosphate (CP)?

Creatine phosphate donates a phosphate group (in the body, there are not a lot of molecules that have that ability)

- It is a power agent that is good for short-term, high-intensity exercise

What is the process like for Macronutrient fuel stores?

- In any one activity, you will get energy from multiple sources

- The body does not do anything in just one way

- We have lots of intramuscular fuel (Fat fuel in the muscle)

- Storage is limited - so then we must rely on extracellular fuel

- TCA cycle supported by carbon skeletons

- LDL and VLDL can pull TG

- Fat in blood and adipose tissue

- Muscle glycogen (focus= contraction) and liver also have lots of glycogen for blood sugar regulation

- Gatorade spares both muscle and liver glycogen

What is the fuel use during different physical activity intensities?

- As intensity increases, you lean more on the use of carbs and intramuscular fuels

- At high intensity, carbs are more important; as oxygen decreases, your systems shift to anaerobic mechanisms

What does the metabolic process make?

Electron carriers (ATP, NADH, & FADH2)

What is the difference in usage between ATP, NADH, and FADH2?

The ATP generated can be used immediately for energy, but NADH and FADH2 must be further processed to make ATP

- This further processing is done in the mitochondria of the cell

- 3 ATP per NADH; 2 ATP per FADH2

What is the fuel like from CHO?

- Comes from either blood or muscle glycogen

- Anaerobic breakdown of glucose yields 2-3 ATP molecules; glycolysis

- Aerobic breakdown of glucose yields 36 - 38 molecules of ATP; TCA cycle and electron transport chain

* Variation in the amount produced comes from what type of cycle it is using and where it comes from (Blood or muscle)

What are granules of glucose? Importance?

- These granules are storage sites in places where there is a need for lots of glycogen = glycogen-dependent systems)

- There are multiple branches where glycogen is broken down, which is quick and efficient

- There is cleavage of many glucose at a single time point

What is glycogenolysis?

process breaking down stored glycogen into glucose to supply immediate energy and maintain blood sugar levels

- once you bring glucose into the muscle cell, it is either stored or oxidized and will never again leave as glucose

- in the liver, glucose can leave again as glucose

What is glycolysis?

splits one six-carbon glucose molecule into two three-carbon pyruvate molecules inside the cytosol of a cell

-

What is the importance of lactate?

- It is a precious molecule, as it can be recycled and provide blood glucose

- Hated due to its association with fatigue

- The Cori cycle produces lactate

What is the fate of pyruvate?

- Pyruvate had multiple fates

- The TCA cycle is where all the carbon dioxide is created

- Creating acetyl-CoA (fat, proteins, & carbs meet)

- This is the intermediate that will slow things down (limiting factor = oxaloacetate)

- Electron carriers go into the TCA cycle

What is the need for Anaplerosis?

- This is the way that we use protein (amino acids) to feed the TCA cycle

- small pool that sits in the muscle (muscle as the capacity to make)

- all three macronutrients will support energy metabolism

What is the electron transport chain?

- On the inner mitochondrial membrane (there is a lot of surface area) = double membrane

- There is the movement of electrons

- Iron is an important cofactor

- Shifting hydrogen ions into the mitochondrial space creates an electrochemical gradient imbalance

- H+ ions go through ATPase, as it cannot just go through the membrane

- Maximizes ATP production

What is the summary of Glucose Oxidation?

- 1 glucose yields:

- 6 CO2

- 4 ATP (2 glycolysis (assume glucose coming from blood) & 2 TCA)

- 10 NADH (2 glycolysis, 2 PDH, 6 TCA)

- 2 FAD (TCA only)

- Each NADH = 3 ATP, FADH2 = 2 ATP

- Total = 38 ATP

What is the fuel from lipids like?

- PLENTIFUL with an estimated 90,000 to 110,000 kcal of energy

- Compared to glucose at 2000 kcal

- Sources include: Intramuscular TG, TG in lipoprotein complexes & FFA from adipose tissue

- Fats have similar transporters like GLUT 4 ( as we need to get fat into the mitochondria & muscle)

- Glycerol is important as it can be used to create glucose (glycolosis) = we recycle in the body

What is beta Oxidation?

- Fatty acids are not created equal

- cleaving 2 carbons at a time from a fatty acid (2 carbons = 5 ATP)

- 1 fatty acid ( 16 carbons) = 130 ATP

- There is lots of fuel in fats

What shifts when you start increasing intensity?

- Shift to anaerobic system as we have a limiting oxygen supply problem (Blood flow)

- Body only knows that I need to run

- Less free fatty acids in circulation - less delivery (must rely on more intramuscular TG)

The Switch from Lipids to Glucose - Why does this happen?

- Reduced blood flow to adipose tissue

- Leads to reduced availability of FFAs to muscle

- Reductions in lipid transport (Into the muscle and mitochondria)

- Reductions in intramuscular TG hydrolysi

What is the fuel from protein like?

- Protein contributes very little to energy (5-15%) (Free aa pool is small; must come from liver tissue and non- contractile proteins in the muscle)

- Muscle can perform transamination reactions

- Anapleurosis

- Glucose-alanine cycle

- if you decrease carbs, you need to increase protein to not lose FFM

What are the training Effects on Metabolism - Endurance Exercise?

- Reduction in RER or RQ (Shift downward at the same absolute workload)

- RER or RQ ( The ratio between VCO2 and VO2)

- Indicates use of fuel

0.7 = fat use

0.85 = mix of CHO and fat use

1.0 = CHO use

What are the two important training effects of metabolic endurance exercise?

- Reduced glycogenolysis (as we become much more efficient at using fat metabolism = lower amounts of muscle glycogen and plasma glucose)

- Increased fat oxidation (more intramuscular TG & good at using it)

What are the training effects on metabolism with endurance and resistance exercise?

- Increase in muscle protein synthesis (MPS) occurs after exercise

- This is dependent on volume and frequency of activity

- Too little = no increase in MPS and Too much = reductions in MPS (diet-dependent)

With training, do changes in MPS occur/ peak for trained and untrained individuals?

- Peaks at 2-3 hours for trained individuals, then quickly reverts to baseline

- Peaks at 16 hours for untrained individuals, then reverts to baseline more slowly