Metabolic Pathways for Aerobic Exercise (9/25c) [Biomedical Sciences 1] Flashcards
Muscles as Metabolic Machines
Turns chemical energy → mechanical work
Catabolism of fuel → ATP breakdown → force production → movement
Muscle Fibers - Type I (slow oxidative)
Capillary density = high
Glycolytic enzymes = low concentration
Oxidative enzymes = high concentration
Mitochondrial content = high
Myoglobin content = high concentration
Muscle Fibers - Type IIa (fast oxidative, intermediate fast twitch)
Capillary density = low
Glycolytic enzymes = high concentration
Oxidative enzymes = low concentration
Mitochondrial content = low
Myoglobin content = lower concentration
Muscle Fibers - Type IIx or IIb (fast glycolytic, fast twitch)
Capillary density = lowest
Glycolytic enzymes = high concentration
Oxidative enzymes = lowest concentration
Mitochondrial content = lowest
Myoglobin content = lowest concentration
ATP overview
ATP = energy currency of the cell
ATP is broken by hydrolysis → converts to ADP, free phosphate combines with energy
ATP + H20 → ADP + Pi + Energy
[ATP] stays at about 8 mM
ATP Sinks in Resting Muscle
ATP consumption due to
- Ion pumps (Na+/K+, Ca2+, SERCA)
- RNA and protein synthesis
- fuel storage
- transport of substances
- signaling to regulate cell processes
1 mM/kh/min
ATP Sinks in Contracting Muscle
ATP consumption due to
- same ones as resting muscle
- Myosin ATPase (contraction)
240 mM/kg/min (240 fold increase compared to resting)
Chemical Pathways to Regenerate ATP
Phosphocreatine
Anaerobic Glycolysis
Oxidative Phosphorylation
Phosphocreatine
ADP + PCr + H+ ← creatine/kinase→ ATP + Cr
Spatial and temporal buffer for ATP
Critical for short term, high power activities and the transition from rest to exercise
Creatine shuttle - creatine kinase located near sites of ATP utilization and regeneration, in various points of the cell (cytoplasm)
Creatine synthesized in the liver and absorbed in the diet
Anaerobic Glycolysis
Important in transition from rest to exercise and during heavy exercise (>60% VO2max)
When oxygen is insufficient to support oxidative phosphorylation
Associated with acidosis (accumulated protons→ decline in pH)
Glucose transporter recruited by exercise and insulin
Glycolysis Pathway (in blood vessel → muscle) (cytoplasm)
- Input: glucose (5 mM), glycogen
- Output: 2-3 ATP, 2 e-/H+, pyruvate → lactate
Oxidative Phosphorylation (aerobic metabolism)
Substrate + O2 → CO2 + H2O + 5 ATP
- Substrate can be lipid, carbohydrate, or protein
Primary means of energy production
Rate is measured by oxygen consumption (VO2)
Occurs in mitochondria
- Tricarboxylic acid (TCA) cycle
- Electron transport chain
Oxygen consumption (VO2)
Proportional to workload
VO2 max represents maximal aerobic capacity
Electron transport chain (ETC)
ETC transfers electrons to O2 from H2O
Energy released used to generate ATP
Oxygen is terminal electron acceptor
Proton gradient
Tricarboxylic acid (TCA) cycle
aka Krebs or Citric Acid Cycle
strips electrons from substrate
starts with acetyl-coA and ends with 2 CO2, 1 ATP, and 4 e-
Comparison of Energy Pathways - Phosphocreatine
Time to Max Rate = immediate
Max Power = high
Max Capacity = low
O2 Required = no
Comparison of Energy Pathways - Anaerobic Glycolysis
Time to Max Rate = 5-10 sec
Max Power = moderate
Max Capacity = moderate
O2 Required = no
Comparison of Energy Pathways - Oxidative Phosphorylation
Time to Max Rate = 2-3 min
Max Power = low
Max Capacity = high
O2 Required = yes
Fuel Sources Available to Power Oxidative Phosphorylation
Lipids - huge capacity, high energy source, important at rest
Carbs/Glucose - limited capacity, moderate energy source, important during heavy exercise
Protein - moderate capacity, low energy source, important during disease and starvation
Fuel Source - Lipids
primary fuel source at rest
Slower than glucose/glycogen pathways, huge capacity (~100,000 total kcal)
130 ATP per molecule of palmitic acid
Triglyceride→ lipolysis → free fatty acids + glycerol → beta oxidation cycle and TCA cycle
Found in highest proportion in old/sedentary, or highly trained athletes
Fuel Source - Carbohydrates/Glucose
More rapid than other pathways
36 ATP per molecule of glucose
Limited capacity (~500 total kcal from muscle glycogen) - Because we store less glucose than fat
Fuel Source - Protein
Moderate capacity (24,000 kcal total)
Minor source of energy during exercise
Can be used in gluconeogenesis
Where protein enters cycle depends on what protein it is
As exercise duration increases, ___ exercise prevails over ___
aerobic over anaerobic
As duration increases, we have a greater reliance on ____
lipids
As intensity increases, we have a greater reliance on ___
carbohydrates (glycogen)
Burn more fat at ___ intensity for ___ duration
lower intensity, longer duration
How does the system adapt to training - Anaerobic
Increased aerobic substrates (ATP, PCr, creatine, glycogen)
Increased quantity and activity of key glycolytic enzymes
How does the system adapt to training - Aerobic (Metabolic)
Increased number of mitochondria
Increased oxidation of fats at rest and submaximal exercise
- Increased fat mobilizing and metabolizing enzyme
- Decreased catecholamine release during exercise
- Preserves glycogen stores to increase endurance
Increased ability to oxidize carbs at max exercise (increased glycogen content)
How does the system adapt to training - Aerobic (Cardiovascular)
Increased left ventricular volume → increase SV
Decreased HR at rest and submax exercise
Increased peripheral vasodilation capacity
How does the system adapt to training - Aerobic (Ventilatory)
Increased tidal volume and RR at submax exercise
- Increased time for oxygen diffusion into blood
- Decreased energy cost of breathing
Aerobic vs Anaerobic
Aerobic - moderate intensity, long duration activities
Anaerobic - high intensity, short duration activities
Determinants of VO2
VO2 = CO * a-VO2diff
CO = cardiac output
a-VO2 diff = (CaO2 - CvO2)
- CaO2 = arterial blood oxygen content
- CvO2 = venous blood oxygen content
- Aka oxygen extraction
Exercise - Increased cardiac output (CO)
INCREASE SV
- Positive inotropy via sympathetic stimulation
- Increased preload due to increased venous return
INCREASE HR
- Parasympathetic withdrawal (up to ~100 bpm)→ decreased activity of vagus nerve
- Sympathetic stimulation of SA node (over 100 bpm)→ direct stimulation, circulating catecholamines
Exercise - Muscle pumps increase venous return
Two muscle pumps: lower extremity (peripheral) and respiratory pumps
Works in deep venous system
Pump augments flow into the thorax during inhalation
Exercise - Redistribution of Cardiac Output
Decreased visceral blood flow
- Sympathetically mediated vasoconstriction
Increased muscle blood flow
- Locally mediated vasodilation from release of vasodilator metabolites from active muscle, vessel endothelium
Exercise - Increased Oxygen Extraction
Increased a-VO2 difference due to
- Increased oxygen consumption in active muscle
- Shunting of more blood to active muscles
Exercise - Blood Pressure
BP should increase when doing exercise
Q → increases
ΔP → increases
TPR → decreases
Dropped BP during exercise indicates
something is wrong, such as ischemia or pump dysfunction
