Chapter 3: Bioenergetics of Exercise and Training Flashcards
Bioenergetics
- The flow of energy in a biological system
- Primarily concerned with converting macros into usable forms of energy (ATP)
Energy
The capacity to do work
Catabolism
- The breakdown of large molecules into smaller molecules
- Associated with the release of energy
Anabolism
- The synthesis of larger molecules from smaller molecules
- Can be accomplished using the energy released from catabolism
Exergonic Reactions
Energy-releasing reactions that are generally catabolic
Endergonic Reactions
Require energy and include anabolic processes
Metabolism
The total of all catabolic/exergonic and anabolic/endergonic reactions in a biological system
Adenosine Triphosphate (ATP)
- Composed of adenosine and three phosphates
- Potential energy in bond drives all biological work
Hydrolysis
- The breakdown of one molecules of ATP to yield energy
- Requires one molecule of water
ATPase
Enzyme that catalyzes the hydrolysis of ATP
Myosin ATPase
The enzyme that catalyses ATP hydrolysis for crossbridge cycling
Calcium ATPase
Hydrolyzes ATP when pumping calcium into the sarcoplasmic reticulum
Sodium-Potassium ATPase
Hydrolyzes ATP to maintain the sarcolemmal concentration gradient after depolarization
ATP Hydrolysis
ATP + H2O –> ADP + Pi + H+ + Energy
ADP
- Adenosine diphosphate
- Result of ATP hydrolysis
Pi
Inorganic Phosphate
AMP
- Adenosine Monophosphate
- Result of ADP hydrolysis
3 Basic Energy Systems
- Phosphagen System
- Glycolysis
- Oxidative System
Anaerobic Processes
- Does not require the presence of oxygen
- Phosphagen system
- Glycolytic systems
- Occur in the sarcoplasm of the muscle cell
Aerobic Processes
- Requires the presence of oxygen
- Krebs cycle
- Oxidative system
- Occur in the mitochondria of the muscle cell
Which macronutrient can be metabolized anaerobically?
Carbs
Phosphagen System
- Drives short-term, high-intensity activities
- Highly active at the start of activity, regardless of intensity
- Relies on hydrolysis of ATP and breakdown of creatine phosphate/phosphocreatine
Creatine Kinase
- Enzyme that catalyzes synthesis of ATP from CP/PCr and ADP
- ADP + CP ATP + Creatine
How much ATP does the body store at any given time?
80-100 g (not much)
Can ATP be completely depleted?
No, too important to cellular function
Adenylate Kinase Reaction
- AKA myokinase reaction
- 2 ADP ATP + AMP
- Used to rapidly replenish ATP
Relationship between adenylate kinase reaction and glycolysis
This reaction acts as a stimulant for glycolysis
What acts as a control for the reactions of the phosphagen system?
Law of mass action (mass action effect)
Law of Mass Action (Mass Action Effect)
- Concentration of reactants or products (or both) in solution will drive the direction of the reactions
- If there’s an enzyme involved, enzyme concentration is also a major regulatory factor
Glycolysis
- Breakdown of glucose (carbs)
- Occurs in the cytosol of the cell
What is the end result of glycolysis?
Pyruvate
Pyruvate may proceed in which directions?
- Can be converted to lactate in the sarcoplasm (fast/anaerobic)
- Can be shuttled into the mitochondria (slow/aerobic)
Why is glycolysis limited in duration when pyruvate is converted into lactate?
H+ production and the subsequent decrease in pH
How is the direction for pyruvate determined?
The energy demands of the cell
What enzyme catalyzes the formation of lactate from pyruvate?
Lactate dehydrogenase
Does lactic acid form as the result of anaerobic glycolysis?
NO
Does lactate cause fatigue?
NO
What causes fatigue?
- Proton (H+) accumulation
- H+ interferes with muscle’s excitation/contraction coupling (possibly inhibiting the binding of calcium)
Metabolic Acidosis
- Exercise-induced decrease in pH
- May be partially responsible for peripheral fatigue occurring during exercise
Cori Cycle
Process by which lactate is delivered to the liver, where it is converted into glucose
Net Reaction of Glycolysis –> Lactate
Glucose + 2Pi + 2ADP –> 2 Lactate + 2ATP + H2O
Net Reaction of Glycolysis –> Pyruvate
Glucose + 2 Pi + 2 ADP + 2 NAD+ –> 2 Pyruvate + 2 ATP + 2 NADH + 2 H2O
2 Primary Mechanisms for ATP Resynthesis
- Substrate-level phosphorylation
- Oxidative phosphorylation
Substrate-level Phosphorylation
Refers to the direct resynthesis of ATP during a single reaction
Oxidative Phosphorylation
Refers to the resynthesis of ATP in the electron transport chain
Phosphofructokinase (PFK)
- The enzyme that catalyzes the conversion of fructose-6-phosphate to fructose-1,6-biphosphate
- Rate-limiting step
Glycogenolysis
The process of breaking down muscle glycogen
Glycogen Phosphorylase
The enzyme that catalyzes the breaking down of muscle glycogen
What factors stimulate glycolysis?
- High concentration of ADP, Pi, and ammonia
- Slight decrease in pH and AMP
What factors inhibit glycolysis?
Markedly lower pH, ATP, CP, citrate, and free fatty acids
3 enzymes which are critical for regulating glycolysis
- Hexokinase
- PFK
- Pyrivate kinase
Allosteric Regulation
Occurs when the end product of a reaction or series of reactions feeds back to regulate the turnover rate of key enzymes in the metabolic pathways
Allosteric Inhibition
When an end product binds to the regulatory enzyme and decreases its turnover rate and slows product formation
Allosteric Activation
When an activator binds with the enzyme and increases its turnover rate
Hexokinase
- Catalyzes the phosphorylation of glucose to glucose-6-phosphate
- Allosterically inhibited by concentration of glucose-6-phosphate in the sarcoplasm
Lactate Threshold
- An abrupt increase above the baseline concentration of blood lactate
- Represents a significant dependence on anaerobic mechanics for energy production
- Corresponds well with the ventilatory threshold
- Often used as a marker of the anaerobic threshold
When does LT occur in untrained individuals?
At ~50-60% of VO2max
When does LT occur in aerobically trained individuals?
At ~70-80% of VO2max
Onset of Blood Lactate Accumulation (OBLA)
- An increase in the rate of lactate accumulation at higher relative exercise intensities
- 4 mmol/L
What substrates does the aerobic system use for energy?
Carbs and fats (not proteins)
Beta Oxidation
- A series of reactions in which free fatty acids are broken down
- Results in the formation of acetyl-CoA and H+
- Acetyl-CoA enters Krebs cycle and H+ is carried by NADH and FADH2 to the ETC
Contribution of protein to metabolism
- Negligible during short exercise
- 3-18% of energy demands during prolonged activity
Branched-chain Amino Acids
- The major amino acids that are oxidized in skeletal muscle
- Leucine, isoleucine, and valine
- Alanine, aspartate, and glutamate may also be used
Rate-limiting step for Kreb cycle
Conversion of isocitrate to alpha-ketoglutarate (catalyzed by isocitrate dehydrogenase)
Energy System for Activities 0-6 seconds
Intensity of Event: Extremely high
Primary Energy System Used: Phosphagen
Energy System for Activities 6-30 seconds
Intensity of Event: Very high
Primary Energy System Used: Phosphagen and fast glycolysis
Energy System for Activities 30 s to 2 min
Intensity of Event: High
Primary Energy System Used: Fast glycolysis
Energy System for Activities 2-3 min
Intensity of Event: Moderate
Primary Energy System Used: Fast glycolysis and oxidative system
Energy System for Activities >3 min
Intensity of Event: Low
Primary Energy System Used: Oxidative system
Glycogen stores in the body
- 300-400 g in muscle
- 70-100 g in the liver
Bioenergetic Limiting Factors
- ATP and CP
- Muscle glycogen
- Liver glycogen
- Fat stores
- Lower pH
ATP and CP are limiting factors for activities such as?
High intensity, short duration exercises like the 100 m run or Olympic weightlifting
Muscle glycogen is a limiting factor for activities such as?
- Marathon or triathalon
- Weightlifting
Liver glycogen is a limiting factor for activities such as?
Low intensity, long duration exercises like a marathon or triathalon
Fat stores is a limiting factor for activities such as?
Not much, the activity it has the most impact on is a marathon
Lower pH is a limiting factor for activities such as?
Longer duration, high intensity activities like a 400 m run or Olympic weightlifting
Oxygen Deficit
- The aerobic system responds slowly to exercise, so anaerobic systems fuel exercise initially
- The anaerobic contribution to the total energy cost of exercise
Oxygen Debt
- After exercise, oxygen uptake remains above preexercise levels for a time according to the length and intensity of the exercise
- AKA Recovery O2 or Excess Postexercise Oxygen Consumption (EPOC)
Interval Training
A method that emphasizes bioenergetic adaptations for a more efficient energy transfer within the metabolic pathways by using predetermined intervals of exercise and work periods
Work-to-Rest Ratios
Predetermined intervals of exercise and rest periods
High-Intensity Interval Training (HIIT)
Involves brief repeated bouts of high-intensity exercise with intermittent recovery periods
Variables of HIIT
- Intensity of the active portion of each duty cycle
- Duration of the active portion of each duty cycle
- Intensity of the recovery portion of each duty cycle
- Duration of the recovery portion of each duty cycle
- Number of duty cycles performed in each set
- Number of sets
- Recovery intensity between sets
- Mode of exercise for HIIT
Interval training profile for 90-100% of max power
- Primary System Stressed: Phosphagen
- Typical Exercise Time: 5-10 s
- Range of Work-to-Rest Period Ratios: 1:12 to 1:20
Interval training profile for 75-90% of max power
- Primary System Stressed: Fast glycolysis
- Typical Exercise Time: 15-30 s
- Range of Work-to-Rest Period Ratios: 1:3 to 1:5
Interval training profile for 30-75% of max power
- Primary System Stressed: Fast glycolysis and oxidative
- Typical Exercise Time: 1-3 min
- Range of Work-to-Rest Period Ratios: 1:3 to 1:5
Interval training profile for 20-30% of max power
- Primary System Stressed: Oxidative
- Typical Exercise Time: >3 min
- Range of Work-to-Rest Period Ratios: 1:1 to 1:3
Combination Training
- AKA cross-training
- A style of training where aerobic endurance training is added to the training of anaerobic athletes
- Thought to improve recovery, since it is thought recovery relies on aerobic mechanisms