Transcript Adenosine Triphosphate (ATP) and Metabolic Systems (cont`d)

Chapter 7
Metabolic Responses and
Adaptations to Training
Copyright © 2012 American College of Sports Medicine
Introduction
• Definitions
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Metabolism: sum of all chemical reactions in the human body to
sustain life
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Exergonic reactions: result in energy release
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Endergonic reactions: result in stored or absorbed energy
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Bioenergetics: flow of energy change within human body
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Energy
• Ability to perform work
• Changes in proportion to magnitude of work performed
• Chemical energy needed for several metabolic processes
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Adenosine Triphosphate (ATP) and
Metabolic Systems
• Overview
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Body requires continuous chemical energy for life & exercise
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Potential energy transferred from storage or food to fuel muscle
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ATP
• High-energy compound used to fuel body
• Composed of adenine & ribose (adenosine) + 3 phosphates
• Hydrolysis: cleavage of phosphate bond releases energy
• ATP + H2O  ADP + Pi + energy
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Adenosine Triphosphate (ATP)
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Three Ways Energy Can Be Used Quickly
1. Skeletal muscle ATP stores
• Capacity: a few seconds of exercise
2. Phosphocreatine (PC) system
• Capacity: 5-10 seconds of high-intensity exercise
• PC stored in skeletal muscle (×4 > than ATP)
• ADP + phosphocreatine 
ATP + creatine
3. Production of ATP from multiple ADP sources
• Capacity: >10 seconds of exercise
• 2 ADP  ATP + AMP
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Phosphagen Repletion
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ATP-PC resynthesis is critical to explosive exercise performance
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High-intensity exercise depletes PC by:
• 60-80% in first 30 seconds
• 70% in first 12 seconds
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Longer-duration high-intensity exercise reduces PC by 89%
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Greater the PC degradation, the longer the time to recover PC
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Biphasic response: faster + slower components
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Factors: intensity, volume, muscle pH, ADP level, O2 availability
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Anaerobic Training Adaptations
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Positive adaptations in ATP-PC & adenylate kinase metabolic
systems
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Occur in three ways:
• Greater substrate storage at rest
• Altered enzyme activity
• Limited accumulations of fatiguing metabolites
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Glycolysis
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IS—the breakdown of CHOs to resynthesize ATP in cytoplasm
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Anaerobic metabolic system
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Capacity: 2 min of high-intensity exercise
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Rate of ATP resynthesis not as rapid as that of PC
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Larger glycogen than PC supply in body
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Gluconeogenesis: reforming of glucose in opposite direction of
glycolysis
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• Fast glycolysis is also known as anaerobic glycolysis and slow
glycolysis is commonly called aerobic glycolysis. These are
dictated by the energy demands of the cells. If there is a rapid
or high rate of type II muscle fibers being utilized then fast
glycolysis is utilized. If there is a demand for primarily type I
muscle fibers and oxygen present then slow glycolysis is
utilized.
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Control of Glycolysis
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Inhibited by:
• Sufficient oxygen levels (steady-state exercise & rest)
• Reductions in pH
• Increased ATP, PC, citrate, & free fatty acids
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Stimulated by:
• High concentrations of ADP, Pi, & ammonia
• Slight decreases in pH & AMP
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Regulated by enzyme control & negative feedback systems
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Glycogen Metabolism
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Muscle glycogen = quick source of glucose
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> glycogen availability preexercise  endurance performance
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Glycogen use:
• Most rapid at beginning of exercise
• Increases exponentially as intensity increases
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Muscle & liver glycogen repletion:
• Critical to recovery after exercise
• Factors: hormonal action, glucose uptake, blood flow,
Amount of CHOs consumed!!
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Training Adaptations
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Changes in substrate storage & enzyme activity
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Aerobic training (AT):  muscle glycogen in FT & ST fibers
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Steady-state AT & high-intensity interval training: 
muscle glycogen storage
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Sprint training: may not change or increase glycogen content
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RT: increases resting glycogen content by up to 112%
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Lactate
(p-111)
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Negative impact on performance
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Lactate production from pyruvate contributes to muscle fatigue
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Lactate is produced by your body in response to aerobic exercise
and serves as a fuel for the muscles, delays fatigue and prevents
injury. Lactic acid contains one additional proton and is not
produced by the body at all during exercise.
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The technical difference between lactate and lactic acid is
chemical. Lactate is lactic acid, missing one proton.
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• To be an acid, a substance must be able to donate a
hydrogen ion; when lactic acid donates its proton, it
becomes its conjugate base, or lactate. When you're
talking about body's lactate production and lactate or
lactic acid threshold, the difference is largely a matter of
semantics. But, the body produces and uses lactate -not lactic acid.
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Metabolic Acidosis and Buffer Capacity
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Blood & muscle pH decrease during & after anaerobic exercise
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Acidosis:
• Adversely affects energy metabolism & force production
• Causes onset of fatigue to be rapid
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Buffering capacity:
• Ability to resist changes in pH
• Increased after 7-8 weeks of sprint training
• Greater in trained than in untrained people
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• Increasing muscle buffer capacity enables greater tolerance for
acidosis. Higher lactate concentrations are seen following anaerobic
training with concomitant improvements in performance. Enhanced
buffer capacity prolongs high-intensity exercise. Trained individuals
have a greater buffer capacity than untrained individuals. Muscle
buffer capacity may increase by 16%-44% after 7-8 weeks of sprint
training. RT may lesson H+ accumulation but may not increase buffer
capacity.
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Aerobic Metabolism
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Occurs when adequate oxygen is available
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Is primary source of ATP:
• At rest
• During low to moderate steady-state exercise
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Majority of energy comes from oxidation of CHOs & fats
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Krebs cycle
(where the aerobic system begins)
• Continues oxidation of acetyl CoA
• Produces 2 ATP indirectly
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Krebs Cycle
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The Electron Transport Chain
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Energy Yield From Carbohydrates
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3 ATP produced per molecule of NADH
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2 ATP produced from FADH2
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Glucose oxidation: total of 38 or 39 ATP produced
• 2 ATP from blood glucose glycolysis OR 3 ATP from stored
glycogen glycolysis
• 2 ATP from Krebs cycle
• 12 ATP from 4 NADH produced from glycolysis & pyruvate
conversion to acetyl CoA
• 22 ATP from electron transport chain
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Energy Yield From Fats
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Fat metabolism predominates at rest & in low/moderate exercise
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Lipolysis: breakdown of fats by hormone-sensitive lipase into:
• Glycerol
• 3 free fatty acids
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Fatty acids enter circulation or are oxidized from muscle stores
via beta oxidation
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Beta oxidation: splitting of 2-carbon acyl fragments from a long
chain of fatty acids
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People with high aerobic capacity can oxidize fats at a large rate
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Aerobic Training Adaptations
  # of capillaries surrounding each muscle fiber
  Capillary density: # of capillaries relative to muscle CSA
  Nutrient & oxygen exchange during exercise
  Reliance on fat metabolism
  # of mitochondria & mitochondrial density in muscle
  Myoglobin content
  Enzyme activity
  Muscle glycogen stores at rest
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Anaerobic Training Adaptations
  # of capillaries surrounding each muscle fiber
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No change in capillary density (&  with hypertrophy)
  Mitochondrial density in muscle
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No change in myoglobin content
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No change or  enzyme activity
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Adenosine Triphosphate (ATP) and
Metabolic Systems (cont’d)
• Energy System Contribution and Athletics
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All energy systems are engaged at all times
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One may predominate based on exercise:
• Intensity
• Volume/duration
• Recovery intervals
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Training systems can be designed to target each system
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Interval Training: Work-to-Rest Ratio
• The work-to-rest ratio can target energy systems:
• 1:12 to 1:20 ratios target ATP-PC
• 1:3 to 1:5 target fast glycolysis
• 1:3 to 1:4 target fast glycolysis and aerobic oxidation
• 1:1 to 1:3 target aerobic oxidation
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Metabolic Demands and Exercise
• Indirect Calorimetry
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Measurement of O2 consumption via open-circuit spirometry
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Changes in O2 & CO2 %’s in expired air compared with normal,
inspired ambient air
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Components: flow meter, computer interface
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Measure of energy expenditure
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Respiratory quotient (RQ): measure of CO2 produced per unit
of O2
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Difference between RQ and RER
• Similar to RQ, is the respiratory exchange ratio (RER)
• Although RQ assumes that gas exchange results from nutrient
breakdown ONLY, RER reflects more accurately the role of
anaerobic exercise metabolism during exhaustive exercise. It is
calculated the same way as RQ.
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Metabolic Demands and Exercise (cont’d)
• Basal Metabolic Rate (BMR)
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Minimal level of energy needed to sustain bodily functions
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Factors affecting BMR:
• Body mass
(the larger the body size, the higher the BMR—lean body mass is
a strong component of BMR)
• Regular exercise
(enhances BMR by 8-10%—based on intensity,
volume/duration and muscle mass involvement)
• Diet-induced thermogenesis
(Increase in BMR with digestions,
absorption, and assimilation of nutrients and activation of the sympathetic
nervous system in response to meal consumption) [protein—P. 119].
• Environment
(warm or cold environments can produce higher BMRs)
• Low calorie intake lowers BMR
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• Low calorie diets have the opposite effect. Decreasing calories
can decrease RMR and lead to weight can.
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BMR vs. RMR
• RMR is the energy required to perform normal bodily
functions while the body is at rest and is somewhat
similar to BMR although it is measured under less
stringent conditions (does not require a 12-hour fast or 8
hours of sleep).
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Metabolic Demands and Exercise (cont’d)
• Estimating Resting Energy Expenditure
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Important for weight loss/gain programs
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Several population-specific equations developed
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Predictor variables: body mass or LBM, height, age
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Equations
• Harris & Benedict [1st and still commonly used]
• Mifflin-St Jeor
• Cunningham
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Metabolic Demands and Exercise (cont’d)
• Estimating Energy Expenditure During Exercise
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Average energy expenditure at rest:
• 0.20-0.35 L of O2 min-1
• 1.0-1.8 kcal min-1 (about 1.2 calories per min @ rest on average—72 per hour)
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In metabolic equivalents (METs):
• Men: 250 mL min-1
• Women: 200 mL min-1
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Exercise increases energy expenditure based on intensity,
volume, muscle mass involvement, rest intervals
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Metabolic Demands and Exercise (cont’d)
• Oxygen Consumption and Acute Training Variables
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O2 consumption
• Increases during exercise in proportion to intensity
• Increases exponentially as exercise approaches steady state
• Remains elevated during recovery after exercise
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O2 deficit
• Difference between O2 supply & demand
• Larger during anaerobic than aerobic exercise
• Smaller in aerobically trained athletes than in untrained &
strength/power athletes
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Oxygen Consumption During Exercise and
Excess Postexercise Oxygen Consumption
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Metabolic Demands and Exercise (cont’d)
• Resistance Exercise and Oxygen Consumption
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Resistance exercise increases VO2 during & after a workout
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VO2:
• Greater during large muscle-group exercises than smaller
• Varies based on lifting velocity
• Greater when exercises are performed with high intensity
• Greater when exercises are performed for high rep #
• Greater when exercises are performed with short rest
intervals
• Not affected by exercise order
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Metabolic Demands and Exercise (cont’d)
• Body Fat Reductions
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Require proper diet & exercise
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Energy expenditure must exceed energy intake for net kilocalorie
deficit
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Dietary recommendations:
• Well-balanced diet from major food groups
• High water intake (this is now disputed!!)
• 55-60% of kcal from CHOs
• 15% of kcal from protein
• <25% of kcal fats
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Body Fat Loss
• Aerobic exercise helps by increasing fat oxidation during
exercise and EPOC.
• Strength training helps by increasing LBM—an increase in LBM
stimulates metabolism (BMR) and energy expenditure
throughout the day.
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