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Chapter 7 Metabolic Responses and Adaptations to Training. Introduction. Definitions Metabolism: sum of all chemical reactions in the human body to sustain life Exergonic reactions: result in energy release Endergonic reactions: result in stored or absorbed energy - PowerPoint PPT Presentation
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Copyright © 2012 American College of Sports Medicine
Chapter 7Metabolic Responses and Adaptations to Training
Chapter 7Metabolic Responses and Adaptations to Training
Copyright © 2012 American College of Sports Medicine
IntroductionIntroduction
• Definitions– Metabolism: sum of all chemical reactions in the human body to
sustain life
– Exergonic reactions: result in energy release
– Endergonic reactions: result in stored or absorbed energy
– Bioenergetics: flow of energy change within human body
– Energy
• Ability to perform work
• Changes in proportion to magnitude of work performed
• Chemical energy needed for several metabolic processes
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic SystemsAdenosine Triphosphate (ATP) and Metabolic Systems
• Overview– Body requires continuous chemical energy for life & exercise
– Potential energy transferred from storage or food to fuel muscle
– 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
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP)Adenosine Triphosphate (ATP)
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)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
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Phosphagen Repletion
– ATP-PC resynthesis is critical to explosive exercise performance
– High-intensity exercise depletes PC by:
• 60-80% in first 30 seconds
• 70% in first 12 seconds
– Longer-duration high-intensity exercise reduces PC by 89%
– Greater the PC degradation, the longer the time to recover PC
– Biphasic response: faster + slower components
– Factors: intensity, volume, muscle pH, ADP level, O2 availability
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Anaerobic Training Adaptations
– Positive adaptations in ATP-PC & adenylate kinase metabolic systems
– Occur in three ways:
• Greater substrate storage at rest
• Altered enzyme activity
• Limited accumulations of fatiguing metabolite
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Glycolysis
– Breakdown of CHOs to resynthesize ATP in cytoplasm
– Anaerobic metabolic system
– Capacity: 2 min of high-intensity exercise
– Rate of ATP resynthesis not as rapid as that of PC
– Larger glycogen than PC supply in body
– Gluconeogenesis: reforming of glucose in opposite direction of glycolysis
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Control of Glycolysis
– Inhibited by:
• Sufficient oxygen levels (steady-state exercise & rest)
• Reductions in pH
• Increased ATP, PC, citrate, & free fatty acids
– Stimulated by:
• High concentrations of ADP, Pi, & ammonia
• Slight decreases in pH & AMP
– Regulated by enzyme control & negative feedback systems
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Glycogen Metabolism
– Muscle glycogen = quick source of glucose
– > glycogen availability preexercise endurance performance
– Glycogen use:
• Most rapid at beginning of exercise
• Increases exponentially as intensity increases
– Muscle & liver glycogen repletion:
• Critical to recovery after exercise
• Factors: hormonal action, glucose uptake, blood flow, CHOs consumed
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Training Adaptations
– Changes in substrate storage & enzyme activity
– Aerobic training (AT): muscle glycogen in FT & ST fibers
– Steady-state AT & high-intensity interval training: muscle glycogen storage
– Sprint training: may not change or increase glycogen content
– RT: increases resting glycogen content by up to 112%
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Lactate
– Negative impact on performance
– Lactate production from pyruvate contributes to muscle fatigue
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Metabolic Acidosis and Buffer Capacity
– Blood & muscle pH decrease during & after anaerobic exercise
– Acidosis:
• Adversely affects energy metabolism & force production
• Causes onset of fatigue to be rapid
– Buffering capacity:
• Ability to resist changes in pH
• Increased after 7-8 weeks of sprint training
• Greater in trained than in untrained people
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Aerobic Metabolism
– Occurs when adequate oxygen is available
– Is primary source of ATP:
• At rest
• During low to moderate steady-state exercise
– Majority of energy comes from oxidation of CHOs & fats
– Krebs cycle
• Continues oxidation of acetyl CoA
• Produces 2 ATP indirectly
Copyright © 2012 American College of Sports Medicine
Krebs CycleKrebs Cycle
Copyright © 2012 American College of Sports Medicine
The Electron Transport ChainThe Electron Transport Chain
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Energy Yield From Carbohydrates
– 3 ATP produced per molecule of NADH
– 2 ATP produced from FADH2
– 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
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Energy Yield From Fats
– Fat metabolism predominates at rest & in low/moderate exercise
– Lipolysis: breakdown of fats by hormone-sensitive lipase into:
• Glycerol
• 3 free fatty acids
– Fatty acids enter circulation or are oxidized from muscle stores via beta oxidation
– Beta oxidation: splitting of 2-carbon acyl fragments from a long chain of fatty acids
– People with high aerobic capacity can oxidize fats at a large rate
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)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
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Anaerobic Training Adaptations # of capillaries surrounding each muscle fiber
– No change in capillary density (& with hypertrophy)
Mitochondrial density in muscle
– No change in myoglobin content
– No change or enzyme activity
Copyright © 2012 American College of Sports Medicine
Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d)
• Energy System Contribution and Athletics
– All energy systems are engaged at all times
– Some predominate based on exercise:
• Intensity
• Volume/duration
• Recovery intervals
– Training systems can be designed to target each system
Copyright © 2012 American College of Sports Medicine
Metabolic Demands and ExerciseMetabolic Demands and Exercise
• Indirect Calorimetry
– Measurement of O2 consumption via open-circuit spirometry
– Changes in O2 & CO2 %’s in expired air compared with normal, inspired ambient air
– Components: flow meter, computer interface
– Measure of energy expenditure
– Respiratory quotient: measure of CO2 produced per unit of O2
Copyright © 2012 American College of Sports Medicine
Metabolic Demands and Exercise (cont’d)Metabolic Demands and Exercise (cont’d)
• Basal Metabolic Rate (BMR)
– Minimal level of energy needed to sustain bodily functions
– Factors affecting BMR:
• Body mass
• Regular exercise
• Diet-induced thermogenesis
• Environment
Copyright © 2012 American College of Sports Medicine
Metabolic Demands and Exercise (cont’d)Metabolic Demands and Exercise (cont’d)
• Estimating Resting Energy Expenditure
– Important for weight loss/gain programs
– Several population-specific equations developed
– Predictor variables: body mass or LBM, height, age
– Equations
• Harris & Benedict
• Mifflin-St Jeor
• Cunningham
Copyright © 2012 American College of Sports Medicine
Metabolic Demands and Exercise (cont’d)Metabolic Demands and Exercise (cont’d)
• Estimating Energy Expenditure During Exercise
– Average energy expenditure at rest:
• 0.20-0.35 L of O2 min-1
• 1.0-1.8 kcal min-1
– In metabolic equivalents (METs):
• Men: 250 mL min-1
• Women: 200 mL min-1
– Exercise increases energy expenditure based on intensity, volume, muscle mass involvement, rest intervals
Copyright © 2012 American College of Sports Medicine
Metabolic Demands and Exercise (cont’d)Metabolic Demands and Exercise (cont’d)
• Oxygen Consumption and Acute Training Variables
– O2 consumption
• Increases during exercise in proportion to intensity
• Increases exponentially as exercise approaches steady state
• Remains elevated during recovery after exercise
– O2 deficit
• Difference between O2 supply & demand
• Larger during anaerobic than aerobic exercise
• Smaller in aerobically trained athletes than in untrained & strength/power athletes
Copyright © 2012 American College of Sports Medicine
Oxygen Consumption During Exercise and Excess Postexercise Oxygen ConsumptionOxygen Consumption During Exercise and Excess Postexercise Oxygen Consumption
Copyright © 2012 American College of Sports Medicine
Metabolic Demands and Exercise (cont’d)Metabolic Demands and Exercise (cont’d)
• Resistance Exercise and Oxygen Consumption
– Resistance exercise increases VO2 during & after a workout
– 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
Copyright © 2012 American College of Sports Medicine
Metabolic Demands and Exercise (cont’d)Metabolic Demands and Exercise (cont’d)
• Body Fat Reductions
– Require proper diet & exercise
– Energy expenditure must exceed energy intake for net kilocalorie deficit
– Dietary recommendations:
• Well-balanced diet from major food groups
• High water intake
• 55-60% of kcal from CHOs
• 15% of kcal from protein
• <25% of kcal fats