chapter 7 metabolic responses and adaptations to training

Copyright © 2012 American College of Sports Medicine

Chapter 7Metabolic Responses and Adaptations to Training

Chapter 7Metabolic Responses and Adaptations to Training


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


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


Adenosine Triphosphate (ATP)Adenosine Triphosphate (ATP)


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



• 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



• 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



• 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



• 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



• 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



• 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%



• Lactate

– Negative impact on performance

– Lactate production from pyruvate contributes to muscle fatigue



• 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



• 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


Krebs CycleKrebs Cycle


The Electron Transport ChainThe Electron Transport Chain



• 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



• 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



• 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



• 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



• 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


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


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



• 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



• 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



• 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


Oxygen Consumption During Exercise and Excess Postexercise Oxygen ConsumptionOxygen Consumption During Exercise and Excess Postexercise Oxygen Consumption



• 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



• 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

chapter 7 metabolic responses and adaptations to training

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