Chapter 3 Flashcards
Discuss the overall process of metabolism and ATP in human bioenergetics. List
the three basic energy systems used in the human body.
Bioenergetics is the flow of energy in a biological system.
These processes, known as metabolism, convert macronutrients into usable forms of biological
energy to perform work.
Metabolism includes:
• Catabolism - the breakdown of larger molecules into smaller molecules - usually
releases energy (exergonic reaction)
• Anabolism - the formation of larger molecule from smaller molecules - i.e. amino
acids to form muscle proteins - usually requires energy (endergonic reaction)
All energy used for muscle contraction is primarily derived from the hydrolysis breakdown of
adenosine triphosphate (ATP) into adenosine diphosphate (ADP) through the following
reaction:
ATP + H2O ADP + Pi + H+ + Energy
The reaction is catalyzed by the enzyme myosin ATPase.
ADP can be further hydrolyzed to adenosine monophosphate (AMP) for further energy release.
The replenishment of ATP by phosphorylation of ADP and AMP is the key process in producing
energy.
There are three basic systems used to replenish ATP in mammalian muscle cells:
1. Phosphagen system - relies on creatine phosphate to rephosphorylate ADP into ATP
2. Glycolytic system - relies on carbohydrate to rephosphorylate ADP into ATP
3. Oxidative system - uses carbohydrates and fats as sources of energy
Describe the Phosphagen System
The phosphagen system provides energy for short bursts of very intense activity.
It relies on creatine phosphate (CP) to convert ADP back to ATP.
This process occurs through a single reaction, allowing very rapid resynthesis of ATP.
This process depends on the availability of CP, and cannot be sustained for very long.
Phosphagen system
• Uses creatine phosphate to rephosphorylate ADP into ATP
• Anaerobic - does not require oxygen
• Provides ATP for short, high-intensity activities
• Relies on creatine phosphate (CP) to replenish phosphate on ADP to make ATP
➢ ADP + CP ATP + Creatine
➢ The reaction is catalyzed by creatine kinase
• Generates additional ATP from adenylate kinase reaction
➢ 2ADP ←——-> ATP + AMP
• Governed by mass-action effect - states that the concentrations of reactants on
each side will drive the direction of the reaction
• Reaction continues until exercise ceases, intensity lowers, or insufficient CP available
Describe the Glycolytic System
Glycolytic system
• Uses the breakdown of carbohydrate to resynthesize ATP
• Involves multiple reactions - slower than phosphagen system
• Higher capacity to produce ATP
• End result is pyruvate which can be converted to lactate or shuttled to mitochondria
to undergo the Kreb’s cycle
• Controlled by the concentrations of ADP, Pi, and ammonia - all signs of need for ATP
• Rate-limiting step in glycolysis is the PFK reaction - which is allosterically inhibited
by the presence of ATP
Lactate Conversion
• AKA “Fast Glycolysis”
• Allows rapid ATP resynthesis, but limited in duration due to drop in pH
• Causes metabolic acidosis through H+ accumulation - not caused by lactic acid - rise
in H+ concentration leads to fatigue
• Lactate can be oxidized in the muscle fiber or transported to the liver to be
converted to glucose through the Cori cycle
➢ Referred to as gluconeogenesis (formation of glucose from noncarbohydrate sources)
• Example of substrate-level phosphorylation
• Direct resynthesis of ATP from ADP during a single reaction in metabolic pathways
• Uses blood glucose or glycogen
• Glucose produces a net of 2 ATP molecules
• Glycogen produces a net of 3 ATP molecules
Pyruvate to Mitochondria
• “Slow Glycolysis”
• First step of aerobic system
• Shuttling pyruvate into mitochondria offers slower ATP resynthesis, but can occur
for longer
• Requires lower intensity and sufficient O2 in cell
• Nicotinamide adenine dinucleotide (NADH) also produced during glycolytic
reactions - two molecules of reduced NADH transported with pyruvate
• Pyruvate is converted to acetyl-CoA which then enters the Kreb’s cycle
• Example of oxidative phosphorylation - ATP resynthesis occurs in the electron
transport chain (ETC)
• Net reaction for glycolysis when pyruvate in mitochondria:
➢ Glucose + 2Pi + 2ADP + 2 NAD+
——-> 2Pyruvate + 2ATP + 2NADH + 2H2O
Describe the lactate threshold and the onset of blood lactate accumulation.
How can an athlete raise the exercise intensity required for OBLA?
Lactate concentration in the blood begins rising when activity reaches an intensity that passes
the lactate threshold (LT).
The LT represents increased reliance on anaerobic systems for energy demands.
Lactate Threshold (LT)
• First point of intensity where blood lactate concentration rises
• Corresponds well with ventilatory threshold
• Typically begins at 50% - 60% VO2 max in untrained individuals
• Occurs at 70% - 80% VO2 max in aerobically trained athletes
• Possibly represents increased recruitment of intermediate and large motor units
The onset of blood lactate accumulation (OBLA) is a second point of inflection in blood lactate
accumulation that occurs at higher intensities beyond the LT.
OBLA
• Second point of inflection in blood lactate accumulation
• Occurs when blood lactate reaches 4mmol/L
• Possibly represents further increased recruitment of large motor units
Training intensities near or above the LT or OBLA can increase the exercise intensity at which
athletes reach the LT or OBLA.
This adaptation allows the athlete to perform at higher intensities without as much lactate
accumulation.
Describe the oxidative system. Outline the process of oxidizing each possible
energy source.
The oxidative system is the primary source of ATP at rest and during low-intensity activities.
It can use glucose, glycogen, fats, and rarely, proteins as energy sources.
Glucose and Glycogen Oxidation
1. Begins with glycolysis
2. Pyruvate from glycolysis shuttled to mitochondria
3. Pyruvate converted to acetyl-CoA, NADH, and flavin dinucleotide (FADH2) -
4. Acetyl-CoA enters the Kreb’s cycle - produces 2 ATP from guanine triphosphate
5. NADH and FADH2 transport hydrogen atoms to the Electron Transport Chain (ETC)
6. ETC passes H atoms through a series of electron carriers, creating a proton
concentration gradient that provides energy for ATP production
7. Oxygen acts as the final electron acceptor
• Total combined ATP from one glucose including Krebs cycle and ETC = 38
• Total combined ATP from one glycogen including Krebs cycle and ETC = 39
Fat Oxidation
1. Triglycerides in fat cells broken down into free fatty acids and glycerol
2. Fatty acids enter mitochondria and undergo beta oxidation - breaks down fatty acids
into Acetyl CoA and protons (H+)
3. Acetyl CoA enters Kreb’s cycle and H+ enter ETC
4. Depending on the length of the carbon chain, one fatty acid molecule can supply
hundreds of ATP - slow process but has the greatest ATP production capacity of any
energy source
Protein Oxidation
1. Amino acids converted into glucose, pyruvate, or Kreb’s cycle intermediaries
2. Amino acid energy contribution very minimal in short-term exercise
3. Can contribute between 3% and 18% of energy during prolonged activity
4. Branched-chain amino acids most suited for oxidation in skeletal muscle
5. Urea and ammonia formed as waste products- ammonia is associated with fatigue
6. The oxidative system is inhibited by ATP presence and stimulated by ADP presence
At what exercise intensity is each energy substrate typically favored? How long
does it take to replete the substrates when depleted?
Energy substrates are selectively depleted during exercises of different intensities and
durations.
• The depletion of phosphagens and glycogen is the primary substrate depletion that
leads to fatigue
• The depletion of free fatty acids, lactate, and amino acids generally does not occur
enough to limit performance.
Phosphagen Depletion
• Creatine phosphate (CP) and ATP are rapidly depleted during intense anaerobic
exercise
➢ CP can decrease 50% - 70% during first phases of short to moderate duration
high-intensity exercise and completely depleted at the point of exhaustion
➢ ATP can decrease slightly or up to 50% - 60% during induced fatigue - ATP
concentration largely sustained by depletion of CP and production through
oxidation of other substrates
• Full resynthesis of ATP following exercise occurs within 3 to 5 minutes
• Full resynthesis of CP can occur within 8 minutes via aerobic and glycolytic systems
• Resistance training may increase total stored CP through hypertrophy of type II
fibers
At what exercise intensity is each energy substrate typically favored? How long does it take
to replete the substrates when depleted?
Glycogen Depletion
• Limited glycogen available for exercise
• 300-400g of glycogen stored in muscle
• 70-100g glycogen stored in liver
• Resting glycogen concentration can be increased through anaerobic and aerobic
training with proper nutrition
• Rate of glycogen depletion determined by exercise intensity
• Muscle glycogen used during moderate and high-intensity exercise
• Liver glycogen used during low-intensity exercise
• Repletion of muscle glycogen depends on post-exercise carbohydrate ingestion -
recommended to ingest 0.7 to 3.0g carbohydrates per kilo of bodyweight every 2
hours following exercise
• Glycogen typically replenished within 24 hours - more time needed for recovery
from intense eccentric exercise
• Blood glucose levels typically remain constant but can drop significantly during longduration exercise
Children vs Adults
• Children have higher oxidative capacity than adults
• Children show lower CP depletion and less drop in cell pH during high intensity
intermittent exercise
How do bioenergetic factors limit performance during athletic events? Discuss
the factors in short and long term event durations.
The limiting bioenergetic factors in performance vary depending on the event:
• Longer duration events are most limited by a drop in muscle and liver glycogen
• Shorter events are most limited by ATP and CP depletion
• Intense exercise of an intermediate duration (i.e. 400m run or snatch repetitions at
60% 1RM) may be most limited by drop in cellular pH
• Depletion of fat stores is not a major factor in performance but may play a role
during very-long duration events (i.e. marathon)
Describe oxygen uptake and the aerobic and anaerobic contributions to
exercise.
Oxygen uptake is the measure of a person’s ability to take in oxygen via the respiratory system,
deliver it via the cardiovascular system, and use it in muscle tissues during metabolism
• Oxygen uptake during low intensity exercise increases until the oxygen demand
equals the oxygen uptake
• Some initial energy during exercise must be supplied through anaerobic mechanisms
• The anaerobic contribution to energy during exercise is termed the oxygen deficit
• Oxygen uptake remains elevated following exercise until the body is restored to pre
exercise condition - known as the oxygen debt or excess postexercise oxygen
consumption (EPOC)
• Anaerobic mechanisms provide energy for intensities above the VO2 max - the
maximum oxygen uptake a person can sustain
What factors affect EPOC during aerobic and anaerobic exercise? What are the
factors responsible for EPOC?
EPOC varies based on the intensity, duration, and mode
EPOC During Aerobic Exercise
• Intensity has greatest effect on EPOC
• Greatest when intensity is above 50-60% VO2 max and duration above 40 minutes
• Brief bouts of exercise above VO2 max may induce greatest EPOC with lower total
work (i.e. sprints)
• Relative EPOC varies person-to-person in response to exercise
EPOC During Resistance Exercise
• EPOC depends on intensity of resistance
• Heavy resistance training (i.e. multiple sets @ 80-90% 1RM) produces greater EPOC
than circuit weight training (i.e. multiple high-rep sets @ 50%1RM)
EPOC is Caused By:
• Replenishment of oxygen in blood and muscle
• ATP/CP resynthesis
• Increased body temperature, circulation, ventilation
• Increased triglyceride-fatty acid cycling
• Increased protein turnover
• Changes in energy efficiency during recovery
How does metabolic specificity guide strength and conditioning training? List
the variables that can be manipulated during HIIT training.
The energy contributions from aerobic and anaerobic metabolism in each sport depends on the
typical duration and intensity that occurs during play
• Most sports involve some form of intense effort with interspersed rest periods
• Metabolic specificity in training refers to picking exercises and work-rest ratio that
mimic the energy demands of a sport
• Selection of the energy system used can be accomplished by manipulating the
intensity and work-rest ratio of the exercises used during strength and conditioning
Interval Training
• Emphasizes adaptations for more efficient energy transfer in metabolic pathways
• Uses predetermined work-rest ratios to allow more work at higher intensities than
continuous training
High-Intensity Interval Training
• Brief bouts of high-intensity exercise with intermittent recovery – “duty cycles”
involving high and low intensity work phases
• Efficient for eliciting cardiopulmonary, metabolic, and neuromuscular adaptations
• HIIT Variables:
➢ Intensity of active portion of duty cycle
➢ Duration of active portion of duty cycle
➢ Intensity of work during recovery portion
➢ Duration of recovery portion
➢ Number of duty cycles in each set
➢ Number of sets
➢ Recovery intensity between sets
➢ Mode of exercise
List the typical intensity, work time, and work-rest periods used to target each
energy system.
Phosphagen System • 90-100% maximum intensity • 5-10 second exercise time • 1:12 to 1:20 work-rest period Fast Glycolytic System • 75-90% maximum intensity • 15-30 second rest time • 1:3 to 1:5 work-rest period Slow Glycolytic System • 30-75% intensity • 1-3 minute exercise time • 1:3 - 1:4 work-rest period Oxidative System • 20-30% maximum intensity • 3 minute + exercise time • 1:1 to 1:3 work-rest ratio
Discuss combination training. In what context might combination training
improve performance?
Combination training is the principle of combining aerobic training into an anaerobic training
program.
Combination training was thought to improve anaerobic recovery in strength and power
athletes by improving the aerobic system, however this has generally been proven wrong.
Contraindications for Combination Training:
• Not generally effective for improving performance in well-trained anaerobic athletes
• Addition of aerobic training has been shown to decrease performance in strength
and power athletes
• On the other hand, endurance athletes may benefit from combination training.
Benefits of Combination Training:
• Combination training for aerobic athletes has been shown to improve aerobic
performance
• Additional anaerobic resistance training may be beneficial for endurance athletes
looking to improve athletic performance
