Bioenergetics of Exercise

Question 1

When do anaerobic mechanisms provide most of the energy for work?

Answer 1

If the exercise intensity is above the maximal oxygen uptake that a person can attain. Contributions from aerobic mechanisms are primary for up to 60 seconds, after which aerobic metabolism becomes the primary energy-supplying mechanism.

Question 2

Lactate Clearance?

Answer 2

Blood lactate concentrations normally return to preexercise values within an hour after activity, light activity during the postexercise period has been shown to increase lactate clearance rates. Aerobically and anaerobically trained athletes have faster lactate clearance rates. Peak blood lactate concentrations occur 5 minutes after the cessation of exercise. Blood lactate accumulation is greater following high-intensity, intermittent exercise than following lower intensity, continuous exercise.

Question 3

Protein oxidation?

Answer 3

Protein can be broken down int its constituent amino acids and converted into glucose (gluconeogenesis), pyruvate, or various Krebs cycle intermediates to produce ATP. The contribution of amino acids is minimal during short-term exercise but may contribute 3-18% during prolonged activity.

Question 4

How long do you use creatine kinase and adenylate kinase reactions?

Answer 4

Until the exercise ceases or the intensity is low enough that is does not deplete CP stores and it allows glycolysis or the oxidative system to become the primary supplier of ATP and rephosphorylate the free creatine. At this point the sarcoplasmic concentration of ATP will remain steady or increase, which will slow down or reverse the directions of the creatine kinase and adenylate kinase reactions.

Question 5

Gluconeogenesis?

Answer 5

The formation of glucose from noncarbohydrate sources.

Question 6

What are the basic energy systems in muscle cells to replenish ATP?

Answer 6

Phosphagen, glycolysis, and oxidative

Question 7

Replenish ATP after phosphagen rapidly?

Answer 7

Another important single-enzyme reaction that can rapidly replenish ATP is the adenylate kinase reaction that takes 2 ADP molecules and makes ATP plus AMP.

Question 8

Oxygen deficit?

Answer 8

At the start of an exercise bout some of the energy must be supplied through anaerobic mechanisms because the aerobic system responds slowly to the initial increase in the demand for energy. This anaerobic contribution is termed oxygen deficit.

Question 9

What type of exercise has the greatest effect on EPOC?

Answer 9

Intensity has the greatest effect and when exercise intensity/duration are high (>50-60% VO2 max/> 40 minutes) but performing intermittent bouts of supramaximal exercise (>100% VO2 max) may induce the greatest EPOC with lower total work. Heavy resistance training (80-90% 1 RM of 3 sets, 8 exercises) produces greater EPOC than circuit weight training (4 sets, 8 exercises, 15 reps, 50% 1 RM).

Question 10

Anaerobic vs. Aerobic?

Answer 10

Anaerobic doesn’t require oxygen, aerobic does. The phosphagen and glycolytic systems are anaerobic. The Krebs cycle, electron transport, and the rest of the oxidative system are aerobic mechanisms that occur in the mitochondria of the muscle cells and require oxygen.

Question 11

Oxidative phosphorylation vs. substrate-level phosphorylation in glycolysis?

Answer 11

For oxidative, the resynthesis of ATP occurs in the electron transport chain. For substrate-level, this refers to direct resynthesis of ATP from ADP during a single reaction in the metabolic pathways.

Question 12

Fatigue during exercise is associated with what type of energy substrates?

Answer 12

Phosphagens (ATP and CP) and glycogen, not free fatty acids, lactate, and amino acids.

Question 13

Interval Training: % max power, primary system, exercise time, work to rest ratio?

Answer 13

Phosphagen: 90-100%, 5-10 sec, 1:12 to 1:20
Fast glycolysis: 75-90%, 15-30 sec, 1:3 to 1:5
Fast glycolysis & oxidative: 30-75%, 1-3 min, 1:3 to 1:4
Oxidative: 20-30%, >3 min, 1:1 to 1:3

Question 14

Endergonic reaction?

Answer 14

Require energy and include anabolic processes and the contraction of muscle

Question 15

What controls glycolysis?

Answer 15

This is stimulated to increase during intense muscle actions by high concentrations of ADP, phosphate, and ammonia and a slight decrease in pH and AMP, all of which are signs of increased ATP hydrolysis and a need for energy. Glycolysis is inhibited by markedly lower pH, ATP, CP, citrate, and free fatty acids (which are usually present at rest).

Question 16

Concentrations of CP to ATP?

Answer 16

Under normal circumstances, skeletal muscle concentrations of CP are 4-6 times higher than ATP concentrations. Therefore, the phosphagen system serves as an energy reserve for rapidly replenishing ATP.

Question 17

Phosphorylation?

Answer 17

The process of adding phosphate to another molecule.

Question 18

Muscular fatigue during exercise?

Answer 18

Muscular fatigue during exercise often correlates with high concentrations of lactate but this is not the cause of fatigue. Proton accumulation from ATP hydrolysis, not the lactate dehydrogenase reaction (this uses protons, it doesn’t release them), reduces intracellular pH, inhibits glycolytic reactions, and directly interferes with muscle’s excitation-contraction coupling.

Question 19

EPOC?

Answer 19

Excess postexercise oxygen consumption is the oxygen uptake above resting values used to restore the body to the preexercise condition.

Question 20

Repletion of phosphagens after exercise?

Answer 20

Complete resynthesis of ATP appears within 3-5 minutes and complete CP resythesis can occur within 8 minutes. This is largely accomplished as a result of aerobic metabolism but glycolysis can contribute to recovery after high intensity exercise.

Question 21

How to increase resting concentrations of phosphagens?

Answer 21

Resistance training causing hypertrophy of type II fibers, as these fibers have higher phosphagen concentration than type I fibers.

Question 22

Aerobic endurance training’s effect on anaerobic performance capabilities?

Answer 22

It can reduce anaerobic energy production capabilities and gains in muscle girth, maximum strength, and speed/power related performance.

Question 23

Glycolysis leading to the Krebs cycle?

Answer 23

If oxygen is present in sufficient quantities in the mitochondria, the end product of glycolysis, pyruvate, is not converted to lactate but is transported into the mitochondria.

Question 24

Use of muscle vs. liver glycogen during exercise?

Answer 24

Muscle glycogen is more important energy source during moderate/high-intensity exercise, liver glycogen is more important during low intensity exercise. At intensities about 60% maximum oxygen uptake, muscle glycogen is more important and the entire content of some muscle cells can be depleted. Relatively constant blood glucose concentrations are maintained at very low exercise intensities as a result of low muscle glucose uptake. As durations increase beyond 90 minutes, blood glucose concentrations fall due to liver glycogen depletion.

Question 25

Phosphagen System?

Answer 25

Provides ATP primarily for short-term, high-intensity activities and is highly active at the start of all exercise, regardless of the intensity. The energy system uses ADP (from hydrolysis of ATP) and a high energy molecule called creatine phosphate to replenish ATP. Creatine kinase is the enzyme that catalyzes the synthesis of ATP. Creatine phosphate is stored in relatively small amounts so this cannot provide energy very long.

Question 26

What’s the primary source ATP at rest?

Answer 26

Oxidative system

Question 27

Metabolic acidosis?

Answer 27

Exercise-induced decrease in pH due to the hydrolysis of ATP outside the mitochondria.

Question 28

Onset of blood lactate accumulation?

Answer 28

A second increase in the rate of lactate accumulation at higher relative intensities.

Question 29

How to improve LT and OBLA?

Answer 29

Train at intensities at or above LT or OBLA and this pushes these to the right. This allows the athlete to perform at higher percentages of maximal oxygen uptake without as much lactate accumulation in the blood.

Question 30

How to optimize HIIT?

Answer 30

The active portions should equate to several minutes above 90% of VO2 max

Question 31

Creatine phosphate concentrations in different muscle fibers?

Answer 31

Type II muscle fibers have higher concentrations of CP than type I.

Question 32

Hydrolysis?

Answer 32

The breakdown of one molecule of ATP to yield energy and requires one molecule of water. It is catalyzed by ATPase, specifically myosin ATPase for crossbridge recycling, calcium ATPase for pumping calcium into the sarcoplasmic reticulum, and sodium-potassium ATPase for maintaining sarcolemmal concentration gradients after depolarization. It produces ADP, phosphate, hydrogen, and energy.

Question 33

Oxygen debt?

Answer 33

After exercise, oxygen uptake remains above preexercise levels for a period of time that varies according to the intensity/length of exercise. This postexercise oxygen uptake has been termed oxygen debt.

Question 34

Interval training?

Answer 34

Uses work to rest intervals to allow more work to be accomplished at higher exercise intensities with the same or less fatigue than if doing this continuously.

Question 35

Depletion of phosphagens?

Answer 35

Creatine phosphate can decrease markedly (50-70%) during high intensity exercise of short and moderate duration (5-30 sec) and can be almost completely depleted as a result of very intense exercise to exhaustion. Muscle ATP concentrations may decrease only slightly or up to 50-60% of preexercise during fatigue but for the most part intramuscular ATP concentration is largely sustained during exercise as a consequence of CP depletion and the contribution of additional ATP from the adenylate (myokinase) reaction and oxidation of other energy sources such as glycogen and free fatty acids.

Question 36

ATP Stores?

Answer 36

The body stores approximately 80-100 grams of ATP at any given time. ATP stores may decrease by up to 50-60% of the pre-exercise levels during muscle fatigue.

Question 37

How long to replenish muscle glycogen?

Answer 37

Can be replenished completely within 24 hours if sufficient carbohydrates are ingested.

Question 38

Lactate threshold?

Answer 38

The exercise intensity at which blood lactate begins an abrupt increase above baseline concentration. It represents a significantly increased reliance on anaerobic mechanisms and is often used as a marker for anaerobic threshold. This begins at 50-60% of maximal oxygen uptake in untrained individuals and at 70-80% in aerobically trained individuals.

Question 39

How much glycogen is stored in the body?

Answer 39

300-400 g in the body’s total muscle and 70-100 in the liver. Anaerobic and aerobic training can increase this, as well as nutrition.

Question 40

Lactate concentrations?

Answer 40

Normally it is low in blood and muscle but increases with exercise intensity and depends on muscle fiber type. There is a higher rate of production by type II fibers and represents a higher activity of glycolytic enzymes than in type I muscle fibers. Exercise duration, state of training, and initial glycogen levels can also influence lactate accumulation.

Question 41

Very high-intensity, intermittent exercise and glycogen depletion?

Answer 41

Can cause substantial depletion of muscle glycogen and be a limiting factor for resistance training with many total sets, although, phosphagens may be the primary limiting factor with high resistance and few repetitions or few sets.

Question 42

Macronutrients contributing to energy at rest and when starting intense exercise?

Answer 42

At rest 70% of ATP produced is from fats and 30% from carbs. When starting higher intensity exercise there is a shift from fats to carbs. During high intensity aerobic exercise almost 100% of energy is from carbs.

Question 43

Exergonic reaction?

Answer 43

Energy releasing reactions, usually catabolic.

Question 44

What stimulates glycolysis?

Answer 44

A powerful stimulant of glycolysis is AMP production.

Question 45

Primary energy system used based on duration and intensity?

Answer 45

Phosphagen is 0-6 seconds at extremely high intensity; phosphagen & fast glycolysis used for 6-30 seconds at very high intensity; fast glycolysis from 30-120 sec at high intensity; fast glycolysis and oxidative system from 2-3 minutes at moderate intensity; oxidative system > 3 min at low intensity.

Question 46

Benefits of HIIT?

Answer 46

Elicits a very high percentage of VO2 max as a result of recruitment of large motor units and near maximal cardiac output. Also increases VO2 max, proton buffering, glycogen content, anaerobic thresholds, and time to exhaustion.

Question 47

Fat oxidation?

Answer 47

Triglycerides stored in fat cells can be broken down to produce free fatty acids and glycerol. This releases fat cells into the blood where they can circulate and enter muscle fibers and undergo oxidation. Limited triglycerides are stored in the muscle to produce an intra-muscular source of free fatty acids. Free fatty acids enter the mitochondria and are broken down. A single triglyceride can be metabolized to produce over 300 ATP molecules.

Question 48

Glycolysis?

Answer 48

The breakdown of carbohydrate, either glycogen stored in the muscle or glucose in the blood, to resynthesize ATP. It involves multiple reactions and is not as rapid as the single-step phosphagen system but the capacity to produce ATP is much higher. This reaction occurs in the sarcoplasm and the end result is pyruvate. Pyruvate can either be converted to lactate in the sarcoplasm or shuttled to the mitochondria.

Question 49

Oxygen uptake during low intensity exercise?

Answer 49

During low-intensity exercise with a constant power output, oxygen uptake increases for the first few minutes until a steady state of uptake (oxygen demand equals oxygen consumption) is reached.

Question 50

What determines which energy system is used?

Answer 50

All 3 energy systems are active at any given time, how much each system contributes at any given time is primarily dependent on the intensity of the activity and secondarily on the duration.

Question 51

Metabolism of macronutrients and oxygen?

Answer 51

Only carbohydrates can be metabolized for energy without the direct involvement of oxygen.

Question 52

Pyruvate to lactate?

Answer 52

This is catalyzed by the enzyme lactate dehydrogenase and the end result is lactate, not lactic acid.

Question 53

Catabolism?

Answer 53

The breakdown of large molecules into smaller molecules, associated with the release of energy.

Question 54

Fast vs. Slow Glycolysis?

Answer 54

When pyruvate is converted to lactate, ATP resynthesis occurs at a faster rate but is limited in duration due to hydrogen production and decreased pH. This is termed fast glycolysis or anaerobic glycolysis. When pyruvate is shuttled to the mitochondria to undergo the Krebs cycle, the ATP resynthesis rate is lower but can occur for a longer duration if exercise intensity is low enough. This is referred to as aerobic glycolysis or slow glycolysis. The fate of pyruvate is controlled by the energy demand. If energy demand is high and must be transferred quickly then pyruvate is primarily converted to lactate. If demand is not high and oxygen is present in adequate quantities in the cell, pyruvate can be further oxidized in the mitochondria.

Question 55

Protein and energy?

Answer 55

Protein does no provide a significant contribution to total energy but does increase during long-term starvation and long bouts of exercise.

Question 56

What happens to lactate?

Answer 56

It can be cleared by oxidation within the muscle fiber where it was produced, transported in the blood to other muscle fibers to be oxidized, or transported in the blood to the liver to be converted to glucose.

Question 57

Oxidative system?

Answer 57

The primary source of ATP at rest and during low-intensity exercise and uses primarily carbohydrate and fats as substrates.

Question 58

Anabolism?

Answer 58

The synthesis of larger molecules from smaller molecules and can be accomplished used energy released from catabolic reactions.

Question 59

How much ATP is produced with the oxidation of glucose?

Answer 59

The oxidative system begins with glycolysis and includes the Krebs cycle and ETC. If oxidation starts with 1 molecule of blood glucose then 38 ATP produced, if initiation of glycolysis is muscle glycogen then 39 ATP is produced.

Question 60

Energy yield from glycolysis?

Answer 60

When glycolysis begins with 1 molecule of blood glucose, 2 ATP molecules are used and 4 are resynthesized, leading to a net of 2 ATP molecules. When glycolysis begins with glycogen, only one ATP is used and 4 are resynthesized, yielding 3 ATP.

Question 61

Metabolism

Answer 61

The total of all catabolic or exergonic and anabolic or endergonic reactions in the biological system

Question 62

Cori cycle?

Answer 62

When lactate is transported through the blood to the liver to convert it to glucose.