Energy Transfer in the Body

Transcription

1 Energy Metabolism Energy Transfer in the Body Refer to text for more detail. Energy the capacity or ability to perform work. Energy is required for muscle contraction and other biological work such as digestion, nerve conduction, secretion of glands, etc. Metabolism the sum total of all chemical reactions occurring in the body. Biologic Work in Humans Adenosine Triphosphate (ATP) Mechanical Work Transport Work Chemical Work Nitrogen Phosphorous Carbon Oxygen The most common immediate energy currency of the cell (the all purpose nucleotide) Metabolic Production of ATP Aerobic Processes processes which require the presence of oxygen delivered by the blood +P i Energy Adenosine Triphosphate Nitrogen Phosphorous Adenosine Diphosphate Carbon Oxygen 1

2 ATP-CP (Phosphagen) System All-out power for approximately 10 seconds Biologic Work ATP!## #" ADP + Pi + ATPase CP!## #" C + Pi + Creatine Energy Energy Kinase Principle of Coupled Reactions Anaerobic Glycolysis The Glycolytic System Glucose Glucose Net production of 2 or 3 ATP molecules 10 chemical reactions 2 Pyruvate Lactate Lactate Anaerobic Glycolysis Glucose can be made available in the muscle cells for breakdown to lactate principally by two methods: Anaerobic glycolysis can produce ATP rapidly to help meet ATP requirements during severe exercise when oxygen demand is greater than oxygen supply High rates of ATP production by glycolysis cannot be sustained for very long (40-60 sec.) Low muscle ph is associated with hydrogen ion concentration and lactate formation High acidity is believed to contributes to the acute muscular discomfort experienced during intense exercise. glucose molecules may pass from the blood through the muscle cell membrane into the cell interior (net 2 ATP), or the glucose can be split from glycogen stores in the muscle cell itself (net 3 ATP). Glycogen is stored in liver and muscle tissue. Predominates in all-out efforts seconds meters 2

3 Aerobic Processes Aerobic Carbohydrate Breakdown Pyruvic Acid Acetyl Coenzyme A Krebs Cycle Electron Transport Chain Anaerobic Conditions Glucose Pyruvate Glycolysis (2 ATP) Glycolysis (2 ATP) Pyruvate Aerobic Conditions No O 2 available Lactate O 2 available Krebs cycle Electron TC Wall of Mitochondria Total 38 ATP 36 ATP +CO 2 +H 2 O ATP Yield Do not worry about specific yields of ATP. Depending on whether glycogen or glucose is used and depending on which shuttle system is used to transport NADH molecules to the mitochondria you can get yields of 36 to 40 ATP. The main thing is to see the approximate increase in ATP yield between anaerobic breakdown (2 or 3 ATP) versus aerobic breakdown (36-40 ATP) Predominates in the majority of daily activities and lower intensity, long-duration sports. An all-out effort of 2 minutes is approximately 50% aerobic and 50% anaerobic Aerobic Breakdown of a Glycogen Molecule Glycogen Glucose Pyruvate Acetyl - CoA Kreb's cycle Electron Transport C + O 2 CO 2 + H 2 O + ATP 3

4 Energy Release From Fat The actual fuel reserves from stored fat represent approximately 80,000 to 100,000 kcal of energy in an average size male or female. In contrast, the carbohydrate energy reserve is less than 2,000 kcal, of which 1,500 kcal are stored as muscle glycogen, 400 kcal as liver glycogen, and about 80 kcal of glucose are in the blood. Aerobic Breakdown of Fatty Acids Fat Fatty acids Beta oxidation Less efficient than carbohydrate in terms of energy per O 2 used Acetyl-CoA Kreb's cycle Electron Transport C + O 2 CO 2 + H 2 O + ATP Energy Release From Protein Research findings indicate that protein breakdown above the resting level occurs during exercise of long duration when carbohydrate stores become low. It has been suggested as much as 15% of the energy during strenuous long duration exercise can come from protein. Aerobic Breakdown of Proteins Protein" Amino acids Deamination Kreb's cycle Electron Transport Chain + O 2 CO 2 + H 2 O + ATP % phosphagen anaerobic % glycolytic anaerobic % aerobic 5 seconds seconds seconds seconds minutes minutes minutes minutes Negligible minutes Negligible minutes Negligible 1 99 Relative contribution of aerobic and anaerobic energy during maximal physical activity of various durations. Duration of Maximal Exercise Seconds Minutes % anaerobic % aerobic

5 % Max Power Phosphagen Lactic Lactate Energy Production Continuum The text graph shows this on logarithmic scale Aerobic Figure 6.5 in text ATP-Creatine Phosphate System General Characteristics of the Three Energy Systems ATP!### " ADP + P + Energy ATPase CP!### " C + P + Energy Creatine Kinase For a max 1 second effort you do not really need to resynthesize much ATP you have enough in the muscle already i i Table 6.3: Estimated Maximal Power Output and Capacity of the Three Energy Systems Energy System Power Moles ATP per minute Capacity Total moles of ATP available ATP-PC (phosphagen) Glycolytic Aerobic System Aerobic Power 28% of Peak Phosphagen System Power Glycolytic System power 44% Peak Phosphagen Power (Some researchers report this value to be higher 60%) Capacity and Power of the Three Energy Systems (Untrained Male Subjects) ATP Production Energy System Capacity Power (total moles) (moles/min) Phosphagen (ATP/PC) Anaerobic gylcolysis Aerobic (oxidative) Theoretically Unlimited 1.0 5

6 Rankings of Rate and Capacity of ATP Production System ATP-PC (phosphagen) Power rate of ATP production Capacity capacity of ATP production 1 4 Anaerobic glycolysis 2 3 Oxidation of 3 2 carbohydrates Oxidation of fats and proteins 4 1 Human Power Output (energy systems) Graph from Champion Athletes Wilkie 1960 Time Motion Studies Energy Transfer in Exercise The energy systems previously discussed are related to all human activity. We now need to relate this information specifically to exercise. English 1 st Division (Premier) Players Position and Distance Covered (in meters) Activity Mid-field Full-back Striker Centre-back Average Jog Cruise Sprint Walk Back Total

7 Ajax Amsterdam Data Soccer Activity Percentage of Total Match Time Walk 20-30% Jog 30-40% Run 15-25% Sprint 10-15% (18%) Backwards 4-8% Duration Classification Predominate Energy Supplied By 1-4 seconds Anaerobic ATP (in muscles) 4-20 seconds Anaerobic (ATP-PC/Glycolytic) secs Anaerobic (Glycolytic/ATP-PC) secs Anaerobic (Glycolytic) secs Aerobic + Glycolytic ATP + PC + Some muscle glycogen ATP + PC + Muscle glycogen Muscle glycogen Muscle glycogen + a little from other fuels >240 secs Aerobic Muscle glycogen + Fatty Acids + Protein Predominant Energy Pathways 0s 4s 10s 30s 3 min + ATP ATP-CP ATP-CP + glycolytic Oxygen Strength Power Sustained Power Anaerobic Power Endurance Aerobic endurance Five Areas of the Energy Continuum Performance Time Intensity of Event 0-6 seconds Very Intense 6-30 seconds 30 seconds 2 minutes Intense Major Energy System(s) ATP-CP ATP-PC and Glycolytic Types of Activity Jumping, throwing, kicking, 50 metre sprints, base-running metre sprints Heavy Glycolytic metres run, ice hockey shifts, box lacrosse shifts, 100-metre swim 2-3 minutes Moderate Glycolytic and oxidative >3 minutes Light Oxidative systems metre runs Running > 1000 metres, distance cycling, cross country skiing, swimming > 200-m % phosphagen anaerobic % glycolytic anaerobic % aerobic 5 seconds seconds seconds seconds minutes minutes minutes minutes Negligible minutes Negligible minutes Negligible 1 99 Sports or Activity Phosphagen System Primary Metabolic Demand From Anaerobic Glycolysis Aerobic Metabolism Baseball High Low - Basketball High Moderate to High - Field Events High - - Field Hockey High Moderate Moderate Football (American) High Moderate Low Ice Hockey High Moderate Moderate Lacrosse High Moderate Moderate Marathon (42 km) Low Low High Soccer High Moderate Moderate Tennis High Moderate - Volleyball High Moderate - Wrestling High High Moderate Weight Lifting High Low Low 7

8 Average VO 2 max (ml/kg.min) for Non-Athletes and Athletes From Group Chapter or Sport 5 you Age should Male see a high Female Non-athletes positive correlation between a sport with a high demand on the oxidative system and the athletes VO max Baseball Cycling Football Gymnastics Ice Hockey Rowing Average VO 2 max (ml/kg.min) for Non-Athletes and Athletes Group or Sport Age Male Female Skiing Alpine Skiing Cross-country Soccer Speed Skating Swimming Weight Lifting Wrestling Oxygen Deficit Oxygen Debt VO 2 (l/min) O 2 Deficit O 2 Deficit Steady State O 2 consumption Rest Time VO 2 Resting VO 2 Exercise TIME O 2 Debt Recovery O 2 Deficit Oxygen Debt after Anaerobic Exercise Oxygen Debt VO 2 max O 2 Deficit Rapid portion of debt O 2 Debt O 2 Debt Slow portion of debt Exercise TIME Recovery Exercise TIME Recovery 8

9 Figure 6.11 Lactate threshold and the onset of blood lactate (OBLA) Recommended Recovery Times after Exhaustive Exercise Recommended Recovery Time Recovery Process Minimum Maximum Restoration of ATP & CP 2 min 3 min Repayment of alactate O 2 debt 3 min 5 min Restoration of O 2 -myoglobin 1 min 2 min Restoration of muscle glycogen 10 hr 46 hr (prolonged) 5 hr 24 hr (intermittent) Removal of lactate from 30 min 1 hr (exercise-rec) muscle and blood 1 hr 2 hr (rest-recover) Repayment of lactate O 2 debt 30 min 1 hr Ice Hockey Post-Game Recovery A light bike ride before/after exercise is a great way to warm-up or cool down along with stretching. Also, riding after a game helps to "flush out" lactic acid and other waste your muscles produce during activity; A cool-down flush ride should last around 10-min (often up to 30-min); Get your heart rate up around 140 bpm (Level II) for 5 min, then back off to a easy spin (Level I); You don't want to go hard enough to produce any more lactic acid (lactate); Stretch!!! This quote from Paul Goldberg, of the Colorado Avalanche, February 1 st, Lactate does not cause muscle soreness Blood Markers Despite the commonly held belief that lactic acid (lactate) causes muscle soreness this has been discredited. Delayed onset muscle soreness is likely caused by damage to muscle fibers and associated connective tissue. Getting a ball in the face also causes soreness! If we take a blood sample from a runner the day after a marathon, especially an ultra-marathon, we find that the levels of an enzyme called creatine kinase are very high. This is a marker of muscle damage as this particular enzyme "leaks" from damaged muscle. The "damage" is in the form of minute tears or ruptures of the muscle fibres. We can see this trauma to the muscle if a sample of muscle is examined microscopically. 9

10 Blood Markers (cont.) However, it is not just the muscle that is damaged. By measuring hydroxyproline, it is possible to show that the connective tissue in and around the muscles is also disrupted. What this shows is that stiffness results from muscle damage and breakdown of connective tissue. Muscle Fatigue and Lactate Lactic acid does not actually exist as an acid in the body but rather as lactate. Producing lactate is a beneficial process since it allows the regeneration of a coenzyme that ensures that energy production is maintained and exercise can continue (see text). Lactate also does not cause an increase in acidity (acidosis) within the muscle. When ATP is broken down to release energy for muscular contraction a hydrogen ion is released. This increases acidosis. Muscle Fatigue & Calcium Channels Leaked calcium also stimulates an enzyme that attacks muscle fibers and also leads to fatigue and possible damage. However, as very high acidity could also cause damage to the cells the calcium leaks may be a protective mechanism to prevent muscle cell damage due to excessive acidity. Stretching and DOMS There is no statistically strong evidence that stretching reduces post exercise muscle soreness. Intense stretching can cause muscle soreness. Muscle Fatigue and Hydrogen Ions ATP-derived hydrogen ions are primarily responsible for increases in acidity in the muscle. High acidity is one factor that contributes to acute muscular discomfort experienced during and shortly after intense exercise. However, recent evidence suggests fatigue is caused by calcium leaking into muscle cells from release channels within the muscle. Calcium helps control muscle contractions but after extended high-intensity exercise, channels in the muscle cells begin to leak calcium, which leads to weakened muscle contractions. Neural Fatigue There is also the issue of Central Nervous System (CNS) fatigue. During intense repeated bouts of strenuous exercise neurotransmitters get depleted and reduces physical and cognitive performance. Central and peripheral fatigue factors are discussed in text Chapter 6. 10