Energy Systems and ATP

• Lecture focuses on energy systems, dietary assessment, and Adenosine Triphosphate (ATP)
• A key learning outcome is understanding how dietary intake is converted to ATP for muscle movement.
• Energy needs, requirements, and dietary assessment tools are examined

Adenosine Triphosphate (ATP)

• ATP is the primary energy carrier in the body
• ATP is a high-energy molecule for storing and transferring energy in cells
• ATP is required for every muscle contraction, nerve impulse, and metabolic reaction
• ATP molecules have three phosphate groups
• Stored energy is contained in the high-energy bonds between phosphate groups
• ATP releases energy when hydrolysed, which breaks it down using water and ATPase enzyme
• In hydrolysis, the high-energy bond between the phosphate groups break, releasing one phosphate group
• During hydrolysis ATP is converted to Adenosine Diphosphate or ADP

Adenosine Diphosphate (ADP)

• ADP molecules have two phosphate groups
• ADP is the low-energy version of ATP
• ADP is recharged into ATP using energy from food
• ATP and ADP are always in the body
• ATP and ADP are constantly cycling between each other continuously broken down and rebuilt in every cell
• Basal Metabolic Rate (BMR) is linked to this cycle

Energy Systems

• There are three energy systems used to recharge ADP into ATP
• Systems include Anaerobic Alactic, Anaerobic Lactic, and Oxidative System
• Anaerobic Alactic System is also known as the Phosphagen System or ATP-PCr
• Anaerobic Lactic System is also known as Glycolytic System or Anaerobic Glycolysis
• Oxidative System is also known as Aerobic Metabolism

Anaerobic Alactic System or ATP-PCr

• The fastest way to provide energy, but is limited
• Immediate, explosive energy is supplied, useful for short bursts of high intensity activity (0 to 15 seconds) such as jumping, sprinting, and heavy lifting
• Phosphocreatine (PCr) donates a phosphate group to ADP to form ATP, thus no oxygen is needed
• One molecule of ATP is produced per molecule of PCr
• After ATP is used, ADP is formed
• PCr donates its phosphate to ADP to form ATP via the creatine kinase enzyme

Anaerobic Lactic System, known as Glycolytic System or Anaerobic Glycolysis

• The second fastest way to provide energy
• It supports moderate-duration, high-intensity activities that last up to 2 or 3 minutes
• Relies on the breakdown of glucose in blood or glycogen in muscles or liver to produce lactic acid as a byproduct
• No oxygen needed
• Glycolysis is the breakdown of glucose or glycogen to produce ATP
• Glycolysis can occur with oxygen (aerobic glycolysis [slow]) or without oxygen (anaerobic glycolysis [fast])
• Anaerobic glycolysis, which does not use oxygen, occurs in the cytoplasm of the cell
• Glucose is broken down into two molecules of pyruvate
• Two ATP are produced from glucose and three ATP come from glycogen
• Requires 12 enzymatic reactions to breakdown glycogen into ATP
• When there is no oxygen, pyruvic acid/pyruvate becomes lactic acid

Oxidative System or Aerobic Metabolism

• Produces the most ATP at 85%
• To create ATP, it uses glucose, glycogen, fats (triglycerides and fatty acids), and proteins (amino acids)
• Occurs in the mitochondria
• Oxygen needed
• Because it is a slow process, it is suited for endurance events, low-to-moderate intensity exercise, and long-duration activities

Oxidative System - Carbohydrates

• The system follows the same steps from the last system and yields 2 ATP, except:
• Pyruvate is not converted to lactic acid
• Pyruvate gets converted to Acetyl-Coa inside the mitochondria through aerobic glycolysis
• Acetyl-Coa enters the Krebs cycle
• The Krebs cycle, also known as the TCA or citric acid cycle, generates two ATP and electrons
• Electrons enter the electron transport chain to produce 32 to 34 ATP
• Thus, total energy produced is 2 ATP in glycolysis, 2 ATP in the Krebs cycle, and 32 or 33 ATP in the electron transport chain
• In total, 36-37 ATP are produced per glucose molecule

Oxidative System - Fats

• Fats take longer to metabolize compared to carbohydrates
• Fats are stored as triglycerides
• Lipolysis is the breakdown of triglycerides into glycerol and three free fatty acids (FFAs)
• It is the most energy dense pathway. One fatty acid produces 144 ATP.
• Glycerol gets converted to pyruvate and enters glycolysis
• Free fatty acids (FFAs) are converted to Acetyl CoA to the Krebs cycle, then the ETC (similar to carbohydrates)

Oxidative System - Protein

• Protein is the last resort and not a primary source of energy
• It is a complex process
• Some amino acids that form proteins can be converted into glucose through gluconeogenesis, including branch chain amino acids (BCAA’s)
• The nitrogen in amino acids, which cannot be oxidized, makes it difficult to determine the energy yield of protein
• Some amino acids are converted to pyruvate
• Some are converted to Acetyl CoA
• Some directly enter the Krebs cycle
• Some are converted to glucose

Energy, Intensity, Duration and Recovery

• Aerobic system converts glucose to fat for longer than 2-3 minutes

• Aerobic uses oxygen while combining Glycolysis (slow/only glucose), Krebs Cycle (FFA & AA enter), and Electron Transport Chain

• When 100% VO2max is used, the Intensity is at in the ATP-PCr and the duration is shorter than 10 seconds

• When over 85% VO2max is used the intensity is in the Anaerobic Lactic system and duration is 10 seconds to 2 minutes

• When Intensity is lower than 85% VO2max the intensity is in the Aerobic system and duration is longer than 2 minutes

• Powerlifting is an example of usage of ATP-PCr

• Four-hundred meter sprints use the Anaerobic Lactic system

• Marathon running uses Aerobic system for a long duration

• When using ATP-PCr recovery takes 3-8 min

• When using Anaerobic Lactic recovery takes less than 2 hours

• When using Aerobic system the recovery takes 2 min + All day

• ATP-PCr uses PCr, Anaerobic Lactic uses glucose, and Aerobic uses Glucose, Amino acids, fatty acids, and lactic acid as fuel

• Waste byproducts include Cr in ATP-PCr, Lactic Acid in Anaerobic Lactic system, and C02 + H20 in Aerobic system

Energy Systems Contributions

• When the body requires energy for rest or exercise, all three energy systems are used
• Energy system relative rate of usage is based on exercise intensity (primarily), and duration (secondarily)

Energy Requirements for Exercise

• Enough energy to fuel the body, support growth or development, and maintain weight
• Ein = Eout (E expenditure) so energy from food (E) = BMR + Thermic effect of food + Physical Activity

Measurement of Energy Expenditure

• Direct calorimetry measures the body's heat production to calculate energy expenditure (accurate within 1-2% in a Calorimetric Chamber)
• Indirect calorimetry calculates energy expenditure from the respiratory exchange ratio (RER) of CO2 and O2

Respiratory Exchange Ratio (RER)

• The ratio between CO2 released (VCO2) and oxygen consumed (VO2), i.e. RER = VCO2/VO2
• Ratio determines what fuels are being oxidized and calculates the energy expended per liter of O2 consumed.
• At 100% fat, RER is 0.7 while at 100% CHO, RER is 1.0
• With ketones, RER is less than 0.7 and while resting is usually 0.78 to 0.80
• Other measures include Activity diaries, Measurement of heart rate, and Doubly-Labelled water measures
• Factorial Methods include RMR x physical activity level (PAL)

Energy Expenditure Calculation

• Methods were developed by Harris-Benedict, Owen, Mifflin, Cunningham, WHO, and Schofield

Energy Costs Influences

• Factors influencing energy costs include type of activity, age, gender, intensity and duration of activity, body weight and composition, efficiency of movement, plus stress and body temperature
• The energy expenditure for large athletes engaged in intense daily training can exceed 10,000 Cal per day

Dietary Assessment

• Methods of Assessment:
• Anthropometric
• Biochemical
• Clinical
• Dietary

Dietary

• Dietary Assessment measures nutrient intake which is an indirect measure of nutritional status
• Dietary intake measures should coincide with other measures of nutritional status
• These assess and monitor food and nutrient intakes of populations and individuals
• They establish and evaluate government policy, plus are used for conducting research and commercial purposes

Dietary Assessment Techniques

• Retrospective techniques include 24 hour recall, FFQ and Diet history
• Prospective techniques include 3 day food record, 7 day food record, and Duplicate food collections

Retrospective Techniques

• Twenty-four-hour diet recall food is consumed over last 24 hours or typical day
• Pros: Quick and easy to administer, inexpensive, low participant burden, objective compared with history, good response rate, no alteration in usual intake
• Cons: May not represent usual intake, relies on memory, honesty, food knowledge, over or under reporting common, dDay chosen may be atypical

Retrospective - Diet History

• The diet history is comprised of an open-ended interview, 24-hour recall, and food frequency
• Pros: Usual intake and notes seasonal daily and variation, covers all nutrients, can match with biochemical results and Food models assist estimation of food serves
• Cons: Lengthy interview, high level of training for interviewers and high level of cooperation of cooperation (labour / time intensive)

Retrospective - Food Frequency Questionnaire

• Measures the frequency of intake of various foods or fluids
• Pros: Low participant burden, inexpensive, can be machine readable, good response rate and can cross-check data from other methods
• Cons: May not adequately represent serving sizes, suffers from memory bias and can Underestimate energy intake

Prospective - Diet Record

• Daily diet records are taken
• Pros: Fairly accurate, inexpensive, obtains detailed information, and provide information about eating habits
• Cons: May not represent normal diet, and can underestimate energy, causes compliance and attention to detail issues
• Estimates can be compared to weighing (one cup versus 200g)
• Weighed methods can increase the data accuracy but increase compliance and are more burdensome
• A seven day record is burdensome but more accurate

Dietary Information Interpretation

• Includes nutrient analysis by computer program, and food tables
• Food pattern analysis include Variety, minimum food group levels, fat content including fatty foods and fried foods and sugar content including sweetened beverages and sweets. Should compare with RDI.