Energy Expenditure & Fatigue PDF

Energy Expenditure and Fatigue 1 Learning Objectives ¨Learn how energy expenditure is measured. ¨Examine energy expenditure at rest and during exercise. ¨Further examine the underlying causes of fatigue during exercise....

Energy Expenditure and Fatigue 1 Learning Objectives ¨Learn how energy expenditure is measured. ¨Examine energy expenditure at rest and during exercise. ¨Further examine the underlying causes of fatigue during exercise. 2 Measuring Energy Use During Exercise Direct calorimetry—measures the body's heat production to estimate energy expenditure (kcal). - Only 40% of the energy generated during metabolism of CHO and fats is used to produce ATP, the remaining 60% is used to generate heat.. Indirect calorimetry—calculates energy expenditure (kcal) from the ratio of CO2 produced and O2 consumed 3 CALORIMETRIC CHAMBER - The heat generated within the subject’s body is transferred to the air and wall of the chamber (through conduction, convection, and evaporation) - This heat produced by the subject is then measured by recording the temperature change in the air and water flowing through the chamber. - This heat change is a measure of the subject’s metabolic rate 4  Indirect Calorimetry: Measuring Respiratory Gas Exchange Indirect because heat production (energy) is not measured directly, rather energy expenditure is measured from the exchange of O2 and CO2. The amount of O2 taken up 5 by the lungs reflects the body’s use of O2 during exercise. Indirect Calorimetry: Measuring Respiratory Gas Exchange: Respiratory Exchange Ratio (RER). w RER: The ratio between CO2 released (VCO2) and oxygen consumed (VO2).. w RER = VCO2/VO2  Since O2 is required to metabolize food energy, the RER reflects the energy substrate that is being utilized (CHO, fat, protein)  The RER value at rest is approx 0.78 to 0.80  The RER value of 0.70 indicates fat utilization.  The RER value of 1.00 indicates CHO utilization  NOTE: Protein: Nitrogen is NOT oxidized (gets excreted) so we don’t calculate RER for protein (you do get energy from the keto acids after deamination, but we still don’t calculate RER for protein) 6  RER: Determining Substrate Utilization Carbohydrate C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 38 ATP During the complete oxidation of a glucose molecule, 6 molecules of O2 are consumed and 6 molecules of CO2 are produced (6 oxygen molecules are required to utilize glucose).. RER = VCO2 / VO2 = 6 CO2 / 6 O2 = 1.0 7  RER: Determining Substrate Utilization RER can go above 1.0 (but not attributed to food (energy) utilization) ------ Why? i) Hyperventilation – CO2 increases due to over-breathing but O2 does not increase ii) Lactic acid production – Lactic acid produces more CO2 because lactic acid is buffered by Na bicarbonate to maintain proper acid- base balance in the blood When an individual performs a maxVO2 test, an RER of 1.10 or greater is an indication of achieving maxVO2 8  RER: Determining Substrate Utilization Fat C16H32O2 + 23 O2 → 16 CO2 + 16 H2O + 129 ATP.. RER = VCO2 / VO2 = 16 CO2 / 23 O2 = 0.696 = 0.70 This fat (palmitic acid) requires 23 oxygen molecules to utilize it Remember: metabolizing fat is generally aerobic, less intense, moderate exercise,  the body gets a lot of O2 to the muscles and less CO2 is produced 9  RER: Determining Substrate Utilization RER can go below 0.70 if glucose is being produced from: i) protein (keto acids) ii) fats (gluconeogenesis) in the liver 10  % kcal from CHO and fats from respiratory gas volumes Once the RER value is determined from the calculated respiratory gas volumes, the value can be compared with a table to determine: - the food mixture being oxidized - the energy expenditure of exercise (kcal) Generally, the body uses CHO and fat for energy, therefore, the RER will be between 0.7 and 1.0 11 Caloric Equivalence of the Respiratory Exchange Ratio (RER) and % kcal From Carbohydrates and Fats Energy % kcal RER kcal/L O2 Carbohydrates Fats 0.70 4.686 0.0 100.0 0.71 4.690 1.1 98.9 0.75 4.74 15.6 84.4 0.80 4.80 33.4 66.6 0.85 4.86 50.7 49.3 0.90 4.92 67.5 32.5 0.95 4.99 84.0 16.0 1.00 5.05 100.0 0.0 12 12 Example Questions (using Table on previous slide) 1.) If the RER is 1.00 a) What substrate are the cells using for energy? b) Each Litre of oxygen consumed would generate how many kcal? 2.) If the RER is 0.80 c) What substrates are the muscles using? d) Each Litre of oxygen consumed would generate how many kcal? 13 Estimating Energy Requirements (kcal/day) using RER An individual consumed a typical diet of CHO, fat and protein. The next day their respiratory gases were measured (metabolic cart) in a resting state. The RER value was 0.85 kcal/L (4.86 kcal/L O2) and they consumed an average of 0.3 L of O 2 per minute. Calculate the EER (rest, no exercise) using the following equation and RER Table kcal/day = litres of O2 consumed per day x kcal used per litre14of O2 Estimating Energy Requirements (during exercise) A runner wore a portable metabolic gas analyzer to monitor their O2 consumption during a 40 minute run in order to calculate caloric expenditure. The runner’s average oxygen uptake was 0.9 L/min The runner’s RER averaged 0.95 From chart - The caloric equivalence of an RER of 0.95 is 4.99 kcal/L of O2 How many kcal did the runner expend during the 40 minute run? kcal = litres of O2 consumed x kcal used per litre of O2 15  Isotope Measurements of Energy Expenditure Doubly labeled water - 2H2 and 18O is ingested (2 isotopes (deuterium and oxygen-18), hence the term doubly labeled) - Ingest water containing the 2 isotopes - the rate at which 2H and 18O diffuses throughout the body’s water stores and leaves the body is determined by an isotope spectrometer - Isotopes require about 5 hours to distribute throughout the body, therefore used for long term exercise (eg. Calculate energy expenditure during a marathon, etc) - Measure isotopes in urine or saliva - “gold standard” to validate other energy expenditure estimates (but expensive) 16  Key Points ______________calorimetry involves using a large chamber to directly measure heat production by the body ________________calorimetry involves measuring O2 consumption and CO2 production RER at rest = __________ to __________ RER oxidation of fat = ________________ RER oxidation of carbohydrate = ____________ ____________________can be used to determine metabolic rate over long periods of time Metabolic Rate  Rate at which the body expends energy at rest (BMR/RMR) and during exercise (EMR)  BMR – Basal Metabolic Rate (physiological functions)  RMR – Resting Metabolic Rate (resting state)  EMR – Exercise Metabolic Rate (exercise) w The minimum energy required for normal daily activity is about 1,800 to 3,000 kcal/24 hr 18 Factors Affecting BMR/RMR w As fat-free mass increases, BMR _______________ w As body surface area increases, BMR ____________ w As we age, BMR gradually _______________________ w As body temperature increases, BMR _____________ w Psychological Stress ___________________ BMR w Thyroxine and epinephrine, _______________ BMR 19  Metabolic Rate During Exercise - Assessing Maximal Oxygen Uptake (max VO2) 20  Metabolic Rate During Submaximal Exercise Metabolism increases in direct proportion to the increase in exercise intensity During exercise at a constant power output (work rate) VO2 increases from its resting value to a steady-state value within 1-2 minutes at low workloads, may take up to 5 minutes at higher workloads Steady state reflects a balance between the energy required by the working muscles and ATP production via aerobic metabolism There is a linear increase in the VO2 (oxygen uptake) with increases in power output (work rate), with a faster increase once lactic acid increases 21  O2 UPTAKE vs POWER OUTPUT Steady State It takes longer to reach steady state with increasing intensity (workloads) because lactic acid levels are higher. May be due to the need to recruit more Type II muscle fibres. 22  Maximal Oxygen Uptake (VO2max) VO2max: The maximal capacity for oxygen consumption by the body during maximal exertion Single best measurement of cardio-respiratory endurance and aerobic fitness Generally expressed relative to body weight (ml · kg-1 · min-1) VO2max declines in active people after age 25-30 by approximately 1% per year VO2max increases with physical training 23  EXERCISE INTENSITY AND OXYGEN UPTAKE Max VO2 (ml/kg/min) Elite male long distance runners and cross-country skiers: 80 –84 ml/kg/min Highest recorded VO2 max Male Norwegian cross- country skier: 94 Female: Russian cross- country skier: 77 Average male (18-22yrs): 44-50 Average female (18-22): 38-42 Sedentary M or F: 20 ml/kg/min 24 Lance Armstrong: VO2max: 93, Why? Economy of Effort Both runners had the same maxVO2 (during a treadmill test) However, Runner B uses less oxygen during exercise at all intensities (running speeds) than Runner A. Why might this occur? - Better running form or style - Specificity of training - Body weight is lower This would be an advantage….Why? - decrease time in the race - Use less glycogen/glucose stores (RER would be lower) 25 Estimating Anaerobic Effort No specific test directly measures anaerobic capacity, however there are ways to estimate it:  Excess postexercise oxygen consumption (EPOC) - examining excess oxygen consumption following completion of exercise (oxygen debt) w Oxygen deficit test, Oxygen deficit is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption (eg. Wingate anaerobic test) w Estimate lactate accumulation in muscles through blood analysis; estimate lactate threshold (LT) 26 Oxygen Deficit and Excess Postexercise Oxygen consumption (EPOC) Oxygen deficit: the oxygen required for the transition from rest to exercise is greater than the oxygen consumed (using anaerobic systems) EPOC: the mismatch between O2 consumption and energy requirements 27 following exercise (oxygen debt)  Oxygen Deficit and EPOC EPOC – after exercise, the body does not immediately return to RMR (can see this when looking at RER values) Short duration – recovery is quick Long duration – recovery is slow 28 Factors Responsible for EPOC w Rebuilding depleted ATP and PCr supplies w Clearing lactate produced by anaerobic metabolism w Replenishing O2 supplies borrowed from hemoglobin and myoglobin w Removing CO2 that has accumulated in body wtissuesIncreased metabolic and respiratory rates due to increased body temperature and norepinephrine and epinephrine levels 29 Lactate Threshold  The point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity  Lactate production is exceeding lactate clearance w Usually expressed as a % of maxVO2  A high lactate threshold can indicate potential for better endurance performance  Lactate formation contributes to fatigue 30 Relationship Between Exercise Intensity and Blood Lactate Concentration Low running speeds, blood lactate [ ] remains near resting values As running speed increases, blood lactate [ ] increases rapidly The point of rapid increase is lactate threshold (LT) 31 Lactate Threshold and Endurance Performance Lactate. threshold (LT), when expressed as a percentage of VO2max, is one of the best determinants of an athlete's pace in. endurance events such as running,. cycling and rowing. Untrained people typically have LT around 50% to 60% of their VO2max Elite athletes may not reach LT until around 70% or 80% VO2max. 32 Blood Lactate [ ] at different levels of exercise expressed as a % of max VO2 for trained and untrained subjects. The ability to perform at a higher maxVO2 reflects a higher lactate threshold 33  Onset of Blood Lactate Accumulation (OBLA) The region in which blood lactate shows a systematic increase equal to or above a level of 4.0 mM is termed the point of onset of blood lactate accumulation (OBLA). This value is considered to reflect the start of the accumulation of lactic acid OBLA in the active muscle and implies the maximum exercise intensity that a person can sustain for a prolonged period of time. OBLA is considered a strong predictor of performance in aerobic exercise. 34  Calculating LT and OBLA expressed as a % MaxVO2 Max VO2 test on a Monarch cycle ergometer Female Age: 19 Body weight: 56 kg Workload (Watts)Blood Lactate (mmol/L) 0 2.3 50 3.2 75 4.9 100 6.2 125 7.4 150 19.0 175 20.1 If this data was entered into EXCEL, and a scatterplot graph with dots connected with lines was made (workload x axis, blood lactate y axis), LT and OBLA can be determined Next slide 35 Workload vs Blood Lactate Data from Slide #35 36  Calculating LT and OBLA expressed as a % MaxVO2 (cont’d) FemaleAge: 19 Body weight: 56 kg Lactate Threshold: 125 Watts = 1.8 L/min OBLA: 65 Watts = VO2 of 1.17 L/min (calculate, see below) maxVO2 = 175 Watts = 2.5 L/min Oxygen Cost of Exercise on a Cycle Ergometer Power Output Oxygen Uptake Calculating OBLA (watts) (L/min) 50 Watts = 0.9 L/min 50 0.9 1 Watt = x 75 1.2 50/0.9 = 1/x 100 1.5 50x = 0.9 x 1 Watt 125 1.8 X = 0.9/50 150 2.1 X = 0.018 175 2.5 0.018 x 65 W = 1.17 L/min 200 2.8 37 Calculating LT and OBLA expressed as a % MaxVO2 (cont’d) Female Age: 19 Body weight: 56 kg Age Correction Factor 17 1.08 18 1.07 19 1.06 20 1.05 21 1.04 22 1.03 23 1.02 24 1.01 25 1.00 26 0.99 27 0.97 38  Calculating LT and OBLA expressed a % Max VO2 (cont’d) FemaleAge: 19 Body weight: 56 kg Lactate Threshold: 125 Watts = 1.8 L/min OBLA: 65 Watts = VO2 of 1.17 L/min maxVO2 = 175 Watts = 2.5 L/min Age Correction Factor: 1.06 Calculate Max VO2, LT and OBLA in ml/kg/min ((L/min x 1000 x ACF) / body weight) Calculate the percentage of maxVO2 that LT and OBLA occurred maxVO2 where LT occurred / max VO2 x 100 Max VO2 where OBLA occurred / max VO2 x 100 39  Calculating LT and OBLA expressed a % Max VO2 (cont’d) Max VO2 2.5 L/min x 1000 = 2500 ml/min 2500 ml/min x 1.06 (ACF) = 2650 ml/min 2650 ml/min / 56 kg = 47.3 ml/kg/min 40  Calculating LT and OBLA expressed a % Max VO2 (cont’d) Max VO2 = 47.3 ml/kg/min Lactate Threshold 1.8 L/min x 1000 = 1800 ml/min 1800 x 1.06 = 1908 ml/min 1908ml/min / 56kg = 34.1 ml/kg/min LT % of MaxVO2 (34.1 / 47.3) x 100 = 72.1 % 41  Calculating LT and OBLA expressed a % Max VO2 (cont’d) Max VO2 = 47.3 ml/kg/min OBLA 1.17 L/min x 1000 = 1170 ml/min 1170 x 1.06 = 1240.2 ml/min 1240.2 / 56 = 22.1 ml/kg/min OBLA % of MaxVO2 (22.1 / 47.3) x100 = 46.8 % 42 Determining Endurance Performance Success. w High maximal oxygen uptake (VO2max) w High lactate threshold w High economy of effort  High percentage of slow-twitch muscle fibers  Other factors for success? 43  Review wExcess postexercise oxygen consumption (EPOC) is the elevation of O2 consumption above resting levels after exercise Lactate Threshold (LT) is the point at which blood lactate begins to accumulate above resting levels during exercise, where lactate production exceeds lactate clearance. 44 Fatigue and Its Causes w Phosphocreatine (PCr) depletion, ATP decreases Glycogen depletion  “hitting the wall”  Air Temperature w Accumulation of lactate and H+  Neuromuscular fatigue  Central Nervous System  Information on next slides 45 Fatigue and Its Causes: PCr/ATP PCr is used to rebuild ATP As PCr is depleted, the ability to replace ATP is hindered Therefore, ATP also diminishes Fatigue coincides with PCr depletion 46 Fatigue and Its Causes:Glycogen Depletion Depends on the duration and intensity of the exercise Is selective to the fibre type and muscle groups involved in the exercise As glycogen is depleted, the muscles rely more on FFA (slower), therefore, fatigue quickly 47 USE OF MUSCLE GLYCOGEN DURING EXERCISE (running at 70% maxVO2 on a treadmill) Not until muscle glycogen becomes quite low (around 1.5 hrs) perceived exertion starts to increase 48 Glycogen Depletion in Different Muscle Fibre Types Staining for fibre type after a 30 Staining for glycogen after a 30 km run km run Type II are lighter than Type I - Type II still have glycogen - Type I are nearly depleted of glycogen 49 Glycogen Depletion in Different Muscle Groups Muscle glycogen use in 3 different leg muscles during 2 hours of level, uphill and downhill running on a treadmill at 70% VO2 max What muscle uses the most glycogen? gastrocnemius 50 Fatigue and Its Causes: Temperature Male Cyclists, cycled at 4 different temperatures Time to exhaustion was longest at 11°C Fatigue set in earliest at 31°C (warmest) Conclusion: high muscle temperatures may impair both skeletal muscle function and glycogen metabolism 51 Fatigue and Its Causes: Accumulation of Lactate and H+ w Short duration activities depend on anaerobic glycolysis and lactic acid is converted to lactate, causing an accumulation of hydrogen (H+). w Cells buffer the H+ with bicarbonate (HCO3) to keep cell pH between 6.4 and 7.1. w However, intercellular pH lower than 6.9, slows glycolysis and ATP production.  When pH reaches 6.4, H+ levels stop any further glycolysis and result in exhaustion.  The bicarbonate does however, prevent the pH from going lower than 6.4 (which would cause cell damage)  (see next slide) 52 Changes in Muscle pH During Sprint Exercise and Recovery Re-establishing the pre-exercise muscle pH after an exhaustive sprint requires about 30 – 35 minutes of recovery Low muscle pH is the major limiter of performance and the primary cause of fatigue during maximal, all-out exercise lasting more than 20-30seconds 53  Fatigue and Its Causes: Neuromuscular Fatigue The nerve impulse is transmitted across the NMJ to activate the fiber’s membrane and cause the SR to release calcium for muscle contraction Fatigue may occur at the NMJ, preventing nerve impulse transmission May be due to: – Acetylcholine (ACh) (neurotransmitter that relays impulses) may be reduced – Cholinesterase (breaks down ACh) might become hyperactive, therefore preventing ACh to relay impulses to the muscle – Potassium might leave the intracellular space of the contracting muscle, decreasing membrane potential to half of it’s resting value (limits an action potential or muscle contraction) 54 Fatigue and Its Causes: Central Nervous System The stress of exhaustive exercise may lead to conscious (or subconscious) inhibition of the athlete’s willingness to further tolerate pain The CNS may slow the exercise pace to a tolerable limit to prevent injury (protective mechanism) Unless the athlete is highly motivated, they will stop exercising before their muscles are physiologically fatigued Athletes need to tolerate fatigue through proper training 55 Key Points Fatigue and Its Causes w Fatigue may result from a depletion of _________ or _____________, which then impairs ATP production. w The ________ generated by lactic acid causes fatigue in that it decreases muscle _________and impairs the cellular processes of energy production and muscle contraction. w Failure of ______________ transmission may cause some fatigue. w The ___________________________ system may also perceive fatigue as a protective mechanism. 56  Metabolic Adaptations to Aerobic and Anaerobic Training 57  Aerobic and Anaerobic Training Aerobic (Endurance) Training – Improves central and peripheral blood flow – Enhances the capacity of muscle fibres to generate ATP – VO2 max can be increased by 10 – 15% with 20 weeks of endurance training Anaerobic (Power) Training – Increased short-term, high-intensity endurance capacity – Increased anaerobic metabolic function – Increased tolerance for acid-base imbalances during highly intense effort 58 Changes in VO2max With 12 Months of Endurance (Aerobic) Training Max VO2 increased from 44 to 57 ml/kg/min (30% increase) Peak speed during the treadmill test increased from 13 km/h (8 mph) to 16 km/h 59 (16 mph)  Key Metabolic Adaptations to Aerobic Training Mitochondria  number and size  oxidative enzymes (oxidative capacity improves) Fuel Storage  glycogen Fuel Use  CHO use (use more fat)  lactate production Fibre Type  slow twitch (Type I) 60  Why is CHO use  in trained individuals?  RER (Respiratory Exchange Ratio) -  lipid catabolism ( HSL, LPL) -  CHO catabolism (mainly glycogen)  LT (Lactate Threshold) -  CHO catabolism ( lactate [ ]) -  “aerobic” use of CHO that is catabolized Reminder: Catabolism: large to small molecules 61   RER RER doesn’t increase as quickly in trained individuals, there is a decrease in RER at a given workload. untrained RER trained Workloa d 62  Why a decrease in RER? i)  in mitochondria (# and size) - therefore  workload per mitochondria ii)  lipid delivery to mitochondria - therefore  in beta-oxidation of FA.... more fats, RER is lower iii)  enzymes for lipid oxidation - therefore more fat metabolized, RER is lower iv)  stimulation of CHO use ( epinephrine) - therefore more fat utilization 63   Lactate Threshold In trained individuals, at a given workload, there is a ↓ in lactate [ ] untrain Concentration ed trained Lactate Workload 64  Why an increase in lactate threshold?  mitochondria – More oxidative metabolism, therefore rely less on anaerobic metabolism  lactate [ ] clearance –  less build up of lactate in the muscle  pyruvate oxidation – More pyruvate goes into oxidation and  less lactate is required (pyruvate ↔ glucose) Glycogen sparing effect – Body spares glycogen because it is getting more pyruvate  glycogen lasts longer for fuel use 65  Aerobic Training and Capillary Supply Aerobic training results in an increase in capillary supply surrounding muscle fibres (15%) More capillaries....more blood flow... allow greater exchange of O2 and CO2, heat, waste products, and nutrients supplied to the muscle (enhances maxVO2) Increases in muscle capillary # occur within the first few weeks or months of training, research is unclear on the effects of long term training. 66  Aerobic Training and Myoglobin Content Myoglobin (an ____ containing compound that stores _________in muscle), shuttles oxygen from the cell membrane to the mitochondria O2 storage in myoglobin is used during transition from rest to exercise, providing O2 to the mitochondria ___________fibres contain more myoglobin (oxidative muscle fibres) ___________training has shown to increase muscle myoglobin content by 75% - 80%. 67  Summary – Aerobic Training Aerobic training stresses ST muscle fibres more than FT fibres. The ST fibres tend to enlarge with training. The # of capillaries supplying each muscle fibre increase with aerobic training. Aerobic training increases muscle myoglobin. Oxidative enzymes are increased with aerobic training Aerobic training improves fuel utilization: – decreasing RER, – increasing lactate threshold, – increase storage of glycogen, – glycogen sparing 68  Key Metabolic Adaptations to Anaerobic Training  ATP and PC stores in muscle  activity of enzymes involved in the ATP-PC system: – myokinase (MK) – creatine phosphokinase (CPK) – ATPase – Phosphofructokinase (PFK) Strength gains due to muscle fibre hypertrophy 69 Effects of 8 weeks of training on the anaerobic potential of skeletal muscle. (see next slide) 120 ATP-PC system 100 Glycolysis 80 60 40 20 0 MK ATP ATPase CPK PC PFK 70  Effects of 8 weeks of training on the anaerobic potential of skeletal muscle. MK (myokinase) - Resynthesizes or makes ATP, increase 20% - Catalyzes the reactions in replenishing ATP from ADP ATP stores – increase 22% ATPase activity - Breaks down ATP, increase 30% CPK activity (creatine phosphokinase) - Enzyme involved in catalyzing ATP from PC – increase 36% PC (phosphocreatine or CP (creatine phosphate) – increase 40% PFK activity (phosphofructokinase) - Involved in glycolysis, increase 118% 71  Summary: Anaerobic Training Anaerobic training improves aerobic training Improvement in anaerobic performance appears to be a result of strength gains and in the functioning of anaerobic energy systems Efficiency of movement is improved. Improved buffering capacity allows the H+ that dissociates from lactic acid to be neutralized, thus delaying fatigue. 72 Practice Questions 73 1.)A runner wore a portable metabolic gas analyzer to monitor their O2 consumption during a 20-minute run in order to calculate caloric expenditure. The runner’s average oxygen uptake was 0.65 L/min. The runner’s RER averaged 0.75. The caloric equivalence of an RER of 0.75 is 4.74 kcal/L of O2 a)How many Litres of O2 were consumed during the 20 minute run? b)How many kcal did the runner expend 74 during the 20 minute run? 2.) A 22 year old male weighing 64 kg performed a VO2 max test on a bike. Their maximum oxygen uptake (VO2 max) was 2.82 L/min. Lactate threshold occurred at 2.02 L/min. OBLA occurred at 1.26 L/min. (age correction factor: 1.03) a)What was this individual’s VO2 max in ml/kg/min? b) What percentage of VO2 max did lactate threshold occur? c) What percentage of VO2 max did OBLA75 3. An individual performed a VO2 max test on a bike. Their final VO2 was 2.59 L/min and the VCO2 was 2.64 L/min. a) What was this individual’s RER? b) What substrate are they utilizing for energy at the end of the test? 76