Human Energy Lecture Notes PDF

Measures of energy What is energy ?  Energy represents the capacity to do work.  Different forms :  Mechanical or kinetic (eg: work).  Nuclear (eg: uranium).  Light (eg: sun).  Electrical (eg: lightning storms).  Heat (eg: fires).  Chemical (eg: oils)  These types of E ar...

Measures of energy What is energy ?  Energy represents the capacity to do work.  Different forms :  Mechanical or kinetic (eg: work).  Nuclear (eg: uranium).  Light (eg: sun).  Electrical (eg: lightning storms).  Heat (eg: fires).  Chemical (eg: oils)  These types of E are interchangeable.  In human body, chemical, mechanical, electrical and heat energy are important. How de we measure work, physical activity and energy expenditure ?  Work = force * distance.  Power = work / time (how fast work is done).  Two major measurement systems have been used to express E in terms of either work or power (english and metric systems).  Now, the international unit system (SI) is used in most scientific journals today. Unit SI Mass Kg Distance m Time Sec Force N Power Watt Work joule Some conversions 1 kg 2.2 pounds 454 grams 1 pound 1 pound 16 oz 1 meter 3.28 feet 1 km 0.62 mile  How de we measure work, physical activity and energy expenditure ?  An ergometer is designed to provide accurate measurements of work, including measures of power and total work output over specific periods of time.  Several methods are available to measure E expenditure in humans: I. Calorimetry (direct calorimetry): I. Measures heat energy. II. Large, expensive , whole-room calorimeters are available that can accommodate human beings and measure their heat production under normal home activities and some exercises. Direct calorimetry  How de we measure work, physical activity and energy expenditure ? II. Indirect calorimetry: I. Determines the amount of O2 an individual consumes (in L or ml). II. When O2 combines with a gram of CHO, fat or protein, a certain amount of E is released. III. Doubly labeled water (DLW): I. Ingestion of stable isotopes of H and O2 in water. II. Elimination of O2 as water and carbon dioxide. III. Elimination of H as water. IV. Measure of CO2 fluctuation may be converted to E expenditure. V. Doesn’t estimate exercise intensity. What is the most commonly used measure of E?  Most common term : calorie.  Calorie: measure of heat. 1 g Cal represents the amount of heat needed to raise the T of one g of water one degree celsius.  In human nutrition, we use Kcal ( = 1000 of cal) = C = Kc.  « kilojoule » is the proper term in the SI.  1 C = 4.2 Kj  1 C = 200 ml oxygen.  Because human body is not as efficient as the calorimeter (less absorption) ➔ 1 g CHO = 4 Cal. 1 g fat = 9 Cal. 1 g prot = 4 Cal. 1 g alcohol = 7 C. Human energy systems How is E stored in the body ?  Foods possess stored E. When we consume these foods, digestive processes break them down into simple compounds absorbed into the body.  E in the body is available for immediate use in the form of adenosine triphosphate (ATP) (for rapid E release).  It’s a high energy compound stored in the tissues in small amounts.  When split by enzyme action, high-E bonds can release E.  Immediate source of E for all body functions.  The other E stores are used to replenish ATP at varying rates.  Muscle contraction is totally dependant on ATP. How is E stored in the body ?  Another high E phosphate compound, « phosphocreatine « (PCr).  Not an immediate source of E but can rapidly replenish ATP.  Body stores of CHO, fat and protein can provide ample amounts of ATP, enough to last for many weeks even on a starvation diet.  Parts of each E nutrient (CHO, fat, prot) may be converted to the other two nutrients in the body under certain circumstances (prot → CHO in prolonged ex; excess CHO → fat during rest).  Stores: limited amount of CHO (BG, liver & muscle gly); major stores are of fat (+++ muscle & adipose tissue TG); protein stores are not used as an E source under normal circumstances. What are the human E systems ? I. ATP-PCr system ( = phosphagen system): I. ATP is an immediate source of E for almost all body processes. II. Limited supply ➔ must be replaced rapidly. III. PCr help regenerate ATP from ADP and P. IV. Any all-out exercise for 5-10 sec could deplete the supply. V. PCr is also in short supply and needs to be replenished if used. VI. Increasing level of PCr in muscles would enhance the performance of brief high-intensity exercise (e.g: creatine supplementation). VII. Anaerobic power is a term often associated with ATP-PCr E system. What are the human E systems ? II. Lactic acid system: I. Not a direct source of E for muscle contraction, but can help replace ATP rapidly when necessary. II. Glu → ATP (by glycolysis) ( dependant on the capacity of the mitochondria that need O2 to do this reaction). I. Aerobic glycolysis: when mitochondria can process the available glucose (= adequate O2 is available). II. Anaerobic glycolysis (= lactic acid system): when rate of glycolysis surpasses the capacity of mitochondrial oxidation, then insufficient ATP is formed and lactic acid is a by-product of the process necessary to increase ATP production (limited capacity). III. Lactic acid formation is associated with the onset of fatigue. III. The lactate present after loss of the H ion still has E content, which may be used by other tissues for E or converted back in the liver. IV. Used when E production is near maximal for 30-120 sec (200-800 m run) (anaerobic capacity). What are the human E systems ? III. Oxygen system (= aerobic/oxidative system): I. Cannot be used directly as a source of E for muscle contraction, but it does produce ATP in rather large quantities from other E sources in the body (muscle gly, liver gly, BG, muscle TG, blood FFA & TG, adipose cell TG, body protein). II. These processes occur through the krebs cycle and the electron transfer system (mitochondria). III. Lower rate of ATP production, but larger production of E in the form of ATP in the presence of an adequate oxygen level. IV. Can handle mild and moderate levels of exercise not the very strenuous ones. Subdivided into 2 systems: I. Aerobic glycolysis (high-intensity eg: 5-10 km up to 2 h) (= aerobic power). II. Aerobic lipolysis ( lower levels of ex intensity eg: 50-100 km) (= aerobic capacity). What are the human E systems ? N.B: Human E systems may be classified as anaerobic or aerobic and each subdivided into E systems for power and capacity: Anaerobic power: ATP-PCr E system. Anaerobic capacity: lactic acid E system. Aerobic power: aerobic glycolysis. Aerobic capacity: aerobic lipolysis. What nutrients are necessary for operation in the human E systems ? Water, vitamins and minerals function very closely with protein in the structure and function of many enzymes. Water: help in hydrolysis. Vitamins: needed for E to be released from the cell sources. Minerals: essential for cellular E processes.  What is metabolism ? MB represents the sum total of all physical and chemical changes that take place within the body. Two fundamental processes: Anabolism: building-up process that needs E. Catabolism: tearing-down process that creates E to support anabolism. Metabolic rate reflects how rapidly the body is using its E stores. Total daily E expenditure (TDEE) may be accounted for by 3 factors: Basal E expenditure (largest component). Increases due to eating a meal. Physical activity (most variable component). What factors account for the amount of E expended during rest ? Constant use of E to build up and tear down substances within the cells. Certain automatic body functions also consume E. Basal metabolism = BMR = E requirements of the many different cellular and tissue processes that are necessary to continuing physiological activities in a resting, post absorptive state throughout most of the day. Basal E expenditure (BEE)= BMR extrapolated over a 24-hour period. Resting metabolic rate (RMR) = BMR + small amounts of additional energy expenditure associated with eating and previous muscular activity (called also REE). What effect does eating a meal have on the metabolic rate ? It’s the dietary induced thermogenesis (DIT) or thermic effect of food (TEF) ( 1 → 4 h after a meal). It’s the energy necessary to absorb, transport, store and metabolize the food consumed. Increases with the caloric content of the meal. The type of food ingested may affect the magnitude of TEF (prot > CHO> fat). In a mixed meal, the increase in TEF is about 5-10%. Alcohol intake also causes about 15% rise in REE. Genetic & environmental factors affecting REE Genetic factors: Changes in the proportion of muscle tissue and fat cause changes in REE. Genetic factors affecting REE: age, sex, natural hormonal activity, body size and surface, body composition to a certain extent. REE declines through age. REE of women: 10-15% lower than men. Genetically lean individuals have a higher REE than stocky individuals. Losing BW lowers the daily REE (may be due in part to lowered levels of thyroid hormones). Environmental factors: Caffeine increases REE. Nicotine in cigarettes increases REE. Cold and hot weather increase REE. Altitude exposure increases REE. What E sources are used during rest? No need for ATP. Oxygen system is enough: CHO and fats can be used. On a mixed diet, 40% of REE is derived from CHO and 60% from fat. Increasing the %age of CHO or fat in the diet increase the contribution of one of them to the REE. After overnight fast, contribution of fat increases.  E sources used during rest The oxygen system is able to provide all necessary ATP for resting physiological processes. On a mixed diet, 40% of REE derived from CHO and 60% from fat. A diet rich in CHO or fat will increase the REE derived from CHO or fat respectively. When CHO levels are low (fasting), fat is more utilized. Metabolic Exercise Enzyme Energy Sport Activity Duration System Storage Activities location Form 0-4 sec Cytosol ATP, Creatine Field events, Power Phospate weight lifting 5-60 sec Cytosol Nonoxidative Muscle Track Sprints Speed glycogen and 1500-m run mitochondria liver glucose, Endurance muscle blood Oxidative and adipose lipids; muscle, blood and liver amino acids How do muscles influence the amount of E produced during exercise ? Rough estimate of REE: 1 C/kg/h. Adult male : 45% muscles. Adult female : 35% muscles. This proportion varies depending on level and type of physical activity. Human body possesses several different types of muscle fibers, and their primary differences are in the ability to produce E. How do muscles influence the amount of E produced during exercise ? Type Type I Type II a Type II b Twitch speed Slow Faster Fastest Color Red Red White Size Small Medium large Fatigability Slow Moderate Fast Oxidative processes Highest Moderate Lowest Mitochondria Highest Moderate Low Myoglobin Highest Moderate Low Blood flow Highest Moderate Lowest TG use Highest Moderate Lowest E for sports Aerobic capacity: Aerobic power: Anaerobic power: aerobic power anaerobic capacity anaerobic capacity Most muscles contain all 3 types of muscle fibers, and all fibers are used during ex of varying intensity. What effect does muscular exercise have on the metabolic rate ? The « exercise metabolic rate » (EMR) represents the increase in metabolism through about a moderate or strenuous physical activity = thermic effect of exercise ( TEE). Most important factor affecting the metabolic rate : intensity or speed of ex. Type I fibers predominate during low-intensity ex. Type II fibers predominate during more intense ex. Other considerations: Efficiency of movement. The more expert athlete do the activity with less effort. Air and water resistance. Body weight. How is exercise intensity measured ? Two general ways: I. Measure the actual work output or power of the activity (kilojoules/ sec or watts). II. Measure the physiological cost of the activity by monitoring the activity of the 3 human E systems. E produced from ATP-PCr system. Measurement of the concentration of lactic acid and determination of the « onset of blood lactic acid » (OBLA) or « lactate threshold » or “steady- state threshold”. Measure the maximal oxygen uptake to know the contribution of the oxygen system. highest amount of O2 that an individual may consume under ex situations = VO2 max (L/min or ml/kg/min) VO2 max: L/min 3.6 L 4L Kg body weight 60 80 VO2 max: ml 60 50 O2/kg/min How is the E expenditure of exercise metabolism expressed ? 4 ways: calories, kilojoules, oxygen uptake, METS. Met = unit that represents multiples of the resting metabolic rate. In our course, we will express exercise intensity in Cal/min based upon BW. 1 C= 4 Kj. 1 L O2 = 5 C. 1 MET = 3.5 ml O2/ kg BW / min (amount of O2 consumed during rest). How is the E expenditure of exercise metabolism expressed ? Given jogging = 0.08 kcal/lb/min. Determine the approximate Calories burned by a 130-pound male jogging for 45 minutes For a female swimmer who weighs 50 kilograms and possesses a maximal oxygen uptake of 3 liters, what is her maximal oxygen uptake expressed in milliliters per kilogram body weight? A person with a VO2 max of 3.5 L/min exercising at 60% of maximum. How much O2 (L/min) is used? How many calories per minutes are burned? How is the E expenditure of exercise metabolism expressed ? Example 1: E cost = 20 kj/min ➔ Cal/min? Example 2: exercise cost = 3 L O2/min ➔ Calorie cost? Example 3: exercise cost 25 ml O2/kg/min. W= 70 kg. determine total O2 cost/min by multiplying BW times O2 cost/kg/min. Example 4: exercise cost – 12 METS. W= 70 kg. Multiply total METS times O2 equivalent of 1 MET. How can i tell what my metabolic rate is during exercise ? Human body is basically a muscle machine designed for movement. Almost all the other body systems (nervous, CV, endocrine…) serve the muscular system. Because of some relationships among exercise intensity, O2 consumption and heart rate ,the average individual may be able to get a relative approximation of the metabolic rate during exercise. Intensity of ex inc. → O2 consumed inc. (by CV and respiratory systems). Maximal HR and VO2 max coincide at the same ex intensity level. Heart rate linearly related to O2 consumption and easy to measure at the wrist or neck pulse, but influenced by the type of exercise, level of physical fitness, sex, age… ➔ difficult to predict the exact metabolic rate from the heart rate. METs  Some activities are expressed in metabolic equivalents = METs  REE is approximately 0.0175 kcal/min/kg body wt.  Energy cost of activity in kcal = Assigned MET value X Body wt. (kg) X duration of activity/60 min Example  What is kcal the cost of activity for a person weighing 70kg exercising at an activity level of 5 METs for 40 minutes? 233 kcal or 5.8 kcal/min Calculate your exercise heart range  220 – age = X X is your maximum heart rate  Multiply your maximum heart rate X by 0.6. This is your lower-limit exercise  Determine your upper-limit exercise heart rate by multiplying your maximum heart rate by 0.9 What are the best types of activities to increase energy expenditure ? Activities that use the large muscle groups of the body and are performed continuously usually expend the greatest amount of calories. 1. Walking: 1. Approximately 1 cal/kg/mile walking at a speed of 2 -4 miles/hour. 2. Climbing stairs is one mean to make walking more vigorous. 3. Using small weights in conjunction with walking also increase E expenditure. 2. Running (1 Cal/kg/km): 1. Expend more E than walking the same distance (30-40% more). 2. Calorie cost of running a given distance doesn't depend on the speed. What are the best types of activities to increase energy expenditure ? 4. Swimming: because of water resistance, it expends more calories than walking and running. 4. Cycling : less E compared to running. 5. Group exercise : aerobic dance, cardio-kickboxing… approx. 10 Cal/ min. 6. Home aerobic exercise equipment: treadmill running burn the most calories for any given level of perceived effort. 7. Resistance or weight training: effective to expand E but less than aerobic types of ex. Does exercise affect my resting energy expenditure (REE)? Ex increases metabolic rate during ex and during the recovery period. Increase in body temperature. Increase in circulating hormones. = metabolic after effects of exercise. EPOC = excess post exercise O2 consumption = amount of O2 in excess of the preexercise REE, that reflects the additional caloric cost of the ex above and beyond that expended during the ex task itself. Not a very significant contribution to weight loss, but prevents the decrease in REE seen in individuals on VLCD diets. How much E do i need to consume daily ? Estimated energy requirements (EER) = dietary intake that is predicted to maintain E balance in a healthy adult. It estimates REE + PA or thermic effect of exercise. Total daily E expenditure (TDEE)= BEE + TEF + TEE. BEE: 60-75%. TEF: 5-10%. TEE: 15-30% (can range from near 0 in sedentary to > 50% in athletes) Effect of PA on TDEE determined by the physical activity level (PAL). Non exercise activity thermogenesis (NEAT) = energy expended that is not sleeping, eating or sports related exercise (e.g: walking to the car, typing…) (PAL in sedentary people category). What E systems are used during exercise ? Most important factor is the intensity of the exercise = rate = speed= tempo. The faster you do something, the higher the rate of E expenditure , the more rapid you produce ATP. All 3 systems – ATP-PCr, lactic acid, O2 - are used in one way on another during most athletic activities, but the 2 first are able to produce ATP rapidly in high intensity events, for short periods (anaerobic). ATP-PCr predominate in short powerful muscular activities (10 sec). Lactic acid system predominate during longer and middle distance sprints (30-120 sec). The O2 system possesses a lower rate of ATP production than the other 2 systems, but its capacity for total ATP production is much greater (lower intensity ex). O2 system can be improved through a physical conditioning program.  10 30 60 120 Time 10 s 1 min 2 min 4 min min min min min Anae- 85 70 50 30 15 5 2 1 robic Aero- 15 30 50 70 85 95 98 99 bic What E sources are used during exercise ? ATP- PCr system use ATP and phosphocreatine Lactic acid system uses only CHO (+++ muscles gly stores). O2 system uses CHO (muscle gly, liver gly, BG) and fat (muscles and AT TG) primarly, and prot also. Determination of the E source depends on intensity and duration. For moderate exercise ( app 50% VO2 max), BG and fat may provide much of the needed E. If > 50% VO2 max, body begins to rely more on intramuscular stores of gly and TG. As intensity continues to increase, body relies more and more on CHO (muscle gly). This transition from use of fat to CHO during increase of intensity is called cross over concept. In events of long duration, body stores of CHO are depleted and the primary E source is fat. Training in the “fat-burning zone” for weight loss is a myth. What is fatigue ? Chronic fatigue: +++ in endurance athletes. Involve: Overreaching: physical and mental stress that may impair physical performance. Overtraining: syndrome involving prolonged periods of fatigue (uncertainty of its presence; it’s probably under recovery). Associated with disturbances of the immune system, infections, mental stress, personality traits. Treatment: behavioral therapy and graded exercise. Not very prevalent. Occurs +++ in females, 40-50 years old. What is fatigue ? Acute fatigue: Inability to continue exercising at a desired level of intensity. ATP production rates are unable to match ATP utilization rates. Central fatigue involves the brain or spinal cord of the CNS. Peripheral fatigue associated primarily with the muscles and sometimes with other organs such as heart or lungs. What causes acute fatigue in athletes ? Mechanism not fully understood, depends on the type of exercise, state of fitness, and fiber-type composition of the muscle. Peripheral fatigue: occurs when: Compounds to produce ATP are depleted. By-products of metabolism accumulate in the muscle and interfere with optimal energy metabolism +++ role of calcium in muscle contraction. Central fatigue: occurs with substrate depletion and by-products accumulation (e.g: high levels of serotonin). Lactic acid disturb muscle cell homeostasis How can i delay the onset of fatigue ? Proper training: Physiologically: training for each E system to increase its stores and metabolic efficiency. Psychologically: tolerance of stress. Biomechanically: to maximize the mechanical skills (e.g changing body fat and muscles). Proper nutrition with adequate supply of nutrients.