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METABOLISM 2 Metabolism in physical activity © Katarína Babinská MD, PhD, MSc, Institute of Physiology CU, Bratislava Energy sources for the human body - the cells can directly utilize only energy gained by hydrolysis of high energy bonds - ATP – adenosine triphosphate - universal source of energy in the human body - adenine + ribose + 3 phosphates - hydrolysis of ATP ADP + P + 50,2 kJ AMP + P + 50,2 kJ - 2 high energy bonds (last 2 phosphates) - energy for synthesis of substances with high energy bonds is gained by utilization of energy from chemical bonds of nutrients: protein, fat, carbohydrates (and alcohol) - energy is released from nutrients (fuels) in oxidation main products: energy (ATP), H2O, CO2 - energy value of nutrients – amount of energy liberated by oxidation of 1 g of a nutrient in the human body (physiological free E) - physical free energy – amount of heat liberated by burning (oxidation) of 1 g of nutrients in calorimeter P,F,C free energy carbohydrates fat protein (alcohol physical 17 kJ 38 kJ 23 kJ 29 kJ physiological 17 kJ 38 kJ 17 kJ * 29 kJ) Carbohydrates and fats - fully oxidized in the body (CO2, H2O), therefore - physiological free energy = physical free energy Proteins • not completely oxidized in the body • end products of their oxidation include – H2O, CO2 and energy – also nitrogen containing substances (urea, ammonia, etc.) P,F,C • excreted from the body by urine - their bonds contain certain amount of energy • physiological free energy of proteins < physical free energy of proteins free energy carbohydrates fat protein (alcohol physical 17 kJ 38 kJ 23 kJ 29 kJ physiological 17 kJ 38 kJ 17 kJ * 29 kJ) Types of energy balance E equilibrium: E intake = E expenditure - optimal for a healthy individual positive E balance: E intake > E expenditure - excess energy is stored - body fat (main form of stored energy – 75% of supplies) - glycogen (1% of stores) - leads to weight gain (may be desirable or undesirable) negative E balance: E intake < E expenditure - the energy deficit is compensated by depletion of stored forms of energy (glycogen, fat, protein) - leads to weight loss (may be desirable or undesirable) Fed state and fasted state metabolism Energy expenditure: continuous process Energy intake: 3-5x /day 0 4 8 12 16 20 Storage forms of energy adipose tissue 75 % of stores - glycogen (1% of stores - liver, muscles) - proteins – 24 % (waste of active tissues) - high energy bonds: ATP, phosphocreatinine, etc.. – very limited supplies - Depending on substrate availability: catabolism or anabolism prevails (fed state metabolism, fasting state metabolism) 24 (h) Fed state metabolism • 4 hours after food ingestion • metabolic fuels are absorbed and enter the circulation • regulation of metabolism is determined primarily by the influx of glucose from the gut into blood Hormonal regulation • Insulin is released (in response to increased glucose level), • glucagon level drops down http://www.austincc.edu/apreview/EmphasisItems/Glucose_regulation.html Fuel utilization • plentiful supply of glucose - becomes the main fuel for the tissues • insulin stimulates – uptake od glucose by muscle - becomes the preferred fuel for the muscle – synthesis of glycogen in both liver and muscle – glucose uptake into adipose tissue for triacylglycerol synthesis – uptake of AA leading to and increased rate of protein synthesis • most of the absorbed triacylglycerols travel to adipose tissue for storage • the fatty acid and TAG synthesis in liver is increased (in response to increased glucose availability) – exported in VLDL to periphery – available as metabolic fuels for peripheral tissues – stored in adipose tissue Fasting state metabolism • begins about 4 hours after last meal • nutrient levels in blood drop down Hormonal regulation • detemined primarily by the disappearance of glucose from the blood - signalling the end of fuel absorption from the gut • drop in insulin blood level • rise in glucagon level • fasting is stressful – epinephrine plays a role in fasting state metabolism Fuel utilization Glucagon causes stimulation of: – glycogen breakdown in the liver to release glucose into circulation – lipase in the adipose tissue resulting in release of free fatty acids – gluconeogenesis from amino acids and pyruvate Reduced level of insulin causes – reduced rate of glucose uptake by the skeletal muscle – reduced AA uptake into muscle and lower protein synthesis, so that AA are available for gluconeogenesis • tissues (other than brain and red blood cells) utilize preferentially fatty acids to spare glucose for the brain and RBC • liver - synthesis of ketones (because of a greater capacity to oxidize fatty acids then required to meet its own energy requirements) – for use as a metabolic fuel for other tissues (including brain) Metabolic rate and physical activity Physical activity • immediate increase in energy expenditure/ metabolic rate • an immediate increase in demand for a/ fuels b/ oxygen Metabolic rate physical activity kJ resting state 0 time (min) Energy sources for the muscle in physical activity 1. Phosphagen system (ATP + PC) ATP - first source of energy for the muscle contraction - stores of ATP in muscles – sufficient for 1-3 sec. Phosphocreatine (PC) - cannot be utilized directly ATP creatine ADP+ P + E phosphocreatinine - serves for fast re-synthesis of ATP from ADP ATP and PC supplies for 8 – 10 s Main source of energy in short-lasting intense physical activity Subsequently proteins, fats and carbohydrates are being utilized 2. Anaerobic metabolism 3. Aerobic metabolism Reaction of the body to physical activity - sudden increase of requirements for O2 - systems that help to supply O2 into the muscle are activated increase of ventilation (tidal volume and frequency) higher cardiac output per minute (frequency and stroke volume) blood re-distribution into the muscle higher uptake of oxygen from blood Metabolic rate physical activity kJ resting state 0 time (min) - due to gradual activation of systems involved in O2 supply, the O2 availability increases gradually - in the early stage of physical activity the supply of O2 is lower than the requirements for O2 - oxygen reserve is used haemoglobin - higher O2 uptake by tissues - decrease of haemoglobin oxygen saturation (venous blood) myoglobin utilization of physically dissolved O2 uptake of oxygen from the lungs is higher - Reserve is insufficient - oxygen deficit is established A 96% V 75 % A 96% V 50 % Oxygen deficit - is the difference between the higher O2 requirements for the physical activity and insufficient O2 that is supplied - consequence: energy, or its part, must be provided by anaerobic metabolism - the proportion of aerobic metabolism is gradually increasing Energy gain in anaerobic metabolism of glucose Anaerobic - glucose pyruvate lactate - fast source of energy - less efficient 1 mol of glucose : 2 moles of ATP 1 mol of glycogen : 3 moles of ATP Aerobic – 36 moles of ATP Steady state -achieved approx. after 3-5 minutes of exercise - O2 supplied into working muscle is adequate to metabolic requirements 3. Aerobic metabolism - utilization of glucose, fatty acids Utilization of substrates in physical activity Recovery period - physical activity is finished - oxygen consumption remains higher and only gradually decreases to resting values Oxygen debt -is repaid = volume of O2 consumed in recovery period above baseline consumption Excess oxygen is used to replenish the O2 supplies - haemoglobin - myoglobin - O2 dissolved in blood to replenish the stores of ATP, PC for re-conversion of lactate to pyruvate myoglobin haemoglobin Recovery (restoration) period -heart rate, frequency of breathing are dropping down - the restoration period is finished when preexercise heart rate and breathing frequency is reestablished Maximal oxygen consumption (maximal aerobic capacity) -VO2max - is the maximum capacity of an individual's body to transport and use oxygen during exercise - reflects the physical fitness of the individual, can improve with training - depends on age, body size and composition (lean body mass), genetics, altitude, environmental temperature - expressed either in litres of oxygen per minute (l/min) or as millilitres of oxygen per kilogram of bodyweight per minute (ml/kg/min) - values (ml/kg/min) average: males 45 athlets: males > 60 - in physical activities with oxygen requirements exceding VO2max part of the energy is derived in anaerobic processes females 40 females >55 Light/medium physical activity (activities not reaching VO2max ) steady state is achieved in a heavy physical activity no steady state occurs (if maximum aerobic capacity is exceeded) replenishing of oxygen takes longer time (i.e. the restoration period is longer) Efficency of the physical work when an individual performs physical activity only part of the total energy expenditure is used for external work (exercise), the remainder appears as heat external work exercise Nett efficiency of = _____________________________________________________________ the physical work net energy expenditure for the physical activity* heat *energy expenditure that is above resting metabolic rate Dynamic activities - average efficiency 25% = 0,25 - i.e. 25 % of the metabolized energy is utilized for performing the physical work and 75 % is transfromed to heat Static activities -efficiency 0% -all the energy released in metabolism is converted into heat Metabolism during physical work, determination of oxygen debt and efficiency of work Task 1. assess energy expenditure (metabolic rate) per 1 minute and evaluate the intensity of the physical activity 2. calculate the oxygen debt 3. determine the efficiency of physical work 4. calculate the pulse oxygen Method: indirect calorimetry Measurements (in 3 time periods): - time volume of expired air (into Douglas bag) O2 in the expired air CO2 in the expired air heart rate 1 2 3 Energy cost of physical activity Procedure – examination takes place in 3 time periods 1. resting state – 5 minutes - the volunteer is sitting, he expires air into Douglas bag - measure the heart rate - after you collect the expired air - immediately do the measurements: V, O2, CO2 2. physical activity – 3 minutes - cycling on a stationary bicycle – low effort is recommended - the expired air is collected in a Douglas bag - measure the heart rate - !!! after the 3 min period is over – immediately close the Douglas bag and connect the tube to another bag 3. restoration period - the volunteer is sitting and resting - measure heart rate every minute - when the heart rate returns to resting values – restoration period is finished – finish the measurement 1 2 3 Energy cost of physical activity Calculations Period 1 Rest Duration of the period (min) V - volume of ventilated air (L) O2 consumption - O2 (%) CO2 production - CO2 % Average heart rate (beats per minute) Period 2 Exercise Period 3 Recovery Calculations Period 1 Rest O2 consumption in entire period (L)= = volume of ventilated air(L) . O2 (%) O2 consumption per 1 minute (L)= = O2 consumption in entire period (L) / duration of the period (min) CO2 production in entire period (L)= = volume of ventilated air (L). CO2 (%) CO2 production per 1 minute (L)= = CO2 production in entire period (L) / duration of the period (min) Period 2 Exercise Period 3 Recovery Calculations O2 debt (L) = O2 consumption in the entire period 3 (L) – O2 consumption in entire period 1 (L) total O2 consumption for physical activity (L) = = O2 consumption in period 2 (L) + oxygen debt (L) O2 consumption for 1 minute of physical activity (L) = = O2 consumption in period 2 (L) + oxygen debt (L) total CO2 production for physical activity (L) = = CO2 production in period 2 (L)+ CO2 production in period 3 (L) - CO2 production in period 1 (L) Preexercise Period 1 RQ Energy equivivalent - EE (kJ/ L) Metab. rate per 1 minute (of period 2) (EE . O2 consum. per 1 min) (kJ) Total – for the pysical activity Calculations Net energy for physical activity per minute (kJ)= = metab. rate in exercise per 1´(kJ) – preexercise metabolic rate per 1´(period 1) (kJ) Net energy for physical activity (3 minutes) (kJ) = Net energy for physical activity per minute (kJ) . 3 Work output during the exercise (kJ) (formulas in the manual - step 18) Net efficiency of the work = work output during the exercise / net energy for physical activity Physical activity Pre-ecercise/resting metabolic rate Net energy for physical activity Metabolic rate in physical activity Period 1 Rest Pulse oxygen (ml/ 1 systole) = O2 consumption per 1 minute (mL)/ average heart rate (beats per minute) Period 2 Exercise Period 3 Recovery Use the following table and evaluate the intensity of physical activity performed by the examinee Intensity of physical activity Energy expenditure (kJ min-1) very light up to 4.2 light 4.2 - 12.6 moderate 12.6 - 20.9 medium 20.9 - 33.5 heavy 33.5 - 41.9 vigorous 41.9 - 62.8 extremely heavy 62.8 or more Intensity of the physical work estimated from the amount of energy expended over resting metabolic rate (netto kJ)