PET3380C Chapter 7 Book Notes Immediate Energy The ATP PCr System short term high intensity exercise comes almost exclusively from the intramuscular high energy phosphate sources adenosine triphosphate and phosphocreatine Short Term Energy The Lactic Acid System the energy to phosphorylate ADP during such exercise comes mainly from stored muscle glycogen breakdown via anaerobic glycolysis and results in lactate formation large rapid accumulations of blood lactate occur during maximal exercise that lasts between 60 and 180 seconds decreasing the intensity of such exercise to extend the exercise period correspondingly decreases the rate of lactate accumulation and the final blood lactate level Lactate Accumulation blood lactate does not accumulate it does still form at all levels of exercise the more intense the exercise the more lactate accumulates when glycolytic metabolism predominates NADH production exceeds the cell s capacity for shuttling its hydrogens electrons down the respiratory chain because of insufficient oxygen supply at the tissue level the imbalance in hydrogen release and subsequent oxidation ie the NAD NADH ratio causes pyruvate to accept the excess hydrogens two the new pyruvate with two additional hydrogens forms lactate for untrained people lactate begins to rise at about 50 to 55 of their VO2 max for trained individuals lactate begins to accumulate at about 75 of their VO2 max they have a higher blood lactate threshold use glucose and fatty acid catabolism maintain a lower level of lactate which conserves glycogen reserves under aerobic conditions 70 lactate is oxidized by other tissues 20 is converted to glucose in muscle and the liver and 10 is converted to amino acids ie there is no net gain of lactate blood lactate only accumulates when its disappearance oxidation etc does not match its production ie your producing more than you can get rid of another factor for lactate accumulation is the muscle type fast twitch fibers favor the conversion of pyruvate to lactate slow twitch fibers favor the conversion of lactate to pyruvate on the other hand trained athletes perform at higher steady rate intensities than untrained individuals most likely related to three factors their specific genetic endowment ie percentage of specific fibers their born with specific local training adaptations that favor less lactate production more rapid rate of lactate removal at any exercise intensity also a side note capillary density size and number of mitochondria increases with training as well as the concentration of enzymes and transfer agents in aerobic metabolism producing high blood lactate levels during maximal exercise increases with specific sprint power anaerobic training and decreases when the training stops sprinters often achieve 20 to 30 higher lactate levels than untrained individuals there are three possible mechanisms improved motivation that accompanies exercise training increased intramuscular glycogen stores that accompany training training induced increase in glycolytic related enzymes the 20 increase in glycolytic enzymes falls well below the two to threefold increases in Lactate Producing Capacity Chapter 7 Book Notes PET3380C aerobic enzymes with endurance training Long Term Energy The Aerobic System because glycolytic reactions produce relatively few ATP aerobic metabolism provides nearly all of the energy transfer when intense exercise continues beyond several minutes Oxygen Consumption During Exercise pulmonary oxygen uptake steady state rate oxygen consumption increases rapidly until it reaches this steady rate this reflects the balance between energy required by the working muscles and ATP refers to the flat portion plateau of the oxygen consumption curve oxygen consumption by the lungs production in aerobic metabolism no appreciable blood lactate accumulates under steady rate aerobic metabolic conditions so theoretically a person could go forever if they wanted to excluding environmental influences fluid loss electrolyte depletion and etc highly trained individuals can maintain a steady rate for long periods of time at higher intensities this is because the high capacity of the central circulation to deliver oxygen to working muscles the high capacity of the exercised muscles to use available oxygen Oxygen Deficit the oxygen consumption curve does not increase instantaneously to a steady state though the energy requirement remains the same throughout the exercise oxygen consumption remains below the steady level during the transitional stage this is because no matter how much oxygen is available to the body it still begins with the process of anaerobic breakdown of ATP hydrogen production and subsequent oxidation become proportional to the exercise energy requirement after several minutes of submaximal exercise the difference between the total oxygen consumption during exercise and the oxygen deficit total that would be consumed had steady rate oxygen consumption been achieved from the start it represents the immediate anaerobic energy transfer from the hydrolysis of intramuscular high energy phosphates and glycolysis until steady rate energy transfer matches the energy demands energy for exercise does not simply occur from activating a series of energy systems that switch on and switch off but rather from smooth blending with considerable overlap of one mode of energy transfer to another Oxygen Deficit in the Trained and Untrained the endurance trained person reaches steady rate more rapidly with a smaller oxygen deficit than sprint power athletes cardiac patients and the untrained more rapid increase in muscle bioenergetics increase in overall blood flow cardiac output disproportionately large regional blood flow to active muscle complemented by cellular adaptations Maximal Oxygen Consumption maximal oxygen consumption VO2 max only slightly with additional increases in exercise intensity it provides a quantitative measure of a person s capacity for aerobic ATP resynthesis when oxygen consumption plateaus or increases Fast and Slow Twitch Muscle Fibers fast twitch FT or type 11 type 11a type 11b a type of muscle fiber that has two subdivisions rapid contraction speed high capacity for both anaerobic and aerobic ATP prod rapid contraction speed Chapter 7 Book Notes PET3380C these fibers become active during stop and go activities they increase force output when facing an increasing challenge slow twitch ST or type 1 relatively slow contraction
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