2.25.14 kin 470 class notes- Upward drift in oxygen uptake during prolonged exerciseo Oxygen consumption drifts up – using more energy to keep body cool (costs energy)- Changes in oxygen uptake with incremental exerciseo Plateaus – VO2 maxo VO2 vs. work rateo Look for someone to plateau in lab this weeko Exercise really hurts – you are going to want to stopo Keep going… only way to see plateauo Aerobic energy productiono Looking at 2 mins before systems are depleted- Changes in blood lactate concentration during incremental exerciseo Increases slowly until about 50% of VO2 max, after that it changes to amuch steeper slope – greater increase with workloado Lactate threshold – point where slope increases- Lactate thresholdo Low muscle oxygeno Accelerated glycolysiso Recruitment of fast-twitch fiberso Reduced rate of lactate removal- Practical uses of lactate thresholdo Prediction of performance Better than VO2 maxo Planning training programs Marker of training intensity- OBLAo Onset of blood lactate accumulation- 4mM- The Cori Cycle: Lactate as a Fuel Sourceo Lactic acid produced by skeletal muscle is transported to the livero Liver converts lactate to glucose Gluconeogensis Glucose is transported back to muscle and used as fuel Lactate-shuttle hypothesis- Liver not necessarily incolved- LA fuel source for other tissues- Lactate shuttle hypothesiso Heart Readily use lactate pyruvate Explains phenomena of how quickly we get rid of lactate- Blood lactate removal following strenuous exerciseo If you run and sit in stands and wait, lactate stays higho Jogging gets rid of lactate fastero Sitting and doing nothing will take longer to get rid of lactate- Sources of fuel during exerciseo CHO Blood glucose Muscle glycogeno FAT Plasma FFA (from adipose tissue lipolysis) Intramuscular triglycerideso PRO Small contribution to total energy production (~2%) May increase duing very long exerciseo Blood lactate Gluconeogenesis- Estimation of fuel use during exerciseo Respiratory exchange rate (RER or R)o RER: indicated fuel useo During steady state exercise VO2 = O2 consumption in cells VCO2 = production by cellso Sensor using in lab: 2 sensors One for oxygen, one for carbon dioxide Assumes no protein utilizationo Estimation of fuel utilization during exercise RER- R = VCO2/Vo2 R for fat- Glucose + 23 O2 16 CO2 + 16 H2O- R = .70- Means you are burning 100% fat R for carbs- Increase intensity- Glucose + 6 oxygen 6 Co2 + 6 H2O- R = 1.00- Means you are burning 100% carbs- Exercise intensity and fuel selectiono Low intensity exercisees (< 30% VO2 max) Fats are primary fuel sourceo High intensity = CHO is primary fuel source- Crossover concepto Mechanisms of increase CHO uses Rate of energy > fats can provide Increase recruit fast muscle Increase epinephrine release- Influence of exercise intensity on muscle fuel sourceo Percentage of total fuel sourceo At 100% for each intensityo Within bars – see where and what we are burningo Low intensity Little muscle triglycerides Mostly burning plasma FFA Small plasma glucose Small muscle glycogeno Middle FFA goes way down Glucose stays same Muscle glycogen goes way upo High Dramatic at 85% of VO2 max High amount of muscle glycogen- Interaction of fat and CHO metabolism during exerciseo Fats burn in a CHO flameo Glycogen (CHO) is depleted during prolonged high-intensity exercise- Resultso Decrease rate of glycolysis leads to decrease production of pyruvate- Best exercise intensity for weight management?o Low intensity exercise? Greater proportion of fat used to perform exercise! 83% (low intensity) vs. 42% (high intensity)o but total energy used is higher in higher energy exercise- The regulation of muscle glycogen breakdown during exerciseo Very precisely controlledo Increase in epinephrine Stimulates signaling cascade increase in cAMPo Increase intracellular calcium Increase calmodulin activation Lots of calcium around Stimulates independent pathway ^ Cause phophorylase(active) This is the dominant pathway Contracting calcium levels go up Glycolysis stimulated faster than epinephrine releasedo As you exercise more intensely, release more and more epinephrine At higher intensities, this mechanism takes over- Clinical applications 4.1o McArdle’s Syndrome: genetic error in muscle glycogen metabolismo Lack of phosphorylaseo Can’t break down glycogeno Healthy subjects do hand grip exercise Lactate and fatigue go way upo Patient Does the exercise No increase in lactic acid Comes from idea that they lack phosphorylase or don’t respondto it Blood lactate levels never rise Lactic acid is not linked to fatigue They are really compromised in terms of exercise capacity – can’t sprint etc Can never get to higher
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