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Exercise Metabolism Concepts Dr. Suzan Ayers Western Michigan University Lecture Overview Energy production Oxygen supply during sustained exercise Measuring exercise capacity Cardiorespiratory system and oxygen supply during exercise Human skeletal muscle cells Activity’s energy cost Dietary considerations Sport-specific training NOTE: throughout this presentation, the use of [] connotes “concentration” Energy Production Adenosine triphosphate (ATP) 3 ATP-resynthesizing energy systems (Fig 10.4) Immediate energy system (stored energy, high-energy phosphagen, ATP-PCr system) 0-30s Anaerobic glycolytic system (lactic acid system) 20-180s Aerobic or oxidative system >3 min (see Table 10.1) All work along a continuum (fig 10.4) constantly Body breaks down nutrients (fats, proteins, carbs) to release energy from chemical bonds, which is then used to synthesize ATP Max exercise can produce 15-fold ↑ [lactic acid] 20-40 mins required to fully remove this lactic acid build-up Light jog @ 30-60% max pace best active recovery Oxygen Supply: Sustained Exercise Oxygen consumption: VO2 O2 deficit Submaximal, [↔] exercise initial few mins of exercise, insufficient O2 uptake ATP provided by 2 anaerobic systems Period of adjustment for increased energy demand VO2 steady state reached Continually [>] exercise VO2 increases steadily to max value/exercise capacity Supramaximal exercise (above VO2max) Post-exercise O2 uptake ATP, beyond that produced by oxidative metabolism, produced by anaerobic glycolysis (↑ lactate levels) EPOC: excess post-exercise O2 consumption (O2 debt) Excess O2 removes lactate & re-synthesizes muscle stores of glycogen, PCr and ATP Size of EPOC depends on [exercise]/duration VO2max: Indicator of endurance ex capacity Max O2 consumed/min during exercise (aerobic power) 40-50% genetically determined May increase up to 40% w/ training Not exclusive indicator of exercise performance Measuring Exercise Capacity: Aerobic or Endurance Capacity VO2 max: measure of aerobic power Endurance exercise capacity: performance measure Mode of testing specific to athlete’s training VO2 max usually reached during final minute of exercise, immediately before volitional fatigue Major limiting factor for endurance exercise performance is O2 delivery via the circulatory system to the working muscles Measuring Exercise Capacity: Anaerobic Capacity Anaerobic power: max power, possible in all-out exercise test Anaerobic capacity: total work accomplished in a set time (30-60s) General or sport-specific tests used 10- and 30-s cycle ergometer tests Vertical jumping Sprinting Stair climbing Both (an)aerobic tests help standardize [exercise] for exercise prescription Cardiorespiratory System and Oxygen Supply During Exercise Cardio: heart Vascular: blood vessels Respiratory: lungs and ventilation Aerobic: with oxygen Overall, HR, blood flow, & respiratory rate ↑ proportionally with ↑ [exercise] Blood flow during submax exercise, ~50-60% of blood flow is directed to working muscles during max exercise, ~80% of blood flow is directed to working muscles Human Skeletal Muscle Cells Fiber types are classified by (Table 10.2): Physiological (activities, functions) Biochemical (chemistry of biological processes) Histological (microscopic structure) properties Motor neuron determines fiber type I (slow oxidative): smaller, ↓ force, ↑ time, posture IIa (fast oxidative glycolytic): large, fast, ↑ force, ↑ gylcolytic capacity, moderate: mitochondria, capillary supply, oxidative capacity than IIb fibers IIb (fast glycolytic): largest, fastest, most forceful, ↑ anaerobic glycolytic capacity, fatigue easily Fiber types activated proportionally to force Size principle: I, then IIa, then IIb (as additional force needed) Average human: 50% ST, 50% FT Proportion of fiber types varies Elite distance runners: 80% I, 20% II Elite sprinters: 25-40% I, 60-75% II Fiber types only a broad indicator of potential Activity’s Energy Cost Influential factors Activity, intensity, mechanical efficiency Body mass (non-supported activities-run, walk) Environmental factors (temperature, wind, rain) Human body, at best, 25% efficient Economy of movement: O2 cost of any activity Body mass supported: energy cost independent of body mass Unsupported activities: energy cost rises w/ ↑ body mass Most energy consumptive: whole body or large muscle group activities (swim, run) Consider energy cost of training in development of dietary planning Dietary Considerations High carbohydrate (CHO) diet ↑ muscle glycogen stores (ergo exercise capacity) Fig.10.14 “Hitting the wall”=glycogen depletion 24-48hr required to fully restore glycogen levels ↑ CHO diet ASAP after exercise aids repletion rate 60-80% daily intake=CHO Sports drinks, fruits, breads, wheat cereals, gels 6-8g CHO/kg body wt/day Intense training or taper times 9-10g CHO/kg body wt/day Protein Tables 10.4, 10.5 Well-balance diet adequate for most athletes 12-15% daily intake=protein (0.8g protein/kg/day) Strength/Power/Speed athletes 1.5-2 g protein/kg body wt/day Endurance athletes 1.5-1.6 g protein/kg body wt/day EXCESS PROTEIN = EXPENSIVE URINE Water 70-80% energy produced during ex is heat (sweat) Depending on factors, 0.5-3L/hr sweat can be lost Losing 4-5% body mass impacts thermoregulation and exercise capacity Prolonged exercise w/o H20 replacement Blood volume may drop significantly Heat loss slows/stops Body temp can ↑ dangerously Guidelines 500-1000ml pts plain H20 1hr before activity 250-500ml 20 mins before 250ml every 15 mins during Intense exercise > 60 mins: add glucose & electrolytes 6% glucose in solution--[low electrolyte] promotes faster H20 absorption Several hrs may be needed to completely replace H20 Sport-Specific Training Anaerobic Max force production (Abernathy:0-30 sec) Stored ATP and PCr, muscle glycogen breakdown Anaerobic glycolysis Up Energy Training to 2 min events (Abernathy:20-180 sec) Limited support for training benefits here Aerobic Energy Training (Abernathy:0-30 sec) Evidence clear, dramatic, specific Endurance training has specific benefits volume in muscle ↑enzyme activity in aerobic pathways ↑fiber’s ATP generating ability aerobically ↑# capillaries fueling each muscle fiber ↑intramuscular fat stores improves fat burning ability Improves muscle’s ability to access & utilize fat ↑mitochondrial Endurance training has general benefits volume 10-15% ↑stroke volume ↑cardiac output (HR x stroke volume) ↑efficiency of the respiratory system ↑blood More air with fewer breaths Greater tidal volume Ventilation=tidal volume x frequency