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Blood Lactate Accumulation and Removal

Blood Lactate Accumulation and Removal. Effects on Blood Lactate Concentration. Lactate Response to Prolonged Exercise (70% of VO 2max ). (Kolkhorst & Buono, Virtual Exercise Physiology Lab , 2004). Lactate Response to Prolonged Exercise.

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Blood Lactate Accumulation and Removal

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  1. Blood Lactate Accumulation and Removal Effects on Blood Lactate Concentration

  2. Lactate Response to Prolonged Exercise(70% of VO2max) (Kolkhorst & Buono, Virtual Exercise Physiology Lab, 2004)

  3. Lactate Response to Prolonged Exercise

  4. Lactate Response to Incremental Exercise(endurance-trained athlete) (Kolkhorst & Buono, Virtual Exercise Physiology Lab, 2004)

  5. Anaerobic Threshold: Does it Exist?(or blood lactate inflection point?) • Wasserman et al. (1973) proposed that muscle became hypoxic at higher intensities and thus produce ATP and lactate anaerobically as well as  VE • Challenges to Wasserman theory • McArdle's syndrome patients lack phosphorylase • still demonstrate VT • does muscle become hypoxic? • are there other factors that explain the sudden increase in blood La?

  6. Mitochondrial PO2 during exercise Relationship between mitochondrial VO2 and PO2. Critical mitochondrial PO2 is around 1.0 torr. Muscle intracellular PO2 and net lactate release. Note that PO2 remains above critical mitochondrial O2 tension (1 torr).

  7. Motor Unit Recruitment Pattern -- Size Principle

  8. La and EPI Response to Exercise La EPI

  9. Metabolic Fate of Lactate

  10. Lactate Shuttle

  11. Cori Cycle

  12. Influence of exercise intensity on rate of blood La clearance during recovery

  13. Metabolic Fate of Lactate • During exercise: • ~¾ oxidized by heart, liver, and ST fibers • During recovery: • oxidized by heart, ST fibers, and liver (1 fate) • converted to glycogen • incorporated into amino acids • La metabolism depends on metabolic state

  14. Fate of lactate under three conditions 4 hr after injection. Note that oxidation is the 1 pathway of removal.

  15. Effect of Altitude on La Response At altitude: • blood [La] is higher at same absolute workloads • muscle blood flow similar at same absolute workloads • La threshold occurs at same relative intensity • EPI threshold occurs earlier at altitude • Lactate paradox – peak [La] is less under hypoxic conditions than at normoxia

  16. Determining lactate turnover during exercise: tracer methodology • use naturally occurring isotopes • 13C and 2H isotopes most commonly used • pulse injection tracer technique • isotopically-labeled La added to blood in single bolus • concentration measurements taken over time • rate of concentration decline represents turnover rate

  17. Pulse injection tracer technique

  18. Continuous-infusion tracer techniques • Continuous-infusion technique • isotopically-labeled La added at increasing rate until equilibrium point is reached • La appearance = La removal • Primed continuous-infusion technique • priming bolus of isotopically-labeled La added initially • speeds time to reach equilibrium • remaining isotopically-labeled La added at continuous, constant rate • [isotope] depends on rate of infusion and volume of distribution (estimated)

  19. Continuous infusion tracer technique

  20. Primed continuous-infusion technique(used by Stanley et al. and MacRae et al.) • turnover rate = appearance - disappearance • Ra dependent on: • volume of distribution • arterial [La] • Rd = Ra minus arterial [La] • metabolic clearance rate (MCR) = Rd / [La] • calculates La clearance rate relative to arterial [La] • increasing MCR indicates Rd is dependent upon [La]

  21. Read one of the following articles for next Tuesday Holden, S.-MacRae, S.C. Dennis, A.N. Bosch, and T.D. Noakes.  Effects of training on lactate production and removal during progressive exercise in humans.  J. Appl. Physiol. 72: 1649-1656, 1992. Stanley, W.C., E.W. Gertz, J.A. Wisneski, D.L. Morris, R. Neese, and G.A. Brooks.  Systemic lactate turnover during graded exercise in man.  Am. J. Physiol. 249 (Endocrinol. Metab. 12): E595-E602, 1985.

  22. Lactate response to graded exercise(Stanley et al., JAP, 1985) • Ra and Rd exponentially related to VO2 • linear relationship between arterial [La] and Ra • curvilinear relationship between arterial [La] and Rd

  23. Rates of blood lactate appearance (Ra) and disappearance (Rd) during graded exercise before and after training MacRae et al., JAP, 1992

  24. Training adaptations to lactate kinetics(MacRae et al., JAP, 1992) • submaximal Ra  by training • peak Ra similar regardless of training status • at same relative intensities, Ra was  at <60% and similar at >60% • Rd  by training • peak Rd  • at same relative intensities, Rd was similar at <60% and  at >60% • MCR  at higher exercise intensity and  with training

  25. 65% pre-training 65% post-training – same relative workload 45% post-training – same absolute workload 45% pre-training Effect of training on blood lactate response

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