Blood Lactate Accumulation and Removal

Effects on Blood Lactate Concentration

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Lactate Response to Prolonged Exercise(70% of VO2max)

(Kolkhorst & Buono, Virtual Exercise Physiology Lab, 2004)

Lactate Response to Prolonged Exercise

Lactate Response to Incremental Exercise(endurance-trained athlete)

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% of VO2max

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(Kolkhorst & Buono, Virtual Exercise Physiology Lab, 2004)

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?

Muscle intracellular PO2 and net lactate release. Note that PO2 remains above critical mitochondrial O2 tension (1 torr).

Relationship between mitochondrial VO2 and PO2. Critical mitochondrial PO2 is around 1.0 torr.

Mitochondrial PO2 during exercise

Motor Unit Recruitment Pattern -- Size Principle

La and EPI Response to Exercise

La

EPI

Metabolic Fate of Lactate

Lactate Shuttle

Cori Cycle

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

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

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

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

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

Pulse injection tracer technique

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)

Continuous infusion tracer technique

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]

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.

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

Rates of blood lactate appearance (Ra) and disappearance (Rd) during graded exercise

before and after training

MacRae et al., JAP, 1992

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

Effect of training on blood lactate response

65% pre-training

65% post-training – same relative workload

45% post-training – same absolute workload

45% pre-training