Transcript Blood Lactate Accumulation and Removal

Blood Lactate Accumulation
and Removal
Effects on Blood Lactate
Concentration
Lactate Response to Prolonged Exercise
(70% of VO2max)
Lactate (mM)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
30
60
90
120
150
180
Time (min)
(Kolkhorst & Buono, Virtual Exercise Physiology Lab, 2004)
Lactate Response to Prolonged Exercise
Lactate Response to Incremental Exercise
(endurance-trained athlete)
Lactate (mM)
12
10
8
6
4
2
0
0
10
20
30
40
50
60
70
80
90
100
% of VO2max
(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?
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).
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
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