Analysis of Thresholds: Lactate, Ventilatory,

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Analysis of Thresholds Lactate, Ventilatory,
Heart Rate
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Determinants of endurance performance
Performance measure?
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Lactate Threshold
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What is the lactate threshold (LT)?

• Point La- production exceeds removal in blood
• La- rises in a non-linear fashion
• Rest La-? 1 mmol/L blood (max 12-15 mmol)
• LT represents ? anaerobic metabolism
• large ? glycogenolysis glycolytic metabolism
• ? recruitment of fast-twitch motor units
• mitochondrial capacity for pyruvate is exceeded
• pyruvate converted to lactate to maintain NAD
• ? Redox potential (NAD/NADH)

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Other possible causes of LT

• Ischemia muscle hypoxia
• unlikely due to muscles ability to extract O2
• Increased catecholamines in blood
• contribute to increased glycogenolysis
• One thing is for certain
• cant maintain prolonged exercise above LT!

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Review of mechanisms to explain LT
? La- production
? Blood catecholamines
Mito. Capacity for pyruvate exceeded
? Redox potential
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Measuring LT
Blood lactate has a curvilinear response with ?
exercise intensity
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Mathematical transformation
Intersection of the 2 lines is identified
as the LT!
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Training status and LT
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Lactate Threshold

• LT as a of VO2max or workload
• sedentary individual? 40-60 VO2max
• endurance-trained? gt 70 VO2max
• LT point of maximal SS- exercise
• max intensity SS-exercise can be maintained
• prescribe intensity as of LT!!

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Lactate Threshold

• Exercise intensity at LT
• best measurement for predicting performance
• middle to long distance (duration) events
• 5 K to marathon
• higher the LT, faster you can run at sustained
  pace!
• No universal guidelines for measuring LT
• Several methods for documenting a threshold
  change in blood La-

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Other Lactate Threshold terminology

• Anaerobic threshold
• first used in 1964
• based on ? blood La- being associated with
  hypoxia
• known to be an oversimplification, should not be
  used
• Onset of blood lactate accumulation (OBLA)
• maximal steady state blood lactate concentration
• can vary between 3 to 7 mmol/L
• Usually assumed to be around 4 mmol/L

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Research has shown considerable similarity in
each of the exercise intensities obtained from
the different lactate threshold methodologies
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Non-invasive methods to quantify Lactate Threshold
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Ventilatory Threshold

• More concrete guidelines for VT
• 2 methods accepted in research
• Ventilatory equivalents (VE/VO2 VE/VCO2)
• V-slope (VO2 VCO2)
• Relation of VT LT
• highly related (r .93)
• 30 second difference between thresholds

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Ventilatory Threshold

• Ventilatory equivalents
• graphed over VO2 typically!!
• Look for non-linear rise in VE/VO2
• not followed by rise in VE/VCO2
• eventually rises after VE/VO2

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Ventilatory Threshold

• During incremental exercise
• increased acidosis (H concentration)
• buffer this with bicarbonate (HCO3-)

H HCO3- ? H2CO3 ?
H2O CO2
Lung
Muscle
RBC

• Marked by increased ventilation
• hyperventilation!!

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• VE
• ? linearly
• breaks off abruptly
• due to ? acidosis (H)

VE
VE/VO2

• VEVO2
• initially ?
• ? abruptly
• exceeds ? in VO2
• VT occurs here
• VEVCO2
• initially ?
• ? abruptly 1-2 min after VT

VE/VCO2
VO2
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Heart Rate Threshold

• HR doesnt increase linearly up to VO2max in all
  people
• can lead to errors in predicting VO2max
• Point where HR-VO2 deviates from linearity
• Heart Rate Threshold (HRT)

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Heart Rate Threshold
Note the decreasing slope of HR
HRT
Note the linear portion of HR
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Training at the Lactate Threshold
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Should exercise intensity be expressed relative
to LT or VO2max?
VO2max
LT
Better way to equate a relative intensity based
on metabolic state
max SS capacity
max SS capacity

non-SS capacity
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Intensity expressed relative to LT?

• To do prolonged exercise training
• need to know LT
• To do interval training
• need to know LT
• best for improving VO2max
• For well trained individuals
• LT and VT are more sensitive indices of training
  improvement than VO2max

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LT better measure of endurance
performance!!!
What have we learned?
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Questions???
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The regeneration of NAD sustains the continued
operation of glycolysis.
If NADHH cant pass hydrogen ions to the
mitochondria Its hydrogen ions are passed to
pyruvate to form lactate! Why is this important???
The formation of lactate is crucial to cellular
metabolic function!!
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Lactate production
Oxidizing Power
Regeneration of NAD allows glycolysis to proceed!
NAD
Lactate
Pyruvate
NADHH doesnt enter mitochondria
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Why La- is the Luke Skywalker not the Darth
Vader of metabolism

• Doesnt cause the acidosis related to fatigue
• -pH in body too high for Lactic Acid to be
  formed
• Assists in regenerating NAD (oxidizing power)
• -No NAD, no glycolysis, no ATP
• Removes H when it leaves the cell
• -helps to maintain pH in muscle
• La- can be converted to glucose/glycogen in liver
• -via Cori cycle

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Other Mechanisms for the Lactate Threshold

• Failure of the mitochondrial hydrogen shuttle to
  keep pace with glycolysis
• Excess NADH in sarcoplasm favors conversion of
  pyruvate to lactate
• Type of LDH
• Enzyme that converts pyruvate to lactate LDH in
  fast-twitch fibers favors formation of lactate