HB200201

1
Anaerobic threshold concept

• HB200/201
• Functional physiology of sport and exercise

• Measures of the anaerobic threshold
• Athletic and functional significance of the
  anaerobic threshold
• Production of lactate
• Mechanisms of the lactate threshold
• Ventilatory threshold
• Maximal lactate steady state (MLSS) and onset of
  blood lactate accumulation (OBLA)
• Domains of exercise intensity

2
Various names given to the anaerobic threshold
concept

• Anaerobic threshold (AT)
• Lactate threshold (Tlac)
• Ventilatory threshold (Tvent)
• Respiratory compensation point
• Onset of blood lactate accumulation (OBLA)
• Onset of plasma lactate accumulation (OPLA)
• Individual anaerobic threshold (IAT)
• Lactate turnpoint
• Lactate minimum
• Aerobic threshold (AeT)
• Maximal lactate steady state (MLSS)
• Delta 1 mM
• RER crossover
• Much confusion over terminology

3
The functional significance of the lactate
threshold (Tlac)
4
The functional significance of the lactate
threshold (Tlac)

• Whilst a high VO2 max is a prerequisite for
  success in endurance events
• The ability to sustain a high of VO2 max
  without accumulating fatigue is of greater
  importance
• Radcliffe 91 VO2 max for half marathon (64
  ml/kg/min and 19.0 km/h)
• Tlac is a functional index of muscle metabolism
• Lactate inhibits lipolysis (utilisation of fat)
• Accelerated glycogen utilisation above Tlac
• Well-trained marathon runners operate just above
  Tlac
• Tlac is a functional index of muscle fatigue
• High levels of H interfere with
• enzyme activity
• cross-bridge attachments

5
Lactate threshold even influences high-intensity
performanceCase study Jones, A. M. (1998). A
five year physiological case study of an Olympic
runner. Brit. J. Sports Med.32 39-43
6
The functional significance of the lactate
threshold (Tlac)

• Research suggests blood lactate response to
  training adapts to a greater degree than does VO2
  max
• Tlac as VO2 max
• Untrained 45 to 60 VO2 max
• Trained 60 to 80 VO2 max

7
The functional significance of the lactate
threshold (Tlac)

• Identifying the Tlac is importance to endurance
  athletes
• Sets the highest work-rate that can be sustained
  without fatigue or rapid glycogen depletion
• Useful for setting upper limit of aerobic or
  steady training

HR at Tlac 152 bpm
Tlac
8
Metabolic factors influencing lactate production
9
Metabolic factors influencing lactate production

• Inadequate rate of O2 delivery (hypoxia) due to
• lowered blood O2 content
• Lowered blood flow
• Imbalance between rates of glycolysis and
  mitochondrial respiration
• Increased NADH relative to NAD (decreased redox
  potential)
• ? catecholamines
• ? intensity ? adrenaline/noadrenaline
  (epinephrine)
• ? gylcolysis

10
Imbalance between rates of glycolysis and
mitochondrial respiration

• Hydrogen release in glycolysis
• Glycolysis requires NAD to strip the H atom
  from 3-phophoglyceradehyde
• H are passed to NAD to from NADH
• NADH transports H to electron transport chain
  where they are used to re-synthesise ATP

11
Imbalance between rates of glycolysis and
mitochondrial respiration

• Problem
• At high rates of energy production, the
  production of H atoms in glycolysis exceeds
  their rate of processing in the electron
  transport chain
• Limiting factor The rate of H utilisation by
  the ETC is ultimately governed by the rate of O2
  supply
• If O2 cannot be supplied at a fast enough rate, a
  backlog of H accumulates
• NADH cannot release H to ETC and thus
  accumulates
• Continuation of glycolysis can only occur if NAD
  is available to strip the H atom from
  3-phophoglyceradehyde
• Gylcolysis grinds to a halt

12
Imbalance between rates of glycolysis and
mitochondrial respiration

• Solution
• Pyruvate can provide a temporary sink to accept
  the H atoms and thus free up NADH back to NAD
• Glycolysis can continue
• Pyruvate combines with H to form lactate
• Rate limiting enzyme Lactate dehydrogenase
  (LDH)
• LDH exists in different isoenzymes
• Muscle type LDH converts pyruvate to lactate
• Heart type LDH converts lactate to pyruvate

The real reason for lactate formation to allow
glycolysis to continue
13
Mechanistic basis of lactate threshold response
14
Blood lactate threshold response

• Lactate threshold
• The first sudden and sustained increased in
  blood lactate above the near-resting
  concentrations (Wasserman et al., 1973)

15
Lactate

• Lactate is measured as a concentration La in
  the blood
• Units of millimoles (mM) (or mmol ? L-1)
• Blood La

16
Mechanistic basis of blood lactate threshold
response

• Blood Tlac mirrors muscle Tlac response
• Muscle NADH increases disproportionately to
  muscle NAD concentration above Tlac

17
Mechanistic basis of blood lactate threshold
response

• Net lactate response measured in the blood
  represents balance between appearance
  (production) and disappearance (oxidation)
• Blood lactate threshold occurs when appearance
  rate gt disappearance rate
• Appearance
• Production by muscle fibres (glycolytic fibres
  I.e. type IIX) with high affinity to produce
  lactate
• Release by muscle fibre
• Disappearance
• Oxidation by neighbouring muscle fibres
  (oxidative/type I fibres) with high affinity to
  consume lactate
• Also oxidation in Liver (Cori cycle) and heart

18
Factors that influence the production and
oxidation of lactate

• How does endurance training help raise the
  lactate threshold?
• Increased delivery of O2
• ? SV ? cardiac output
• ? Capillarisation
• Increased utilisation of O2
• ? Mitochondrial volume and enzyme content
• ? Capillarisation
• 1 2 lower necessity for anaerobic glycolysis
  at a given workload
• lower lactate production
• Increased oxidation of lactate
• ? LDH heart type LDH muscle type
• ? Capillarisation
• ? lactate transporters
• Lower production increased oxidation lower
  blood La

19
Capillarisation and enzyme changes induced by
chronic muscle stimulation and training
20
Influence of fibre type properties on lactate
production and oxidation

• Type I fibres
• High O2 delivery
• Good capilarisation
• High O2 utilisation
• High mitochondrial content
• High Krebs cycle enzyme activity (SDH/CS)
• High electron transport enzyme activity (CoX)
• Low glycolytic activity
• Low glycolytic enzyme activity (PFK)
• High activity of heart type LDH
• Readily converts lactate to pyruvate
• High concentration of transporters accepting
  lactate into cell
• Low affinity to producing lactate but high
  affinity for consuming lactate

• Type IIX (IIB) fibres
• Relatively low O2 delivery
• Poor capilarisation
• Low O2 utilisation
• Low mitochondrial content
• Low oxidative enzyme activity
• High glycolytic activity
• High PFK activity
• High activity of muscle type LDH
• Readily converts pyruvate to lactate
• High concentration of transporters releasing
  lactate from cell
• High affinity to producing and releasing lactate

21
Mechanistic basis of ventilatory threshold
response
22
(No Transcript)
23
Ventilatory threshold

• Definition Exercise intensity at which pulmonary
  ventilation (VE) increases disproportionately in
  relation to oxygen uptake during incremental
  exercise
• Where does this excess ventilation originate?

24
Ventilatory threshold

• Theory
• Lactic acid is quickly buffered by sodium
  bicarbonate in the blood (NaHCO3) to form sodium
  lactate (Na Lactate)
• Excess, non-metabolic CO2 is formed
• VCO2 disproportionately increases
• VE disproportionately increases to exhale excess
  VCO2

Lactic acid NaHCO3 ? Na Lactate
H2CO3 ??
H2O CO2
25
Mechanistic basis of ventilatory threshold
Inadequate O2 delivery
Utilisation of glycolytic fibres
? Anaerobic glycolysis
? Lactate production
Buffering ? HCO3- ? VCO2 ? RER

• Increase in minute ventilation (VE) relative to
  VO2
• Non-linear increase VE
• Increase in VE/VO2
• Non-linear increase in VCO2

26
Question

• In what ways is the terms lactate threshold
  biochemically more precise than the term
  anaerobic threshold?
• Ultimately, lactate production at the muscle
  reflects anaerobic glycolysis
• However, the observation of an increased lactate
  concentration in the blood is a complex balance
  of lactate production and removal, not just
  anaerobic conditions
• Lactate production occurs readily in fast-twitch
  fibres even though O2 supply might not be
  limiting

27
Maximal lactate steady state and onset of blood
lactate accumulation
28
Maximal lactate steady state (MLSS)

• In constant-load exercise individuals can
  actually sustain an intensity higher than the
  Tlac, at which blood La is greater than at rest
  but not increasing over time
• The highest intensity that can be sustained where
  there is a balance between lactate production and
  its removal from the blood is known as the
  maximal lactate steady state (MLSS) (Heck et al
  1985)

29
Maximal lactate steady state (MLSS)

• Power/running speed at MLSS is highly related to
  pace in events lasting 60 min
• Gold standard criterion measure of sub-maximal
  endurance capacity
• Measured in constant-load exercise (as opposed to
  incremental for Tlac)
• Requires 3 or more 30 min runs
• La measured every 5 min
• Criteria No more than 1 mM increase from minutes
  10 to 30
• Problem time consuming

Of all measures of aerobic fitness, the velocity
at MLSS has the highest predictive power of
endurance performance (Jones and Doust, 1998
Jones and Carter, 2000)
30
Power output in 1 hr cycling is highly related to
the Tlac and MLSSCoyle et al., 1991
31
Onset of blood lactate accumulation (OBLA)

• The average blood La at the MLSS is typically
  close to 4 mM (Heck et al 1985 Jones and Doust
  1998)
• Threshold value of 4 mM established from an
  incremental test as being the intensity for the
  onset of blood lactate accumulation (OBLA)
  (Sjodin and Jacobs, 1981).
• OBLA Estimate of MLSS from incremental test
• Also related to endurance performance (Sjodin et
  al., 1982)

OBLA
TLac
32
Onset of blood lactate accumulation (OBLA)

• Major problems with OBLA
• Individual blood La can be as low as 2 mM and
  as high as 7 mM
• Diet influenced
• 4 mM can severely under- or over-estimate true
  MLSS
• OBLA conclusion physiologically invalid for an
  individual, even if related to performance across
  a group

33
Domains of (submaximal) exercise intensity
34
Domains of (submaximal) exercise intensity

• Moderate below LT
• Heavy between LT and MLSS
• Severe above MLSS but below VO2 max
• Above VO2 max supramaximal

35
The blood lactate to constant-load exercise at
different work intensities.
Severe
Heavy
Moderate
36
Domains of (submaximal) exercise intensity

• Moderate below LT
• Upper limit 70 VO2 max
• Time to exhaustion 3 hours
• LT pace can be held for 3 hours (slightly
  slower than elite marathon pace)
• Blood La, H and pH at resting levels and
  stable
• Heavy between LT and MLSS
• Upper limit 85 VO2 max
• Can be held for 1 to 2 hours
• MLSS pace can be held for 1 hour
  (half-marathon/10 mile)
• Blood La and H above resting levels (pH lower)
  but maintained at stable level after initial
  adjustment ( 10 min)
• Severe above MLSS but below VO2 max
• 5 to 60 min
• VO2 max pace can be held for 4 to 8 min pace
  (3000 m)
• Blood La and H well-above resting levels and
  increasing over time (pH lower than resting and
  decreasing over time)
• Above VO2 max supramaximal

37
Task

• You are a physiologist working with marathon
  runners
• In one or two sentences, describe the lactate
  threshold phenomenon in a language appropriate to
  these athletes
• What it is
• What are the primary factors that cause it
• Why its important to them

38
Main points

• Blood lactate is produced when anaerobic
  glycolysis outpaces mitochondrial respiration
• The Tlac occurs when lactate production is
  greater than lactate removal within the muscle
  fibres
• The mechanisms of the Tlac, Tvent and MLSS are
  complex, but their functional significance to an
  endurance athlete is important
• Training raises the Tlac and MLSS by increasing
  O2 delivery and utilisation and mechanisms of
  lactate oxidation, thus off-setting anaerobic
  glycolysis and increasing lactate clearance
• OBLA is a poor (invalid) estimate of the MLSS
• The Tlac, MLSS and VO2 max set the upper limits
  for moderate, heavy and severe intensity exercise