4 - Blood Lactate

Summary of Bla

1. Glycolysis

• Carbs - 2x ATP

• Fat - 3x ATP

2. Lactate - not independently produced in hypoxia (depends on rate of energy demand)

3. Lactate reflective of fatigue mechanisms

• H+ causes decrease in: pH, ADP, Pi

• Reflects elevated glycogen utilisation/depletion

Hypoxia

When the body’s tissues are deprived of adequate o2

BLa as ‘GOOD’

1. Exercise for longer - extra supply to be oxidised and fuel

2. Lactate conversion produces NAD - glycolysis to continue

3. Acts as a buffer

BLa as ‘BAD’

1. Increases acidic byproducts

2. (lactate itself not awful, but the acidosis alongside it)

Acidosis

too much acid in the body’s fluids causing a low pH

Lactate

Produced when cells break down glucose for energy (base of lactic acid)

1. Only measurable thing, not lactic acid

2. Can be an energy source - transported to liver and, converted back to glucose

Traditional view of Acidosis in High Intensity Exercise

• Glucose has 6 Carbon molecules — split in 3 (pyruvate) (end of anaerobic portion of glycolysis)

1. Low enough rate for an oxidative process

• Pyruvate becomes acetyl coenzyme A

• Goes into Krebbs cycle 

2. High enough rate (no O2)

• Pyruvate becomes lactate (Fermentation)

3. End of Pyruvate conversion - LDH (Lactate Dehydrogenase)

• Enzyme that manages reversible reaction between lactate and pyruvate

4. End result = H+ , Lactate produced

• X Increases acidity

Recent View of Acidosis in High Intensity Exercise - Lactate Prevents Greater Levels of Acidosis?

Robergs, Ghiasvand and Parker, 2004

• LDH results in immediate lactate production

1. LDH does conversion which is reversible

2. Lactate can go back to pyruvate

3. Recycling of NADH to NAD

4. Only measurable thing is lactate

5. If this is true, some hydrogen ions are being consumed which helps to buffer acidity levels to slow conversion of lactate stopping acidosis (LACTATE BENEFICIAL)

Lactate and pH

First Graph

1. Direct relationship between BLa and pH

2. Things that give away Hydrogen are acid

3. More acidic, Higher BLa concentration, Lower pH

Second Graph

1. Measured P’s BLa - can assume acidosis is occuring

2. Process by which we clear lactate from body also consumes H+ - brings pH back up

What Determines Blood Lactate Concentration

1. At rest BLa = 1-1.5 mmol per litre

2. Liver > Cori cycle > Turn lactate into glucose to be stored 

3. Lactate metabolised in brain tissue - protect

Lactate Production and Removal

1. Light intensity - some lactate produced, most cleared

2. Higher intensity - more lactate, more build up

3. High intensity - rate of clearence can't keep up so lactate builds up

Sites of BLa Removal

1. Most oxidised in working muscles

2. Liver/Kidney = 20-25% (cori cycle produces new molecules of glucose)

3. Cardiac muscle = 10% (oxidised)

Muscle as a Consumer of Lactate

Lactate shuttling

1. Only 50% of produced lactate appears in vascular bed

2. Lactate produced by fast twitch fibres oxidised in slow twitch fibres (diffusion) 

3. Shuttling through vasculature: Reperfusion of heart and active muscle

1. Lactate produced in T2 fibres

2. Shuttled to adjacent T1 fibres in same muscle

3. Gets utilised as a fuel source so never makes it into blood

1. Lag = lactate that does make it into blood takes time (lactate still increases after stopping maximal exercise)

Lactate as a Fuel

• As such, moving the lactate within the muscle fibre and utilising is beneficial

• Moving to other muscles working aerobically (or not involved in the exercise) is beneficial

• Moving to liver for gluconeogenesis may be beneficial

Lactate isn’t a Waste Product : Cori Cycle

1. Gluconeogenesis in liver

Glucogenesis

Creating new glucose

Why Measure in BLa

1. How much T2 have contributed

2. Predict endurance performance

• Indicate submaximal fitness - exercise prescription, monitoring, training intensity

3. BLa exceeds certain con in steady state = exercise duration becomes finite

4. Change in pH becomes problematic

• Low pH limits pfk - stops glycolysis

5. High BLa = working through glucose stores at high rate

Determination of Lactate Thresholds

25 different thresholds

Lactate Thresholds

1. 0.2 mmol/L above resting concentration

2. 0.5 mmol/L above resting concentration

3. first significant elevation of lactate level (approximately 2 mmol/L)

Lactate Turnpoint

1. The second lactate increase of at least 0.5 mmol/L from the previous value (in a step test protocol)

2. D mod : Maximal distance from BLa curve to the line formed by the point before the first rise in BLa and the value at cessation of exercise (see lab book for details)

Lactate Threshold

the point during exercise at which the body starts producing more Lactate than it can clear — so lactate (and associated hydrogen ions) begin to accumulate in the blood

Lactate Turnpoint

a point during increasing exercise intensity where blood lactate concentration begins to rise suddenly and steeply, meaning the body is producing lactate faster than it can clear it.

Determination of Lactate Thresholds

1. Dmod

2. Draw a line from where lactate starts to increase to the maximal point

3. Max distance between that line and curve is 2nd threshold

Lactate Threshold vs Lactate Turnpoint

1. Low level intensity - lactate is stable and near baseline

Maximum Lactate Steady State (MLSS/MLaSS)

The highest blood lactate concentration that can be maintained over time without a continual blood lactate accumulation (the highest speed that can be maintained with lactate levels at a constant state)

1. If we go above lactate turnpoint, even if we stop increasing intensity, lactate doesn't achieve steady state, it keeps climbing

2. Determine lactate turnpoint, we estimate MLSS (estimate lactate steady state)

3. Can be done in 1 test (Incremental step test)

Determining MLSS

1. Perform steady state at each different intensity (speeds)

2. All eventually reach steady state until highest intensity

Important Points

1. Lactate Turnpoint/MLSS is NOT the point where metabolism ‘switches’ aerobic to anaerobic

2. Aerobic + Anaerobic always occur concomitantly (even at low some anaerobic)

3. At intensities higher than the lactate turnpoint / MLSS, anaerobic processes lead to a gradual build-up of H + and other metabolic products in muscle, ultimately leading to fatigue

Training Zones : Exercise Domains

1. Low intensity 

2. Moderate 

3. Severe (Domain)

Low Intensity Domain

Below the LT:

BLa < ~2 mmol/L;

< ~ 70 % O2max

Moderate Domain

Between the LT and MLSS

BLa elevated but stable at ~2 to 8 mmol/L;

~ 70-90 % O2max

Severe Domain (Interval)

Above the MLSS

BLa > ~2-8 mmol/L;

> ~ 90 % O2max

Lactate threshold as a predictor of endurance performance: 20-km race walking

1. A

• Strong positive

• BLa better indicator than VO2 Max

1. Adaptations can shift curve to right

2. Thresholds occur at higher intensities

3. Can work harder

Lactate turnpoint and training status

Using the lactate threshold to evaluate the effectiveness of an endurance training programme

1. Curve shifts to the right

2. Lactate curve moves with threshold

Summary