Lactate and OBLA Objectives: Define OBLA and lactate Describe what happens to lactate after exercise has finished Describe factors affecting OBLA and how OBLA can be changed with training.

Lactic Acid What do you already know about lactic acid/ lactate? VO2 max testing- direct gas analysis

What is Lactic Acid? Product of anaerobic glycolysis Produced when there is not enough oxygen present to oxidise pyruvate in Krebs Cycle and ETC (in Mitochondria). What is Lactate? Lactic acid needs to be removed from the muscles Is converted into Lactate + H+ ions – lactate can be transported by the blood (Lactic Acid can’t) Resting blood lactate levels are ~ 2 mmol/L but during exercise this can increase to ~30 mmol/L

What effect does the formation of Lactate have on the muscles? Why? When lactate is formed, H+ ions are released These decrease muscle pH causing acidosis This causes fatigue (at around pH 6.4) by stopping the enzymes of glycolysis from working Also interferes with neural transmission. Why are Sports Scientists interested in measuring blood lactate levels? Muscle H+ levels are hard to measure Blood lactate levels are easy to measure, and are directly linked to muscle H+ Therefore, knowing blood lactate levels means you can tell what muscle H+ levels are, and when fatigue will occur.

Lactate threshold and OBLA Testing for Lactate threshold and OBLA

OBLA - Onset of Blood Lactate Accumulation OBLA is the point at which lactate begins to accumulate in the blood This is said to occur when blood lactate levels reach 4mmol/litre It is used to predict endurance capacities as the longer an athlete can delay the build-up of lactate, the longer they can continue exercising OBLA is usually measured by performing a test of increasing intensity, starting at an intensity of ~50% VO2max. Blood samples are taken as the intensity increased, and blood lactate levels recorded.

VO2max and OBLA VO2 max is… …the max amount of oxygen that can be taken in, transported and consumed by the working muscles per minute

Recap: At sub-max intensities (1 - 4), the amount of oxygen being supplied meets demand, so the VO2 reaches a steady level At high intensities (5 and 6), the athlete reaches a point where they cannot supply any more O2 – their VO2 max. Any energy needed beyond this point is supplied anaerobically, causing lactic acid to accumulate.

If lactic acid accumulates (OBLA is reached) before VO2 max is reached, then the body will fatigue earlier, and exercise is less efficient. OBLA can be measured as a percentage of VO2 max to show how efficient the athlete is at using his aerobic capacity. VO2 max can only increase by 10-20% as a result of training. OBLA however can be greatly increased through training. Thus performing the correct training and delaying OBLA can greatly improve aerobic performance, as the athlete can continue to exercise aerobically until VO2 max is reached

Untrained individuals usually have a OBLA of 55-60% VO2max. Trained athletes often have a OBLA of 70% VO2max or higher – Lance Armstrong for example has an OBLA of 90% VO2max!

Using your text book find out what the factors affecting the rate of LA accumulation are

Factors affecting rate of LA accumulation: Exercise intensity – higher intensity means less likely to be performed aerobically and more likely LA produced Muscle fibre type recruited – Type I Slow Twitch fibres produce less LA at the same intensity as fast twitch fibres due to more Mitochondria Rate of blood lactate removal – if removal and production are roughly equal, then blood lactate concentrations should stay constant. Only when production exceeds removal will levels rise Type of fuel being used – R:E:R – the close the value is to 1, the more glycogen is being used and the more likely LA is to be produced. Training status of muscles – if muscles are trained they will have adaptive responses including more mitochondria; greater capillary density; improved used of FFAs as fuel; and higher myoglobin content, all increasing aerobic capacity of muscle and reducing LA production.

So… we can say that: Trained athletes delay the lactate threshold (point of OBLA) or… In trained athletes OBLA occurs at a higher % of their VO2 max. This is because they are adapted to: maximise aerobic respiration – more mitochondria, capillary density, myoglobin, better utilisation of TGs etc, therefore producing less LA remove any LA produced more quickly buffer the accumulation of H+ ions This means they can exercise for longer / at higher intensities without fatiguing

What happens to the lactate? Lactic acid, or lactate, can only be removed from the body when there is sufficient oxygen to do so. This means that it cannot happen until exercise intensity is reduced, or exercise has ceased. Then the following things happen: Most (65%) is converted into pyruvate and then oxidised into carbon dioxide and water through aerobic respiration in inactive tissues, producing ATP Some (20%) is converted into glycogen in the liver Some (10%) is converted into protein Some is converted into glucose Some is excreted in sweat and urine. This takes up to 1 hour, and is faster with an active cool down period

Check your understanding of OBLA Complete task 1.14 from page 24

Exam Question

Answers 1a) 1 Lactate threshold correctly identified as 500 - 800 Watts 2 Lactate from anaerobic (glycolysis)/ lack of O2/high demand lack of supply 3 High intensity/ workload/ equivalent 3 b) 1 Used as respiratory substrate/ for respiration/ energy/ using oxygen/ lactate to replenish ATP 2 Converted to pyruvate 3 then to carbon dioxide and water 4 in inactive muscles and various tissues/ organs 5 Converted to glycogen/ glucose 6 In liver 7 Some excreted in sweat/ urine/ conversion to protein 4