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Exercise Phys. week 5

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winniesmith2's version from 2017-10-31 20:45

Section 1

Question Answer
Why do people train with heart monitorsEasy-to-use, to know the intensity of exercise, to see which domain of exercise they are in.
What is the relative rate of ATP forms per second for phosphcreatin/ how much ATP formed per substarte10 / 1
What is the relative rate of ATP glycolysis/ ATP formed per substrate5/ 2-3
What is the relative rate of ATP for oxidation from carbohydrates/ ATP formed per substrate2.5 / 36-39* (net production 32)
What is the relative rate of ATP for oxidation from fat/ ATP formed per substrate1.5/ >100 - most energy dense, but slow
When does lactate occurIn glycolysis. Glucose turns into pyruvate. NAH+ is needed for reaction, therefore NADH is formed but lactate is produced when NAD+ is regenerated. by lactate dehydrogenese.
Why should we measure blood lactate (BLa)We can use it to predict endurance performance, indicate submaximal fitness and as a tool for exercise prescription. Once BLa exseeds a certain concentration, exercise duration becomes finite.
Why do increases in lactate concentration decreased performanceLactic acid dissociates into lactate and hydrogen ions.  environment of the cell becomes more acidic (muscle pH can fall from 7.0 to ~6.3 during high‐ intensity exercise)  Inhibition of cross‐bridge formation  Inhibition of enzyme function . (but H+ is not the only factor causing fatigue, can occur without changes in pH. Lactate itself is not toxic nor a waste product- need it for NAD+ in glycolysis and to oxidate for energy.
Lactate vs pHmore lactate the lower the pH. Correlation.
When is lactate produced / not produced • Anaerobic pathway (glycolysis) does not mean lactate is only produced in hypoxic state, as postulated in Wasserman’s ‘Anaerobic threshold theory’ (1973)!! • It is true that lack of oxygen can cause increases in glycolysis resulting in lactate production BUT: – Lactate is produced at rest (resting blood lactate levels: ~0.5-1.5 mmol/L) – Lactate is produced in fully oxygenated muscle  Hypoxia cannot independently explain lactate production!
Imbalance between rate of glycolysis and mitochondrial respiration: oxidative metabolismDespite sufficient oxygen, electrons are not transferred rapidly enough through the electron transport chain to deliver the energy required
What causes an increase in glycolysisincreased catecholamines (favour fast energy) independent of oxygen availability.
What is the function of lactate dehydrogenase (LDH) function in fast twitch (Type II) fibres favours pyruvate -> lactate
What is the function of lactate dehydrogenase in slow muscle fibres (Type I) favours lactate -> pyruvate
How does lactate dehydrogenase work in the body As with any enzyme, it balances substrates and products. Fibre recruitment during progressive exercise: Shift from Type I -> Type IIa -> Type IIx
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Section 2

Question Answer
What determines blood lactate concentrationLactate production minus lactate removal. Blood is combination of production and clearance.
What happens in athletes as well trainedHigh capacity to remove lactate
Process of lactate from muscle to liverLactate is produced in the muscle by glycolysis is removed into the blood and lactic acid moved into liver where it is used to produce glucose- the cori cycle.
Size of blood lactate removalMost is oxidised in working muscle. Liver and kidneys: 20 to 25%. Cardiac muscle- 10%.
Muscle as a consumer of lactate: lactate shuttling– Only ~50% of produced lactate appears in vascular bed -> Lactate produced by fast twitch fibres oxidised in slow twitch fibres (diffusion) – Shuttling through vasculature: Reperfusion of heart and active muscle
How could we maximise lactate removal after a sprintLow intensity exercise to get blood to the muscle. The intensity were no further lactate will be produced.
Animal study: enhanced lactate removal after endurance training. Donovan et al. What did they do • Rats • Training: 60min/day, 5 days/week, for 8 weeks • Infusion of lactate • Measurement of removal rates. control needed high concentration of lactate for net lactate to be at highest, Showed that the more trained you are the more sensitive you are to lactate removal (removed at lower concentration).
Lactate threshold versus lactate turnpointheart rate increases linear. Lactate not sloped. Lactate threshold - The first point where your lactate increases (no longer flat). Fixed reference value- not a good measure as changes for each individual so we use lactate turnpoint - individual.
Determination of lactate threshold– 0.2 mmol/L above resting concentration –OR 0.5 mmol/L above resting concentration – first significant elevation of lactate level (approximately 2 mmol/L)
Determination of lactate turnpoint – The second lactate increase of at least 0.5 mmol/L from the previous value (in a step test protocol) – Dmod: 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)
Maximum lactate steady-state (MLSS or MLaSS)• The highest blood lactate concentration that can be maintained over time without a continual blood lactate accumulation • When determining the lactate turnpoint, we really want to estimate MLSS!. To determine this measure max lactate steady state multiple times at different constant speeds, until highest speed where lactate is produced at a steady state but doesn't increase. between 2-10 mmol/L.
IMPORTANT POINTS/ MLSS The lactate turnpoint / MLSS is NOT the point where metabolism “switches” from aerobic to anaerobic! • Aerobic and anaerobic processes always occur concomitantly • 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
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Section 3

Question Answer
Low intensity domainBelow the LT; BLa < 2 mmol/L; < 70 % Vሶ O2max
Moderate domain Between the LT and the MLSS; BLa elevated but stable at 2 to 8 mmol/L; 70-90 % Vሶ O2max
Severe domainAbove the MLSS; BLa > 2-8 mmol/L; > 90 % Vሶ O2max
Lactate threshold as a predictor of endurance performance- Hagberg and Coyle (1983). Med. Sci. Sports Exerc. 15(4): 287‐289. As race pace increases V02 Max increases and velocity lactate turn/pointthreshold increases.
Lactate term point and training statusA trained person will have a higher VO two max, and velocity at lactate term point is higher (higher percentage) graph at end of PowerPoint. Maximum doesn't have to change but percentage changes.
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