Lactate threshold and ventilatory threshold

The Lactate Threshold

I read an article on the peak performance website that explains how increased lactate threshold will improve peak performance (Anderson,n.d)

I learned that Glycolysis is the production of energy from glucose. Glucose is broken down into Pyruvic acid. Pyruvic acid is then used in the krebs cycle to creates over 90% of the energy you need to run. During strenuous exercise there can be  a large accumulation of Pyruvic acid within the muscle cells.

Ok so what?

Well this large accumulation of Pyruvic acid  (pyruvate) makes a change in the normal steady state a body can function in. An enzyme (an effector) is then activated that breaks down and converts this Pyruvic acid into lactic acid (lactate).

I’ve always heard that the burning in your muscles is what they call the lactic acid build up.

Apparently not!

Lactic acid (lactate) is used to metabolise carbohydrate (CHO). When CHO is metabolised one of it's by products is Carbon dioxide and water.

Lactate is also used by the muscle to create glycogen which provides energy we store for later (wow didn’t know that). The lactate shuttle explains how pyruvate is converted to lactic acid, Lactic acid then escapes (no blocking the production of Pyruvate from Glucose) into other muscle cells where it has two uses. Firstly, it can be broken down to form ATP, or it can be used as a building block to form glycogen to be stored.

The article explains when you first start exercising your lactate levels rise as the demand for more energy is increasing. When you start exercising initially your breathing and heart rate is low which is not supplying enough oxygen. Oxygen is used to break down Pyruvate. So while yo are getting warmed up there will be a build-up of lactate in your muscles.

As your breathing rate and heart rate increase, more oxygen is delivered and more lactate is converted to energy and that’s why after some time exercising that second wind comes into effect.

However if you were to increase the amount of work within a training session to a certain point this would produce an imbalance between the lactate production (through conversion of Pyruvate) and the muscles ability to convert (or clear) the lactate from the blood. This is most likely because the muscles cannot convert all the lactate being formed so this excess builds up in the blood stream. This is called Lactic acidosis…which causes a drop in the PH of the blood which makes it more acidic-  I bet that signals an integrating centre somewhere to effect a change!

So how do we increase this lactate threshold?

Andrews states that intense training is the best LT booster, because activities that are closer to maximal capacity improves the heart's capacity to deliver oxygen, the muscles' ability to use oxygen once it's delivered, as well as the ability of the heart and muscles to 'clear' lactate from the blood.

Keith, Jacobs and McLellan (1992) did several tests involving runners training below LT, at LT and above LT. The results showed that training at LT and above provided the greatest gains however the group that trained above LT could maintain the  same amount of work for longer – This result shows quite clearly the application to increase adaptation for endurance sports

From this information, In order to increase my football boys overall aerobic capacity and increase their lactate thresholds I will be adding some intense interval training activities (15min each) within training sessions as not only does adaptation occur when one works above the lactate threshold as opposed to below it but short bursts working at these levels provides the same adaptation rates as longer durations at the lactate threshold or below.

What do I need to understand more about?

What happens when the PH of the blood drops in the blood stream and what are the responses?? 

 

 The Ventilatory Threshold

A test we completed was a graded exercise test where a participant on a tread mill was exposed to increasing loads whilst measuring heart rate and breathing rate through specialised equipment. There is a principle that during a submaximal test, heart rate and breathing rate increase in a linear fashion as work increases. So the more distance a runner runs and the faster they run the more work they are doing (Work + force x distance. This was evident for most of the test until a certain point where the gradient sharply increased. So what?

McArdle et al. (2010) explain this phenomenon as reaching a “ventilatory threshold”. They state that that ventilatory threshold is the point in which ventilation increases disproportionally with O₂ consumption. With sub maximal tests a straight line occurs. However the change in respiratory frequency could indicate a maximal level of exercise has been reached.

So what do I not understand?

Why does ventilation increase disproportionately with O₂ consumption?

When we did some submaximal and maximal tests in a lab to measure VO_2max. I know that cardio respiratory tests indicate fitness levels through measuring or estimating your VO_2max. And it was quiet interesting when you see a VO_2max test in action. You could see that when the workload increased so did respiration and heart rate in a linear fashion. Fick’s Equation explains that VO_2max is equal to cardiac output (Q) multiplied by the difference in the arterial (ā) and venous (ṽ) O₂ content of the blood.

VO_2max = Q x (ā - ṽ diff).

So what is cardiac output?

Cardiac output is how much blood your heart can pump in a minute and is described as the stoke volume (that’s how much volume of blood your ventricles can pump per contraction) multiplied by how many contractions within that minute. I would relate this to being similar how much gas a petrol pump could pump out in one minute.

What I found interesting was when the work load increased to a certain point there was a change in the breathing rate gradient which became much steeper. I know that VO2 max is the maximum uptake of O₂ by the body and this is normally tested in a submaximal test where the data is been extrapolated In order to predict VO_2max. At certain point in the graded exercise test (where work was increased in incriments over time) breathing rate showed a sharp increase in gradient and no longer travelled in a linear fashion even when the increased workload stayed the same.

So why does breathing rate suddenly change gradient when the workload is increased over a certain point?

This was explained to me as a ventilatory threshold (V_T). OK so what is that exactly?

McArdle, Katch and Katch (2010) explain in chapter 14 that ventilatory threshold “describes the point where pulmonary ventilation increases disproportionately with O₂ consumption”.  Apparently this means that the breathing rate is no longer tied to the amount of O₂ our muscles demand but the build-up of CO₂ within the blood stream through the glycolysis process (anaerobic process). Ok so I understand that breathing is in fact driven by CO₂ removal. 

So how is this CO₂ produced?

Glycolysis is a process whereby energy is created using glucose in the blood. This glycolysis process creates lactate. As we exercise and increase our work rate, more lactate is produced. The body’s homeostatic receptor mechanisms detect this change in PH within the blood. This causes a buffer to be produced which is called sodium bicarbonate (this is homeostatic effector mechanism!). This reaction between lactate and sodium bicarbonate causes CO₂ and water (H₂O) to be produced. Normally the rate of lactate removal is equal to the rate it is being produced even at high concentrations of lactate production. When work load increases Our Heart rate increases to deliver more blood to the lungs in order to remove the waste (CO₂). If this build-up of CO₂ is beyond our capacity to remove it through our lungs, the response is to increase breathing rates. If by doing this the PH is still within unacceptable limits our breathing rate will increase further. This is why our lungs are the limiting factor on our performance! In application, looking after your lungs would be paramount for any athlete.

This is the main reason why promoting being “smoke free” to our athletes is so important. If we reduce our capacity to remove CO₂ we reduce our ability to perform.

So if I were to explain this to students:

As we perform more work our heart rate and breathing rate increase in a straight line. When work increases to a point where our breathing rate increases disproportionately this is the “ventilatory threshold”.

The lactic threshold is caused by a build up of carbon dioxide fromin the blood due to not enough oxygen being supplied to break this Lactate down to energy. This causes a drop in PH within the blood. This increased acidity drives the needs to expel more CO2

As the work rate of our muscles increases, the CO2 produced by the muscles increases also. This increased CO₂ within our blood makes the blood more acidic (lower PH). Detection of increased acid in the blood causes the heart to beat faster. This delivers more blood to the lungs to expel this waste in order reduce the acid levels in the blood.

At this point the heart is delivering blood at a rate that matches the work. Fick’s Law of diffusion states the rate of gas exchange across tissues is dependant on tissue area, membrane thickness, gas co-efficiency and the difference in partial pressure of the gas between the blood and the atmosphere. If our lungs can’t diffuse enough CO2 across the alveolar membrane per expiration, the response is to increase the breathing rate.

You will feel as if this is a desire for more air – gasping for breath when you have done a really intense run.