Q - Power
Intensity (4 of 6)
We now have the bottom and top of the scale established. So how do we go about slicing the scale up into bands. After all, everyone is always talking about which training “band” they should be in. To understand the significance of these bands, we need to go back to the car example.
On the road there are clear bands at 30mph, 40mph, 50mph, 60mph and 70mph. These speed limits are there because someone has put them there, but the car itself does not know they are there. In fact they are utterly irrelevant as far as the car is concerned. The car might be interested in a speed of 37mph, for example, because it happens to be the speed at which the automatic gearbox will change from 3rd to 4th gear on the flat – that is relevant to the car. The bands are not.
So we might create a band at 75%VO2max, but are we not doing that because it is a nice round number? Are there any points on our scale which are actually significant to the exercising body – points at which something changes in the way our engine is working? The answer is yes: there are two of them.
In order to see them in action, we need to start at idle and slowly push the throttles forward, watching carefully what happens as we do. As the intensity starts to build through 10%HRR from getting out of bed (HR50), 20% moving around the house (HR66) to 30% at a gentle walk (HR82) we see an increase in ventilation ("VE", i.e. the amount of air being breathed in and out per minute), O2 consumption and CO2 production. All three parameters increase in proportion to one another and blood lactate concentrations do not increase beyond resting levels.
However there comes a point at which a change occurs. In James this happens to occur at about HR151. At this intensity slightly more lactic acid starts to be produced as the muscle cells come under greater load. It is not enormous, but it is a significant change. The additional acid finds its way into the blood where it is buffered by bicarbonate. The buffering means that blood acidity does not change since the acidity is neutralised, but the buffering effect is the same as dropping Alka-Seltzer into water – carbon dioxide is given off. The numbing of physical discomfort provided by Alka-Seltzer is sadly not achieved.
What we find is that ventilation increases disproportionately to the amount of oxygen taken up as the increasing levels of carbon dioxide drive the ventilatory response. Accordingly we see an inflection point in VE/VO2 which is quite apparent in Diagram 6 below (where the blue line of best fit significantly changes gradient). Carbon dioxide remain proportionate to ventilation (the black line is not changing gradient at that point), so there is therefore an inflection in the VCO2/VO2 line as well (although VCO2/VO2 is not drawn in Diagram 6).
This point is known as the “first ventilatory threshold” or “VT1”. It is also known as the “aerobic threshold”. (Confusingly, in 1964 when Wasserman and McIlroy identified this point and described it as “the strength intensity anterior to the exponential increase factor of the blood lactate compared to the resting levels”, they decided to call it “Anaerobic Threshold”, presumably because of the beginnings of an increase in the anaerobic component).
This first threshold has also been defined as the point at which blood lactate concentrations reach 2mmol/l. This concept of fixed concentration definitions of the thresholds is one we will come back to when we look at the 4mmol/l level, but suffice it to say that it is perhaps a little outdated and of questionable benefit.
It is important to appreciate that whereas VT1 occurred in the example athlete at 75%HRR (HR151), this does not mean it will be the same for everyone. In the wholly untrained (leaving aside the fact that power output at any given percentage will be massively lower), VT1 will occur at a lower percentage of HRR. In the very highly trained, it will occur higher. Genetics will also have its part to play. It is also very important to remember that as you yourself train, it will move upwards. Stop training, and it will drift downwards.
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