Aerobic and anaerobic thresholds are two fundamental values in our sport. We often hear them discussed, and they are key parameters in planning a workout.
What are they? Before discussing their mechanisms, it is best to recall what aerobic and anaerobic metabolism are, as they lie at the base of these thresholds.
The aerobic mechanism occurs in the presence of oxygen and is the most efficient, while the anaerobic mechanism causes our bodies to produce energy even in the absence of oxygen. The latter is predominant when we put in maximal or sub-maximal efforts.
Our body mainly uses two principal anaerobic mechanisms: that of oxidative phosphorylation (alactaid anaerobic) and anaerobic glycolysis (lactaid anaerobic).
We can understand the thresholds by analysing what happens when we run.
When the body begins physical activity, the first mechanism that comes into play is alactaid anaerobic, coupled with aerobic metabolism, which is less efficient in this first phase. There is therefore a slight increase in lactate in the blood.
Then the aerobic mechanism starts to step up, and creates the motive force. The lactate tends to diminish slowly, returning to rest values. Consider that when there is up to 0.8-1 mmol/l of lactate in the blood, the body works in total ease.
As the body’s effort increases, the lactaid anaerobic mechanism increases lactate production in the blood up to a value of 2mmol/l, which corresponds to the aerobic threshold. This is often referred to as the marathon rhythm because when accompanied by an appropriate training schedule, with a value of 2mmol/l of lactate in the blood, runners can cover long distances.
The value of the anaerobic threshold is instead conventionally fixed to 4mmol/l lactate in the blood. Increasing the speed beyond the aerobic threshold described above therefore also increases the level of lactate in the blood. The body reaches the point where the production of lactate increases but its speed remains constant, up to the point where the body is unable to dispose of the excess lactate and is forced to slow down or stop. The average, trained athlete can hold the anaerobic threshold level for about 40-45 minutes.
So we can define the aerobic threshold as the minimum speed at which the level of lactate remains at constant levels which are greater than rest levels. The anaerobic threshold is instead the maximum speed at which the level of lactate remains at constant and greater levels than those of rest.
The calculation of the latter threshold (anaerobic) is especially important in an athlete’s training program, because it allows the rhythms of any training medium to be planned.
By Lorenzo Andreini – Santucci Running