Why Cyclists Train with Power?

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Why use Power?

Traditionally, the training zones that we cyclists used were based on heart rate and built using your lactate threshold. This point, also known as the anaerobic threshold, was considered to be the key factor in determining an individual’s training zones, being the point at which endurance performance will start to deteriorate as the intensity of the exercise increases and lactate production exceeds its removal.

Now power is considered to be a much more reliable measurement than heart rate for establishing your metabolic intensity or training zones. During progressive ramp testing, the heart rate curve deflection point used to indicate this lactate or anaerobic threshold, proved unreliable for certain athletes when compared with their actual lactate measurements.

Why this unreliability occurs is complex but may be primarily due to the fact that the heart rate depends on neural factors and on the autonomic nervous system. Combine this with other variables such as fatigue and training overload that may influence the maximal, submaximal and baseline heart rate, and its not a very reliable measure.

Why training zones are so important?

This graph shows the concentration of lactate in blood with an exercise intensity 10% above the anaerobic threshold (Source: Gondim FJ, 2007) and clearly demonstrates how an exercise intensity just 10% above your anaerobic threshold can lead to a high accumulation of lactate, which is associated with fatigue and limited performance.

From this you can see the importance of thresholds to control your training intensity in a more scientific manner. When the intensity of your training reaches the anaerobic threshold, your body increases the combustion of muscle glycogen to maintain this high training load, but your body’s glycogen reserves are limited and it is not possible to maintain long periods of exercise at the expense of this type of metabolism. This is one of the reasons why some cyclists train under fasting conditions; they seek to improve the aerobic threshold and thus improve the efficient and effective consumption of fat which is unlimited in supply.

Moreover, when the intensity is greater than the anaerobic threshold, metabolites begin to accumulate as a result of the combustion of glycogen in anaerobic conditions (i.e. absent of oxygen). If these metabolic residues are not re-synthesized or eliminated fast enough, they can limit the effectiveness of muscle contractions and thus the mechanical power output of the muscles.

As we can see in the graph above, an intensity greater than the anaerobic threshold will lead to a constant and progressive accumulation of lactate, which will result in lower intensity and performance.

Thus its important to know your training zones based on your aerobic and anaerobic thresholds. It allows you to train at your maximal aerobic capacity without going anaerobic which would lead to the rapid deterioration of the session.

Having said that using power to monitor training intensity may be more accurate, do not totally dismiss lactate pathways and heart rate. Heart rate monitoring still has advantages in economic and practical terms. It is easy to interpret and may also be useful to assess times of overload and overtraining, especially when combined with lactate curves and questionnaires to determine a your psychological stress. Under conditions of overtraining, you will usually see a reduction in your heart rates at both submaximal and maximum intensities, often accompanied by an increase in your baseline heart rate.

We should not forget that during training at maximal intensity, such as sprinting, the ability to generate maximum power is related to the ability to access muscle glycogen. Such repeated processes during competition, brought on by things like reacting to continuous changes in speed and cadence, increase the possibilities of involving anaerobic metabolism and promoting earlier fatigue when there is incomplete recovery between activities.

This diagram shows the type of energy consumption, with fat in red and glycogen in blue, in proportion to the intensity of the exercise (Source: Rapoport B, 2010).

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