TRAINING WITH A POWER METER?
5 months ago
Training with power and the use of power meters have become increasingly popular. Recent price drops in power meters, and the advent of cost effective power meter’s for mountain bikes has caused a big increase in the number of power meters seen on our local trails and in local races. Previously, you would have had to ride with a wheel with a built-in power meter hub, or buy an expensive crank based power meter. Now for only around R10 000 you can match virtually any MTB crank with a power meter containing a crank arm.
What is the benefit of a power meter?
I have learnt from my experience that the majority of the market, be it novice cyclist or professional cyclist, doesn’t truly understand the benefits of a power meter, and often doesn’t know how to use a power meter correctly during training. The true benefit of power meters is not fully understood. If you had to ask one of your friends who had just purchased a power meter what the benefit is, their response would probably be down the lines of being able to ‘train to power” or to “perform power training”. These statements imply that a power meter is going to result in them training very differently, and that this training would not be achievable without a power meter. The truth is that a power meter is not, and should not change the way you train. Cyclists have been training and pushing themselves for decades. Professional cyclists aren’t suddenly training differently because they have power meters. The true benefit of a power meter is the ability to objectively quantify your performance, and to quantify your total workload during a specific training session or race.
Certain individuals may not agree with me that a power meter does not change the way you train. They may say that you are able to train and remain in a specific power zone (power output) for a determined duration. There is however little evidence supporting that training in this way is more accurate than simply riding to feel (perceived exertion) or heart rate. Dr Jeroen Swart and colleagues from the University of Cape Town performed a very interesting research study, which was published in the Journal of Strength and Conditioning Research. In this study they compared intervals performed at a specific power output, and compared this to intervals performed to a heart rate equivalent intensity. Most interesting was the notable difference of how intervals were performed. Compared to the power groups that performed constant power efforts, the heart rate group started off much harder to get their heart rate up, followed by a gradual drop in power while maintaining a constant heart rate. The interval average power was identical between the two groups. When the responses to these intervals were compared, the study demonstrated a tendency for the heart rate group to improve more than the power group. This indicates that there is no rationale for advocating intervals to a specific power. The reason for the greater adaptation in the heart rate group may have been due to the high power at the start of the interval. This just simply illustrates that the primary benefit of a power meter is not, as many advocate, to perform training at a certain power. The true benefit of a power meter, in my opinion, is to receive objective feedback and monitor progression.
How to use training data to ensure progression?
This leaves us with the question how should we be analysing our data to ensure that we are improving? Commonly, hard training sessions consist of interval sessions. The major advantage of training with a power meter is that it provides you with an exact objective measure of your performance. There is little benefit in simply looking at your average power across a ride, you should search deeper. You should analyse and plot each interval and calculate your “session average” for the specific sessions. Therefore if you do a 3 x 10 minute interval session, and you do 310,298,288 watts for the three intervals, your session average is 299 watts. Below we have included an example from an athlete. Plotting your data in such a way will ensure that you are progressing. It will also warn your when recovery is insufficient. When you have not recovered sufficiently, you power would drop. This can be rectified very easily through including more rest.
Figure 2: A diagram showing session analysis of all 4 minute (typically 6 x 4 minute intervals with 2.5 minutes rest) and 2 minute intervals (8 x 2 minute intervals with 90 second rest) that a certain athlete has performed. These sessions are analysed to ensure that the session average (shown on the figure with a short horizontal line) is improved from session to session.
For this reason, we as coaches like sticking to a standardised training sessions which we often like repeating so that we can compare apples to apples.
Will a power meter help me when racing?
When we talk about racing with a power meter, we instantly have the picture of Chris Froome staring at his stem in our minds. Yes, we may be able to pace ourselves during a MTB race with a power meter, but we still have to ride over the obstacles the course presents. Therefore it becomes more complex. Due to the terrain, MTB power data becomes extremely stochastic (highly variable) in nature. Because of this, the metric “normalised power” is often used to quantify the physiological stress over a certain period. By definition, a maximal 1 hour effort should yield a normalised power equivalent to your functional threshold power (see the text box explaining these terms). Your intensity, as can be shown by your intensity factor (again, see text box), may therefore be a good metric to use to ensure that you are not pushing too hard at the start of a MTB marathon race. To avoid blowing up I normally warm mountain bikers taking part in long marathon races to ensure that their IF is never >0.9 during the first hour. Using that as a gauge and warning for pushing too hard will see you finish hard and avoid the dreaded bonk.