Nick de Meyer TBCUK Master Coach
This is a question I have been asked many times as a coach I hope this posting helps to simplify what it is and how it relates to other, better known measures, like heart rate.
Let’s backtrack a bit and answer the question: What is power? Power is an excellent method of measuring exercise effort or intensity and has become the most important measure with professional cyclists in particular. It is favoured by the pros because it is seen as a more accurate measure of performance. It is normally measured in Watts and, like heart rate, can be used in percentages of its maximum output to define training zones. Power measurement is immediate and doesn’t have the delays associated with heart rate. No sooner you push harder on the pedals it registers wattage, where as heart rate does not respond instantly to effort, it usually is delayed for 15 to 20 seconds.
To measure power you need to fit a power meter to your bike, there are now a number of these devices around and are becoming much more accessible. In the next few years you will see almost every road bike fitted with a power meter as the technology is refined. (You heard it here folks!)
In essence, Critical Power (CP) is a method to measure your power output. It’s basically the highest average power you can hold for a particular period of time. Just like training at different heart rate levels can improve your overall fitness; training at different CP levels will do the same. Dr Andy Coggan the brains behind the methodology developed CP zones from 1 minute to 360 minutes (seen in blue on the attached table). As you adapt and get stronger and fitter from following your training programme, these numbers will improve, relative to the goal of your training plan, and dependent on which phase of training you are in.
CP 60 and Lactate Threshold
This is the wattage number that triathletes find most useful. Most of us involved in competitive Triathlon or Cycling will have heard about Lactate Threshold (LT), no doubt we will have all felt it on a tough ride. This is the point when we are riding when there is a rapid rise in the blood lactate level. It’s when the body's rate of lactate production exceeds the rate of lactate clearance. This causes that burning feeling in the muscles and can cause a slowing of our pace. This level of intensity can be maintained in a typical standard distance triathlon race or 25 mile cycling time trial and in some cases a bit longer. For this reason, and the fact that it is very sensitive to training status, LT is a very valuable piece of information for planning training intensities and race pacing strategies. This Lactate threshold level represents critical power for 60 minutes or Functional Threshold Power as it sometimes known. All our training zones are then based on % of this number.
How can I use this?
To establish your baseline “Functional Threshold Power” (FTP) you need a power meter or turbo with wattage. Warm up well and then start a 10 mile or 30 minute time trial. Hit your lap button after 10 mins and record your highest average wattage. Then subtract 5% from that total. The reason that we are subtracting 5% of the watts from your 20 minute test is that FTP is defined as the highest average wattage or power that you can maintain for 60 minutes. Most athletes have a hard time focusing for 60 minutes on a maximal effort and those that can, learn very quickly that a 60 minutes time trial is not that much fun! Testing at 20 minutes is more realistic in terms of getting athletes to do more regular and higher quality tests. Use it every 4 weeks or so to chart your improvements. Use the % in red seen in chart below to calculate your training zones as a % of your FTP:
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