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Power analysis of a circuit race with TrainingPeaks

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Knowledge level: Intermediate

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Article posted: 09/07/2014

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The world’s best cyclists prove that training smart is the key to world class results. But you don't have to be on the GB Cycling Team or an elite coach to use the exact same software for planning and analysing training, nutrition and daily metrics.

British Cycling has teamed up with TrainingPeaks, our Official Training Software Supplier, to provide discounts to both cyclists and coaches that are members of British Cycling

TrainingPeaks are also producing exclusive content to help you optimise your training and make the most of the packages they offer. In this article James Spragg of Dig Deep Coaching analyses a real ride file of one of his coaching clients. If you need to remind yourself of the key metrics used by TrainingPeaks, look at their Getting Started on TrainingPeaks article.

Criterium racing is a very specialist discipline within cycling. Racing around a small circuit lap after lap for between 40 minutes to 1 hour presents a unique physiological challenge. Let’s look in detail at a power file from a criterium and see just what physiological characteristics are needed to perform well.

The file below is taken from a Matrix Fitness Grand prix series - the premium criterium series for women in the UK.

As can be seen from the file the course involved 18 laps of a 1.46km circuit. The graph below shows the profile for one lap of the course. The course has 4 corners and includes a 500m drag at 3.8% grade.

Now we have an idea of what the course looks like we can have a look at the physiological demands of the event.

Normalized vs. Average Power

The first thing to note is the average power for the 45 minutes, here the athlete averages 218W. What is more interesting however is the Normalized Power® (NP®) of 253W. Normalized power is a much better reflection of the physiological demands of a criterium. Due to the amount of time spent not pedalling in the corners or ‘soft pedalling’ into a corner the average power for the effort is low. Normalized Power however takes into account the physiological effort of sprinting (or ‘kicking out of’ as it is often referred to) after each corner. This is illustrated in following charts.

The dotted line above represents where the athlete’s Functional Threshold Power (FTP, or what a rider can hold for a 1 hour all out effort) power would fall on the graph along with where their power zones boundaries would fall. As the pink line shows, the athlete was almost exclusively in either zone 6 or in zone 1. The zone 6 sections represent the effort kicking out of a corner and the zone 1 or 0 power sections represent the ‘soft pedalling’ or no pedalling in the corners. The chart here illustrates this perfectly.

During the criterium the athlete actually spent more time in zone 1 than any other zone, the next most frequent zone was zone 6. This all or nothing power distribution is where the discrepancy is created between the Average Power and Normalized Power.

Intensity Factor

The rider’s Intensity Factor® (IF®) was also very high for the effort 1.044. This means that the athlete’s NP was actually 4% higher than their FTP. Average power however was below FTP at 218W. The difference between AP and NP gives rise to a very high VI for a criterium. In this case the VI was 1.16.

Heart Rate

Although this article is mainly looking at the power production during a criterium it is also interesting to compare the athlete’s heart rate trace to their power output. The chart below shows the heart rate distribution during the effort.

    

Heart Rate and Power

These two charts show something very interesting. They show that during the criterium the athlete’s heart rate was consistently in zone 4. Even during the periods where the athlete was riding in zone 1 their heart rate wasn’t falling. The reason for this is that the periods in zone 1, despite totalling where the athlete spent most of their time, were all very short. These periods were insufficient to allow the heart rate of the athlete to drop. What is actually happening in these periods is that the athlete is recovering from the zone 6 effort they have just made. The graph below illustrates this.

The red arrows represent where the athlete was making an effort, the black arrows represent where the athlete was recovering. Heart rate however remained fairly constant through the effort with only a difference of 7 bpm between the maximum and minimum heart rates during this lap.

What can be seen is that a criterium is actually a series of sprints out of corners followed by periods of recovery. It is no coincidence that the graph above shows 4 periods where the athlete was making a zone 6 effort and there are 4 corners per lap in the criterium. If we then consider that this race consisted of 18 laps that is a total of 72 sprint efforts in 45 minutes.

What does it take to be a good criterium rider?

Firstly a high FTP, with Average Power being low for a criterium this may seem odd on first inspection, however if we look at FTP as being the maximum average wattage that can be sustained for 1 hour then it follows that the all efforts within a criterium can only add up to FTP power.

What is also important to note is that the effort after each corner is not a 100% max effort sprint. It is instead a zone 6 acceleration, this needs to be completed after each corner. Therefore during each of these accelerations a rider with a high FTP will be working at a lower percentage of their ftp for the same acceleration.

To illustrate this we can compare 2 riders. Rider A is 75kg and has an FTP of 350W, rider B is also 75kg but has an FTP of 300W, for this example a 5s 700W effort is required to get back up to speed after a corner.

During this effort, Rider A with an FTP of 350W is working at 200% of FTP whereas rider B with an FTP of 300W is working at 233% of FTP power. Because this effort needs to be reproduced up to 80 or 90 times a race rider B has to work 33% harder for almost half the race. This will leave rider B with less in the tank towards the end of the race.

In addition an athlete will not start to recover from an effort until their power output falls below FTP power. Therefore if 325W is required to stay with the bunch after the initial acceleration after a corner then Rider A will be recovering whilst Rider B will be in the red.  This will mean that rider A is ready to make another acceleration following the next corner whilst rider B won’t be.

The next characteristic needed is the ability to complete repeated zone 6 efforts. The ability to do this without fatigue setting in will allow a rider to stay with the bunch or attack later in the race. A rider with a high max power output will be working at a lower percentage of their neuromuscular and anaerobic capacity out of each corner. We can look again at riders A and B to illustrate this. Rider A has a 5s peak power of 1200W whereas rider B has a 5s peak power wattage of 1000W. For Rider A the 5s 700W effort out of each corner represents only 58.3% of their peak 5s power whereas the same effort represents 70% of peak 5s power for rider B. Therefore the effort is easier to repeat 80 or 90 times for rider A than rider B 

In conclusion both a high FTP and the ability to produce high short term power make for a perfect criterium rider.

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