Power is Knowledge
A power meter doesn’t care about hills, wind or temperature. It simply measures the actual power you are producing, and this data combined with information about your heart rate indicates the body’s response to the workload. This amounts to a powerful training and race-pacing tool.
Key advantages of knowing your exact power output:
- Setting and sticking to a predetermined target power can ensure you do not overdo things at the start of an effort or fade towards the end, when it really counts.
- Workouts can be downloaded, analysed and compared long after they have been completed.
- Fitness changes can be tracked and exact improvements measured. This combined with the TSS (Training Stress Score; discussed below) can allow the athlete to plot performance changes clearly.
- Through constant evaluation, riders can determine and modify their training zones and his capabilities, thereby raising the performance bar continuously.
Training Stress Score (TSS )
The Training Stress Score is a benchmarking tool that allocates effort points to workouts, based on an analysis of the power/work data recorded by the power meter. A simple calculation can help to track current fitness levels and help the athlete to plan how many points need to be scored by different types of workouts, or over a complete programme, in order to reach a specific goal or peak for a particular event.
The TSS calculation can be defined as:
TSS = (sec x NP x IF)/(FTP x 3600) x 100 where
- sec is the duration of the workout in seconds
- NP is Normalised Power (a statistically modified average power figure)
- IF – Intensity Factor (a percentage of your FTP – how intense the effort was)
- FTP is Functional Threshold Power (your best average power for a one-hour race or test)
- and 3600 is the number of seconds in an hour.
TSS is relative to your own capability and power to weight ratio. So one hour at FTP would cost you and Chris Froome the same (100 points). But because he has a higher power to weight ratio he will have to
work at a higher average speed. A day at the Absa Cape Epic would typically produce about 350 TSS points at an IF of about 0,7, i.e. a TSS of 50/hour. The Discovery 947 Ride Joburg would have a TSS
of about 200–260 depending on pace. Here TSS per hour would be higher because of the shorter duration, maybe 85–90 at race pace. The bike leg of an Ironman triathlon would generally be ridden at an IF of
about 0,75 for a TSS of 280 in order to leave enough reserves for the run.
Here we can see a graph of a typical six-hour endurance ride. Power is shown in yellow, heart rate in red and cadence in green. The first three hours were done at a 198-watt average with a 124 beats per minute average heart rate. The last three hours were done at an average of 199 watts with a 134 beats per minute average heart rate. The variance in heart rate is eight per cent. Without the use of a power meter, the cyclist might think he is no longer training in the correct heart rate zone and back off, thereby not achieving the desired training effect.