Whether you have a power meter on your road bike or you use a smart turbo trainer with a power meter built-in, power meters are a useful tool for measuring your efforts and tracking your fitness progress.
Power meters are certainly getting more affordable, but knowing what to do with one to get the most out of your training is a different matter.
Jon Sharples of Train Sharp Cycle Coaching explains: “The main benefit is to give you real time information so that you can gauge your effort.”
It’s not just about looking at your numbers after a ride, though: “Simply looking at the data afterwards will not let you make the most of your training ride or pace your race effectively,” says Sharples.
What’s the benefit of using power over heart rate?
“Factors such as hydration, energy levels, overall muscle fatigue and temperature can have a huge impact on heart rate, so you can never really be sure if there is more to give or if you should back off to conserve your energy,” explains Sharples.
Unlike a heart-rate monitor, a power meter shows the work you’re doing right now: “This gives riders huge pacing benefits as they will know the numbers they can ride at for a set distance and stick to them. This is without doubt the most efficient way to tackle long distances.”
What is a power meter actually showing, though? “A power meter is your on-board energy display [using watts to measure work] so the biggest advantage is that it allows you to train in the correct energy zone for your desired event(s),” explains Sharples. “If you are concentrating on 25-mile time trials then the only energy system that you want to build is the one that enables you to ride as hard as you can for one hour.”
Essentially, the benefits are...
- Pace with perfection
- No drift, as with heart rate
- Train accurately
- Track your fitness
- Know when to rest
How to get started with a power meter
First off, you're going to need a power meter. There's pedal-based, bottom bracket-based, chainring-based and crank-arm based systems, some that measure from only one side and others that are double sided. Which one is best to go for all depends on how you intend to use it, your bike, your budget and if you want to use the power meter on more than one bike - our guide on the best power meters is a really great place for finding a power meter that will suit your needs.
But a power meter is no more than an expensive number-generating machine unless you know what you are doing with the data and apply it to your training.
The very first thing you need to do when you get a power meter is to perform a fitness test to establish your training zones.
The gold standard test for power training is the 20-minute FTP (Functional Threshold Power) test. Functional Threshold Power represents your sustainable continuous power output for 60 minutes. Regular FTP testing can show if your fitness is improving and ensures that you are working in the correct training zones.
Sixty minutes of effort is physically and psychologically taxing, so to allow for more frequent testing your FTP is calculated from the highest power you can sustain for 20 minutes, multiplied by 0.95. An FTP test requires an extensive warm-up followed by a recorded 20-minute effort. It is not easy to do and requires some pacing to ensure that you finish spent but are still able to complete the test.
Once you know your FTP you can calculate your training zones as follows:
How to use power data to set a training plan
To improve your fitness, your body needs the right mix of hard training and effective recovery. However, without a power meter giving clear, accurate data it is very easy to train either too hard, or too easy, to get your desired results.
Power meters are especially useful for performing intervals, particularly short ones. Unlike heart rate there is no lag in the feedback so your training effort is precisely the right intensity for the full duration of the interval. “Very short, intensive intervals are not possible to judge using heart rate,” says Sharples. “By the time the heart speeds up to keep up with the muscles, the effort is often over.”
Getting to know your power output compared to heart rate is also a useful way to determine whether your training is working, Sharples explains, “Riding with power and heart rate allows you to track aerobic conditioning. If your heart rate starts to drop for the same power you are becoming more efficient [fitter].”
It can also pre-warn you of illness or overtraining when used in conjunction with a heart-rate monitor: “If your heart rate reads much higher or lower than normal for the same wattage that’s a good indication something’s not right.”
How else can you get the most out of a power meter?
Pacing gives you the edge over your competitors
If you know your threshold, you know what you’re capable of over a given amount of time, meaning you know you rode the fastest time possible in your TT or sportive.
Find out whether you’re getting the most out of yourself in races
Tracking power allows you to compare training with racing so you can see if your pre-race taper is actually working, or whether a different strategy is needed.
Compare yourself to previous years with accuracy
Your time in an event can change according to things like the road surface and weather conditions, and heart rate is affected by multiple factors. Power isn’t changed by outside variables so you know if you’re improving or not.
Learn how to pace effectively
Set off at a power in your endurance zone — it will feel easy to begin with. Four hours in it will be hard to maintain but you’ll have done the most work.
Your device’s instruction manual will tell you how to do this. It ensures you’re not riding with numbers higher, or lower, than reality and are training at the right level.
Say goodbye to ‘junk miles’ — the training that makes you tired but not fitter
If you ride with power there’s no denying when the numbers are down and it would have been better to have a day off.
Power meter data mistakes to avoid
– Failing to bear in mind whether average power includes freewheeling time, which dramatically affects the number.
– Confusing simple average power with normalised power. Normalised power accounts for intervals and efforts that have occurred over the entirety of the ride. Average power will simply average out the training session as a whole, which can lead to misinterpretation of more intense sessions that may have been more fatiguing.
– Forgetting to ‘zero offset’ a power meter before riding and then relying on inaccurate data. Think of zero offsetting a power meter as the same process as resetting a set of measuring scales. Air pressure, ambient temperatures and other things can alter power meter readings in between rides. Therefore ‘zeroing’ your power meter before each ride clears the residual torque and sets an accurate baseline to work from.
– Failing to acknowledge the differences between indoor and outdoor riding: the former involves zero coasting and no air resistance, whereas outdoors there are many variables such as wind and drafting gains.
Training data glossary
Many power meters and training plans convert training effort into stress, load and fatigue scores. If your power meter is outputting additional figures, here's how to understand them…
Training Stress Score (TSS): The number that relates to the intensity of a single training session. The higher the number the more strenuous it has been.
Acute Training Load (ATL): The short-term fatigue number that is accumulated, estimated over a seven-day period.
Chronic Training Load (CTL): The longer-term fitness accumulation rating based over a 42-day period of time. Rides that are completed more recently will be more weighted towards this number.
Training Stress Balance (TSB): This number is the difference between CTL and ATL and addresses whether a rider may be approaching top form. When this number is positive it indicates a good performance is approaching following a decent block of training combined with a low recent value of fatigue. This is where the tapering effect comes to fruition.
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