So what is a power meter? Quite simply, it is a tool which can measure the amount of force (watts) the rider is exerting to move the bike forward. Some meters measure this in cranks, others the pedals, bottom bracket, or hub. It doesn’t matter where this force is measured, the key thing with a power meter is that the measurement of this force is objective and a constant. A watt is a watt. Here lies the benefit of training with a power meter; it allows the rider to get an quantitative measurement of their ride regardless of external factors which affect a rider. This is important, because ultimately cycling performance is based on a power to weight ratio and of course their endurance. If you train by heart rate alone, it is very hard to get objective data. A rider’s heart rate could be affected by many external factor such as time of day, caffeine intake, sleep quality, stress levels, weather, fatigue level etc.
Planning to ride at a certain BPM range or evaluating your ride based on average and peak BPM’s can be quite misleading because of these factors. If you train by speed/distance it is also difficult to get truly comparable data. For example, “I did a personal best on my favourite hill climb”, however factors such as weather, bike setup, time of day, clothing – even tyre pressure will all be a factor. It’s very hard to get all the variables the same each time you want to test yourself. This is where a power meter becomes invaluable. It takes all these external factors from the equation. You complete your ride or test and look at the wattage output. It does not matter if you were riding into a head wind, with knobby tires and wired on caffeine. You can compare your wattage output to other rides in different setups and even across different bikes. You might be slower up your favourite hill due to external factors, but you might actually be putting out more watts and be a stronger rider then you were before.
Because a power meter enables these objective comparisons, it is possible to “score” the intensity of every ride you do. This score is relative to your threshold power. To put this another way, before starting to train by power you first need to baseline your power output. This is called a threshold test and usually involves an all out 20 or 60 minute effort.
From the data obtained in the threshold test, every ride you then plan or do is relative to this threshold. Whether it be a recovery, endurance, tempo, SST, or VO2 session, all the wattage targets are relative to your threshold test. So you can accurately plan to ride in certain power zones to work on a specific aerobic, anaerobic or muscular system.
Similarly, post ride you can calculate the overall impact of this ride on your body. By tracking this we can accurately measure the physiological load on your body over time and so can plan the phases of training and physiological adaptation without overtraining the rider and causing regression.
Finally, the next time you do a threshold test it’s easy to objectively gauge your improvement. Simply compare your power to weight ratio from each test and it’s easy to see an improvement or decline.