Home Cycling Tips 8: What is a power meter and what it is for?

A power meter on a bicycle is a device that measures the power delivered by the cyclist. Most bicycle power meters use strain gauges to measure applied torque and, when combined with angular speed, calculate power.

Power meters generally transmit wireless data and can be paired with standard bicycle computers. They provide instant feedback to the athlete and allow for a more accurate race analysis. For some years now,  the use of a pedalling power meter has been used in professional cycling both in training and in managing the rhythm of the race. Even in the amateur world, albeit more slowly, we are going towards this direction, although the price of this instrument is still high.

Today, It is rare to find a professional cyclist or triathlete that does not use a power meter for training and competition. Reading the data expressed by these instruments allows the cyclist to measure the power he imprints on the pedals accurately, taking into consideration all external conditions: wind resistance, slope and smoothness of the road.

With this data, you know precisely and objectively how much you are pushing on the pedals to make the bike move.

In order to obtain similar data, speedometers and heart rate monitors have been used since the 1980s. However, these instruments only provide indirect data on the physiological response to exertion. Furthermore, the latter still remains a rather imprecise instrument.

In fact, heart rate monitors, although directly related to the level of physical effort, are also influenced by factors such as performance anxiety, use of exciting substances or daily changes in hormonal rhythms. Think of the athlete who trains alone for 50′ in anaerobic threshold at 160 bpm with good fatigue; the day of the race, after two coffees and feeling the excitement of the group proceeding, the same athlete can easily reach 170 bpm over the same period of time.

According to sport-gadgets.net, power meters can be divided into four main types:

• by crankset
• pedal
• cleat, hub, crank
• dumbbellIn a power meter, the most important requirement to evaluate is the accuracy of the data, as a difference of a few watts can be very significant in performance evaluation (in most cases the accuracy decreases as you move away from the cranks). The data collected by these instruments include peak, instant, average and interval power. In addition, in some models of power meters, you can detect the difference in thrust between the two legs (also called balance).The idea of instantaneously measuring the watts delivered by the athlete stems from the need to quantify more objectively the effort required by competitions and training. With the possibility to store the collected data, through dedicated software, it is possible to study them afterwards, thus elaborating workout programmes and schedules.

From frequency to threshold power with the power meter

The opportunity to know the power expressed has led sports coaches and doctors to draw up training programs based not on heart rate percentages but on those of power.

We have therefore moved from percentages based on threshold frequency to those based on threshold power. The result? Easier to follow training loads and better control of performance and improvements.

How is power measured?

The power, or energy produced in a given fraction of time, is expressed by a measure of intensity known as watts. One watt equals 1 joule per second, and one joule equals the energy required to move a mass of 1 Newton (more or less 100 g.) per meter.

When you look at the display of the instrument on the bicycle then you read a value corresponding to the total energy needed to move your body mass against a certain resistance, in the bike determined essentially by:

• body weight,
• rolling friction,
• air resistance.

The power, instant by instant

A power meter then provides proven data measured in real time: It is the power with which you push on the pedals, and the watts are always the same. Today's 100 watts are tomorrow's 100 watts, a unique and objective value. In addition, they are provided by an instant and direct reading of the effort, even if it lasts a few seconds.

Always knowing the power that is being delivered is essential for the planned training on the watts, especially when the intervals become thinner and it is necessary, and even more difficult, to carry them all out at the right intensity. If you have for example to start with 350 watts at the first repetition, you have to get to the last one with a very similar load.

If you don't have the power indication, you generally start stronger and stronger, for example with 500 watts, and consequently you will have to go down in intensity towards the last repetitions, arriving, for example, to push only 250 watts. The exercise is no longer as prescribed and the result is not as expected.

The power meter must be accurate

The power measurement must be precise and repeatable. A 3-5 watt error is not significant, but if a system is not reliable there may be deviations of many tens of watts, i.e. equal to or greater than the amount of power that is gained from one year's training.

It is good to be aware that in order to make assessments of your ability to express power you need to use the same test protocol and the same equipment.

There are a number of power meters, each with a number of features and price differences. Remember that a power meter is never better or worse, but rather it is about finding the one that fits your budget, is compatible with your bike and offers the features and functionality you want.