Power and Running?

January 31, 2021

Power and Running?

Over the past 12 months, we have seen a new piece of technology grow in popularity in Running - the power meter.

A lot of Cyclists and Triathletes understand the concept of power as a training metric and use a cycle power meter to gauge effort. It means they can race at the optimal level of exertion and avoid fading in the later stages.

So, why exactly should you use a power meter? To measure apples and apples, not apples and oranges…

When using pace or heart rate as your metric for race or training effort you are not comparing like for like on mile or km splits. Obviously, when running uphill vs downhill your pace should be adjusted to maintain a consistent effort throughout. HR has other issues - lag (it doesn't normally Increase until after the effort has started) and can be raised due to caffeine intake, higher cortisol or adrenaline and it even drifts over time on longer runs. So if you want to put in a consistent effort on a run, be it a race or training session then power is your number to watch.

What is Power?

Power is a measured in Watts (joules per second) so it's a rate of energy burn or more technically the rate of energy transfer and in this case, the conversion from potential (mostly glucose) energy to kinetic (movement) energy.

The basic physics are -
Force = Mass x Acceleration
Power = Force x Velocity

A power meter typically measures acceleration and velocity using 3D micro accelerometers, similar to the ones found in your smartphone or sports watch. You calibrate a device with Mass by inputting your height and weight, then through some high powered processing ability, some very clever maths and complex algorithms, it punches out a real-time power number using the formula above.

How to race with Power?

Once you have used a power meter for a number of max exertions over a set distance (say 5k) you will know what your critical power is for that time duration, for example, 320 Watts. This is the maximum effort you can endure over that distance for your current Mass and level of fitness. You can then estimate with a high degree of accuracy what your critical power is for other distances like 10k or Marathon.

Now you will know the effort level you need to target on race day and you should be aiming to run the whole distance as close to your critical power (for that duration) as possible.

Setting off at the critical power pace will probably feel steady-fast the flats, slower than you expected on the uphills and faster than expected on the way down (that's my experience anyway). By using Power you'll be maintaining a consistent effort level and will likely avoid the dreaded oxygen debt zone. That means a strong and surging finish and a positive end to the race assuming nothing else goes wrong :)

Hopefully some insights there for those of you who were already intrigued by the new technology. Otherwise sorry for taking up your Strava feed this Saturday.

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