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Making Sense of Your Powermeter Data – Golden Cheetah

Home » The Training Hours » Making Sense of Your Powermeter Data – Golden Cheetah

In my previous post, I explained how the body responds to different type of exercise (physiological/training) stress. Improvement is based on that response.

You need to be able to evaluate and quantify the stress you put your body through day after day as you train ie “How fit do I get after 1h riding at Z2 or Z3, 5x5min at Z5 etc.” You need to make sense of the mountains of data your powermeter records. First you need a software like Golden Cheetah (or WKO+ or Cycleops Power Agent). Second, there are a couple of terms that need explaining.

The Termninology Made Easy

How Hard for How long = Training Stress

This is the basic principle when it comes to analyzing the training stress you put your body through. How long as you probably guessed is easy to figure out.

How hard?

What is considered hard? In simple terms your human engine redline (or Functional Threshold Power – FTP) is the hardest you can sustain for 1 hour. Therefore for any given length of time, anything below that is less than 100% anything above is more than 100% effort.

When you go for a 1 hour ride, your bike computer records average power let’s say 200W. You have an FTP of 250W so by initial glance that 1 hour ride was certainly not too hard.

Although, the ride could have gone in a couple of ways.

  1. You rode nice and steady at 200W all the time (on a trainer or a flat road with no wind)
  2. You rode the first 30min leisurely at 150w and you decided to pick up the pace in the second 30min and rode 250W.
  3. In a criterium you were constantly slowing down and accelerating out of corners so your power looks something like 30s at 75W average and 30s at 325W for a full hour.

In all three cases your hour average is 200W. HOWEVER…

  1. You worked at about 80% of your max
  2. In that second 30min you worked quite hard (at your FTP)
  3. You went above your FTP quite often, really pushing it.

So how can you quantify how hard you worked in those three situations?

xPower (Normalized Power)

Power analysis software like Golden Cheetah (or WKO+) uses a term called xPower (Normalized Power). It is a mathematical formula that samples the data differently so it gives a better overview of the how hard you work during your training.

So if we go back to your 3 different 1 hour rides your xPower looks something like this

  1. 200W
  2. 225W
  3. 260W

Therefore xPower is the first metric when it comes to understanding how to analyze your power meter data. It is the better overview of “How hard?”

Relative Intensity

This is how your xPower relates to your FTP. When NP = FTP intensity is 1.

So…

How Hard x How Long = ????

So now that you understand the “How hard?” and “How long?” parts, we need a metric to put them together.

Golden Cheetah uses a metric called Bikescore to estimate your training stress based on your xPower. The higher the number the harder you worked that day. Therefore instead of tracking how many kilometers or how many hours you did in a a week, you can use Bikescore.

Improving Over Time

As you train you accumulate training stress (Bikescore), therefore you should be supercompensating in response and getting fitter. There is a formula that Golden Cheetah uses to estimate that supercompensation.

It boils down to two terms: Short Term Stress (STS) and Long Term Stress (LTS).

  • Short term stress (Fatigue): this represents your training stress averaged in the last 7 days.
  • Long Term Stress (Fitness): This is the training stress over 6 weeks (42 days). When you first  start training it is 0.

When you subtract STS from LTS you get Stress Balance (SB) or also known as Freshness.

Negative stress balance means that you are not fresh, however, to improve, your STS must be higher than LTS

Positive balance, means you are fresh.

In general fit and fresh is where you want to be at races.

It is a balance between Fatigue, Fitness and Freshness.

After some time you end up with a graph like this one. I will cover Golden Cheetah in detail in my next post.

STS (Pink), LTS (Blue), SB (Yellow), Bikescore (Purple bars)

A very popular and probably the first software to “put all that together” was WKO+. Although it uses different terms, the principle and the numbers behind it are very similar so for your convenience I am including a glossary of the terms WKO+ uses and their corresponding therms in Golden Cheetah.

WKO+ and Golden Cheetah glossary

Acute Training Load (ATL) = Short Term Stress (STS)

Chronic Training Load (CTL) = Long Term Stress (LTS)

Normalized Power (NP) = xPower

Stay tuned for my next post on Training With a Powermeter where I will cover knowing your way around Golden Cheetah.

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