Journey2Ultra Running Coach Journey2Ultra

How do I know if I’m improving as a runner, measuring performance.

As your running training progresses a genuine question to ask is, "Am I improving as a runner and is my training working?"

Whilst we can point to the obvious progressions in terms of more volume (distance), and increased intensity (faster intervals), what if there is a metric that not only shows progression, but it can also be used to individualise all your training sessions, plans and provide an excellent insight into race performance.  Tracking performance is not just for the elites of the sport.

Enter Critical Power or Speed (CP or CS).  What is CP/CS, how do we measure CP/CS and then how do we use it to individualise your training and apply to racing?  We look at these questions in the context of an athlete I am coaching for a marathon in several months’ time.  Whilst there is a fair bit of science behind the principles, it is very easy to use effectively.  It should be noted that CP/CS is just as relevant for all running levels, events and training, including trail and ultras!

What is CP/CS?

The Norwegians are currently having a lot of success on the track and in triathlons, there’s focus on their training and specifically “Double Threshold Sessions.”  Whilst these require lactate meters to accurately measure blood lactate to determine lactate threshold.  A more important threshold and more practical, I would argue for most of us runners, is CP/CS.  In a simplistic term, CP/CS is the dividing line at which you can run for a long time (think those easy long runs) or exercise harder and you must stop much sooner (hill sprints).

Running under CP/CS your blood lactate is stable, above CP/CS your physiology becomes unstable, till you can no longer keep going.  Think how you feel at the end of a tough interval or speed session!  Going above CP/CS will mean you will eventually fatigue and is accurate enough that we can calculate the point of fatigue to within seconds.

How do we measure CP/CS?

To measure your CP/CS is simple and no need for expensive lactate meters!  All you need is to do a couple of runs (running as hard as you can) and record the info.  A short test of three minutes and a longer run of 10 to 12 minutes.  Both tests can be completed on the same day with a good rest between the two runs of 20 to 30 minutes.  If you have a running power meter like a Stryd, you record the average power of the separate runs to calculate CP.  If you don’t have a Stryd, you just need the distance covered for the separate runs to calculate CS.  Below is an example of three live tests conducted several months apart.  With the data punched in to calculate, in this case CP.  I won't cover here the specifics of the calculation and happy to go into in more detail if you reach out.

The positives of doing this kind of test, is its functionality, you’re out there running just like in a race!  The data below shows test completed in January, April, and June, with CP increasing from 313W to 352W.

Critical Power Calculations

How do we use CP/CS to individualise your training?

Now we have your CP, we can individualise your training to your physiology and each of your different training sessions and the specific physiological adaptation we are looking for.  The table below shows the zones as percentages and calculated as a power target.  If you don’t have a power meter, you can use pace zones as effectively (CS has a slightly different calc going from CS in metres per second, to a min/km pace).

For example, for this runner’s easy sessions, we would not want them to run over 299W.

Running Zone Calculations from Critical Power

The improvement and applying to a race.

Through individualised training and regular CP testing we can see in the case of this marathon runner their CP increasing from 313W in January to 352 in June.  Putting this in simple terms, they are now running faster and longer!!

This athlete has completed two half-marathons in prep for their full marathon in September.  The first of these was run in May, and we used the following targets to pace the race:

  • Upper – 320W time of 1h39m

  • Goal – 316W time of 1h40m

  • Lower – 310W time of 1h42m

For this race the runner completed in 1h42m, whilst at the lower end, still a great result and deliberately run a bit more conservatively.  Fast forward to July and another half marathon:

  • Upper – 345 time of 1h31m

  • Goal – 337W time of 1h34m

This time the runner completed in a time of 1h32m (342W avg.), knocking a whopping 10mins of the time in May and placing in the top ten!  All achieved through the hard work of the runner and individualised training and pacing for racing.

Whilst there is a fair bit of science behind this, as a coach that’s where I come in, and keep it simple for you.  All you have to do is run!  Reach out if you are interested in learning and applying these principles to your training.


Skiba, P. F. (2004). Scientific Training for Endurance Athletes. (K. E. Beebe, Ed.)