Thursday 27 November 2014

Power Zones - % FTP or Peak Power?

Looking at this screenshot from Golden Cheetah got me thinking about power zones. It's in French, but it demonstrates the point better than the English screenshots I could find:

Golden Cheetah, like just about everything/one else, seems to take FTP and assign a % range for each of the zones. I noticed though, that the zones were quite closely aligned to key points in the Peak Power Curve: z3 between 1 and 2 hour peak power, z6 between 1 and 3 minutes.
Since riders are all different, it seems inaccurate to assign their training zones to standard % ranges, rather than to customise them to their specific abilities using the data available.
For example my own, not very wonderful, power curve looks like this:



Adopting peak power based, rather than % of FTP based zones would result in some differences:
Since my target race distance is 180 km, it is not surprising that zones 1 and 2 finish higher than a typical profile. It is perhaps surprising that zone 3 finishes lower. That is probably a personal weakness where I need to devote some time. Zones 4-7 are a bit higher than typical. Arguably, today I am pushing too hard when I'm aiming for z3, but not hard enough in all the other zones.

Another approach would be to assign different % ranges depending on generic rider types. Dr Coggan proposed several generic rider types here:
home.trainingpeaks.com/blog/article/power-profiling
He compares actual power outputs/kg to a standards table and looks at the resulting profile shape, categorising riders as:
  • All Rounder
  • Sprinter
  • Time Triallist/Endurance
  • Pursuiter

Perhaps the % ranges should be adjusted for each rider type? Endurance riders might see zone 6 starting a little lower - 110% for example. Zone 7 would similarly be lower. Sprinters might see Zone 3 start a little lower 75 or 80% perhaps.

Friday 21 November 2014

The Effects of Age on Functional Threshold Power

Dr Coggan wrote a very good piece on how Functional Threshold Power declines with age here:
Successful Aging and Functional Threshold Power
The conclusion being that FTP w/kg declines on average at 0.04 w/kg/yr after 40 years old. After the FTP test at our club this week (see previous post) we were discussing how to compare the results of the younger guys with us old war horses.

It seemed to me that I might answer the question from another direction using the Veteran Time Trial Association Standards Tables and the well known equation for power (Martin et al 1998):
(g is Earth's gravity, m mass of rider+bike, Vg speed over ground, K1 is a constant representing rolling resistance, s slope, K2 a constant representing drag, Va is speed through the air)
I made some reasonable assumptions - flat course, still conditions, rider of 75kg and 8 kg bike, etc. and arrived back at exactly the same result for both men and women! I varied the rider and bike mass and the results did not vary to a significant degree. Whilst my results validated the average reduction per year, it was not linear. Up to age 65 average reduction per year was less than 0.04. After 65 it increased quite rapidly as shown in the graph below:

So at age 55, my FTP/kg of 2.85 is comparable to 3.45w/kg for a <40 year old. To arrive at your own age adjusted w/kg subtract 40 from your age and multiply by 0.04 then add to your FTP/kg. If you want to know how you compare to others you can then look yourself up in the table prepared again by Dr Coggan:

Maximal power output (in W/kg)
MenWomen
5 s1 min5 minFT5 s1 min5 minFT

24.0411.507.606.4019.429.296.615.69
23.7711.397.506.3119.209.206.525.61
23.5011.277.396.2218.999.116.425.53
23.2211.167.296.1318.779.026.335.44
World class22.9511.047.196.0418.568.936.245.36
 (e.g., international pro)22.6810.937.085.9618.348.846.155.28
22.4110.816.985.8718.138.756.055.20
22.1410.706.885.7817.918.665.965.12
21.8610.586.775.6917.708.565.875.03
21.5910.476.675.6017.488.475.784.95
Exceptional21.3210.356.575.5117.268.385.684.87
 (e.g., domestic pro)21.0510.246.465.4217.058.295.594.79
20.7810.126.365.3316.838.205.504.70
20.5110.016.265.2416.628.115.414.62
20.239.896.155.1516.408.025.314.54
19.969.786.055.0716.197.935.224.46
Excellent19.699.665.954.9815.977.845.134.38
 (e.g., cat. 1)19.429.555.844.8915.767.755.044.29
19.159.435.744.8015.547.664.944.21
18.879.325.644.7115.327.574.854.13
18.609.205.534.6215.117.484.764.05
18.339.095.434.5314.897.394.673.97
Very good18.068.975.334.4414.687.304.573.88
 (e.g., cat. 2)17.798.865.224.3514.467.214.483.80
17.518.745.124.2714.257.114.393.72
17.248.635.014.1814.037.024.303.64
16.978.514.914.0913.826.934.203.55
16.708.404.814.0013.606.844.113.47
16.438.284.703.9113.396.754.023.39
Good16.158.174.603.8213.176.663.933.31
 (e.g., cat. 3)15.888.054.503.7312.956.573.833.23
15.617.944.393.6412.746.483.743.14
15.347.824.293.5512.526.393.653.06
15.077.714.193.4712.316.303.562.98
14.797.594.083.3812.096.213.462.90
Moderate14.527.483.983.2911.886.123.372.82
 (e.g., cat. 4)14.257.363.883.2011.666.033.282.73
13.987.253.773.1111.455.943.192.65
13.717.133.673.0211.235.853.092.57
13.447.023.572.9311.015.763.002.49
13.166.903.462.8410.805.662.912.40
Fair12.896.793.362.7510.585.572.822.32
 (e.g., cat. 5)12.626.673.262.6610.375.482.722.24
12.356.563.152.5810.155.392.632.16
12.086.443.052.499.945.302.542.08
11.806.332.952.409.725.212.451.99
11.536.212.842.319.515.122.351.91
Untrained11.266.102.742.229.295.032.261.83
 (e.g., non-racer)10.995.992.642.139.074.942.171.75
10.725.872.532.048.864.852.071.67
10.445.762.431.958.644.761.981.58
10.175.642.331.868.434.671.891.50
As you will see my 2.85 put me between Fair and Moderate. Age adjusted increases this to the lower end of Good. Given that I am finishing in the middle of my age group on ironman distance bike legs, that seems about right.