No power meter? Just use your home trainer!

While we wait for better and cheaper power meters to come on the market, what options do we have?  Ed has kindly demonstrated that the Sporttracks Power Analysis plug-in may actually be pretty accurate. Plus or minus 3%, wow!

Another way of quantifying power output and "getting a feel" for the numbers is to use a fluid trainer. 

The resistance in a fluid trainer is a function simply of speed; the faster you go, the more the resistance you get.  Magnetic trainers on the other hand use a variable resistance to provide adjustable resistance.  An advantage of this is that resistance can be programmed, so that you can simulate the ups and downs of your favourite ride, with video cues as well, turning it into a virtual reality trainer, such as those made by Tacx and Computrainer. 

The main disadvantage with magnetic trainers is that they don't really feel like riding on the road, which is why I like my CycleOps Fluid2 fluid trainer.  Turning the drum on this trainer with your rear wheel forces an impeller to turn in a sealed drum full of silicone liquid.  This, coupled with a flywheel, somehow manages to give somewhat of an acceleration and inertial feel of the open road. 

It turns out that fluid trainers have a fixed relationship between power and speed. Some manufacturers actually publish a curve, like this one for the Fluid2:

One company, Kurt Kinetic, actually makes a "Power Computer" which, if it actually measured power, would be by far the cheapest on the market, at USD $79.99.  Unfortunately, all it does is convert the speed signal to a power number based on the characteristic curve for their trainer unit.   Kurt Kinetic has even gone trough the trouble of determining characteristic curve equations for competing trainers, so you can use their computer with those.  Unfortunately, the equation they provide for the Fluid2 looks nothing like the curve above, leading me to believe that they must have used a much older unit.

Unfortunately, the nice folks at Saris, the maker of the Fluid2, haven't published a table or an equation that would allow me to easily determine my power given my speed on the trainer.  Perhaps this is because they would rather you buy their $2000 Powertap powermeter? Anyhow, I picked a few numbers off the graph above and put the numbers in an Excel Spreadsheet to find that the curve is very nicely modeled by a third-order polynomial equation.  This one:

y = 0.0115x³ - 0.0137x² + 8.9788x

Where "y" is Power, and "x" is speed in MPH.

Adding a column for speed in KPH yields the following:

	x	y
Speed	Speed	Power
kph	mph	W
0	0	0
1	0.6	6
2	1.2	11
3	1.9	17
4	2.5	22
5	3.1	28
6	3.7	34
7	4.3	40
8	5.0	46
9	5.6	52
10	6.2	58
11	6.8	64
12	7.5	71
13	8.1	78
14	8.7	85
15	9.3	92
16	9.9	99
17	10.6	107
18	11.2	115
19	11.8	123
20	12.4	132
21	13.0	140
22	13.7	150
23	14.3	159
24	14.9	169
25	15.5	179
26	16.2	190
27	16.8	201
28	17.4	213
29	18.0	225
30	18.6	237
31	19.3	250
32	19.9	264
33	20.5	278
34	21.1	292
35	21.7	307
36	22.4	323
37	23.0	339
38	23.6	356
39	24.2	373
40	24.9	391
41	25.5	410
42	26.1	429
43	26.7	449
44	27.3	470
45	28.0	492
46	28.6	514
47	29.2	537
48	29.8	561
49	30.4	585
50	31.1	611

And now I can "train with power" on my home trainer, without a power meter, as long as I move my speed sensor to my rear wheel.

SportTracks "Training Load" Plug-In Primer

My new Garmin 310XT has taken over my life!!! Actually, I've been obsessing over the thing over the past few days and thought it may be of some value to pass on the results of my research...

My friend Justin suggested I look at Sporttracks. This program is an incredibly powerful way of unlocking many of the things Garmin watches can do, without the limitations of Garmin Connect, Garmin's online program.

Sporttracks is reasonably priced payware that enables you to download your activities from the Garmin into a logbook where you can monitor where you went and see all the data at all the points that you were at (things like heart rate, speed, etc.).

Unlike Garmin Connect, you can easily edit workouts, data points, and check total data for laps, sections of laps, or any part of any workout you'd like.

Given SportTracks licensing model, a community of users and developers has formed. As a result, there are a plethora of very useful add-ons, called plug-ins. These enable you to, among other things:

- download from the nearest weather station the weather for your ride or run;
- calculate headwind and tailwind for any point on your ride/run;
- analyze power for your ride/run;
- correct the elevation, using known elevation of points on the earth (GPS in general is only accurate +/- 10m, apparently I was surfing 12m waves whilst paddling in an outrigger canoe last week!);
- transfer all this data to workout websites, like RunSaturday.com, where you can analyze it further, and share it with others;
- upload data from other devices, like Polar's high-end heart rate monitor models; and
- import and export historical data from spreadsheets, so you can transfer all of that historical data from months and years ago.

The most fascinating plug-in for me is one called Training Load. It's very similar to a program called Training Peaks WKO+ Training Manager. This thing can act as a virtual coach, and with a little research can tell you how your fitness is improving, if you are training too much or too little, when to start tapering for a big event, and how to manage your fitness and rest to ensure you get there on a peak. It does this by applying known rates of change of fatigue, fitness, and performance based on one's training load - i.e. the stress that you subject your body to that improves your fitness - and the rest you take during which your fitness may decay whilst your fatigue decreases.

Training Peaks Training Manager is designed for cyclists, and it uses power data to determine a daily training stress score (TSS), which is just basically a way of quantifying how much a particular workout can contribute to your overall fitness. Some disadvantages of using Traning Peaks Training Manager include the fact that it is expensive, and it is for cycling only, so of limited use if you are a multi-sport athlete. You also need a power meter to use it. Power meters these days are very expensive ($1000 USD and up), and somewhat heavy, though a number of companies are promising lighter and better power-monitoring units for 2010).

The training stress score in the Training Load plug-in of Sporttracks uses only heart rate data, not power, so you don't need a power-meter, and it's results are valid for just about all endurance sports (though it takes a bit of effort to make it work for swimming, since nobody has figured out how to collect heart rate data under water). From the time you spend in different heart rate zones (all configurable in Sporttracks), it calculates a Training Impulse, or TRIMP. TRIMP basically determines a value for workout stress based on the time you spend in each zone, and gives you more credit for time spent in the harder, higher zones. Apparently, there is much research that shows that the use of TRIMP to determine training stress is quite valid, but very little to show that power does, so the results that you'd get from the Training Loads plug-in are perhaps even better than those you'd get from Training Peaks Training Manager.

There are a few good blogs out there that show the power of this plug-in in action, like this, this, and this.

However, it's not the easiest thing to use, as there is no manual, and all the information from the developer is posted in the form of a user forum, which takes a while to get through. Also, the flexibility of Sporttracks gives it somewhat of a lack of user-friendliness, though you quickly get used to its quirkiness after a few uses (meaning, after a few intimate late night sessions with the computer!).

In posts to come I plan on explaining some of the basic features of Training Manager in the form of a primer. I'll also explain how you can use Sporttracks to pump some of that data out to sharing web sites, like RunSaturday.com, and show how it can simplify the analysis of all that data.

In the meantime, here's my latest Training Load Chart (click image for larger):

The gold bars show my Training Stress Score for each day, with the column breaks giving me an idea of how much time I spent in each of heart rate zones 1-5. The jagged red line gives me an idea of my acute, or short term training stress. The blue area chart show my improving fitness level up to today (December 5th), and predicts how my fitness will decay if I do no exercise thereafter. The greyish-green area chart shows how my Training Stress Balance (sometimes referred to as "form") is getting really low because I've been training so much, but also tells me that if I do nothing after today, it may hit zero in mid-December.

The red curved line is the influence line. It tells me that the training I do around Feb 01 to Mar 08 (where the bulge is) will have the most influence on my performance on a half-Ironman I hope to do on March 21st. The curve goes negative on March 11th, meaning that if I do a lot of training after that, it will only have a negative effect on my performance, so that is when I will start to taper.