What's GOVSS?

Dr. Philip Friere Skiba

If someone asked you how much running you do, how would you respond? It is a more difficult question than it might appear. For instance, if you responded by saying, "Oh, I put in about 20 miles a week," you really didn't answer appropriately. Think about it. You ran 20 miles, but you didn't say how fast you went. 20 miles at 5 minutes per mile is a lot harder than 20 miles at a jog.

Ok, so you might say, "I put in about 20 miles at about 8 minutes per mile." Yet, even this statement does not tell the whole story. Is 8 minutes per mile fast for you? What percentage of your race pace does that translate into? Moreover, you really didn't just train at 8 minutes per mile, did you? You probably had a track workout as well, or one of your runs was faster because you were out with your training buddies. These details make important differences not only in communication, but also in your development as an athlete and your body's response to the training you do.

So really, how is it possible to take all of these variables into account? What we need is a training metric. A training metric is something that we can use to score a workout, which takes into account both the duration and intensity of the training. The first metric was something called the Training Impulse Score (TRIMPS), and was developed by Dr. Eric Banister back in the 1970's. It works by using heart rate, and follows the formula:

TRIMPS = Exercise duration (minutes) Average HR (BPM) A HR-dependant, intensity-based weighting factor

If you think about it, this formula makes good sense. We have duration (minutes trained), we have intensity (how high the HR is), and we also have this weighting factor, which you might initially be puzzled by. Here's the thing: Exercise difficulty does not increase linearly. In other words, running the 100M dash in 20 seconds is fine, but running it in 10 seconds is not just twice as hard, but many times harder. In other words, exercise difficulty rises exponentially. It curves upwards as you go faster, and the curve gets steeper the faster you go.

Dr. Banister developed this weighting factor by making a graph of heart rate vs. lactate concentration in the blood, because lactate curves upwards quickly as you run faster, indicating more metabolic stress on the body. Nice, right? So, we have this all figured out. We just use TRIMPS to tell us how much training we are doing.

Unfortunately, it isn't quite that simple.

It's like this: HR is not the best marker of exercise intensity. The reason is that HR is dependant upon lots of things that have nothing to do with how fast you are running. If you didn't get enough sleep last night, your heart rate might be off. If you are a bit dehydrated, it will run high. You get the idea. So this is kind of a bummer. It is like trying to use a ruler to measure something, but someone keeps changing the marks on the ruler.

It would be good if we had a marker for exercise intensity that had nothing to do with heart rate. Something easy to measure like speed, for instance. In theory, this is a great idea. GPS measures speed! No matter what your heart rate is, you can always tell how hard you are exercising by how fast you are going. However, this creates problems as well. Is an 8-minute mile on the flat just as hard as an 8-minute mile run up the side of a mountain? Of course not.

The difference between an 8-minute mile run on the flat and on a slope is one of power output. It takes more power to run the same speed going uphill, and you feel this by the sensation of increasing strain. In fact, your body responds to training stimulus based upon its actual work rate. Both scientists and cyclists have exploited this by putting power meters on bicycles. It is now possible to always know exactly how hard you are exercising. However, you can't strap a power meter to a person. Or can you?

You can actually calculate the power output of a runner utilizing a little math, and knowledge of the height and mass of the runner, the speed, the angle of the road, and the efficiency of the conversion of energy in the body to the outside world. GPS directly measures all the needed variables, so it is sort of like a power meter for your body.

So, we have established that we can calculate power output. Now we need to turn that into a points scale, and we need that scale to make sense. This is the easy part. Remember I told you that TRIMPS was weighted using blood lactate values? We do the same with this. Research has shown that lactate starts to rise significantly at the best pace / power output you can maintain for one hour, or about 10-15 kilometers, depending upon how fast you are. This is called the Lactate Threshold, and is the most important determinant of endurance exercise performance. So, it makes sense to try to use speed/power output at LT as the benchmark for exercise intensity.

Enter GOVSS. Using some complicated math, we set your best 1 hour power equal to 100 GOVSS. You can figure this out by doing a race that is longer than 10k, but not longer than 10 miles or so, and which takes about an hour to complete. Record the performance with your GPS, and load it into TopoFusion. Alternatively, you can enter your estimates of 1 hour pace and road angle into the program. The software does the math all by itself. Now, when you load your runs into Topofusion, you will get a number that allows you to compare runs to each other. A 75 GOVSS run is about 75% as stressful to your body as a 1-hour race. A 125 GOVSS run is 25% more stressful than a 1-hour race. You get the idea.

You can read a more complicated (but more scientifically accurate) explanation of GOVSS, and the mathematics involved, at http://www.physfarm.com





How to use the Run Analysis / GOVSS Dialog

Find the Run Analysis dialog under the "Analysis menu." In order to correctly calculate GOVSS and to keep your training log neat, you need to give Topofusion a few details.
Name, age and sex: Self-explanatory
Height and weight (actually, mass) are both critical for the algorithm, so it is important you get them exactly right. They need to be entered in metric units.

• Height: Figure out your height as a decimal value (e.g. 5.75 feet), and multiply by 0.3048 to obtain your height in meters.
  
• Weight: Take your weight in pounds and divide by 2.2 to obtain your mass in kilograms.
  

You then need to enter the details of your test effort. It should be 10k or greater, but should take one hour or less. It should also be run as hard as you can while still maintaining pace. Don't go out too hard and then end up walking or jogging.

• Test distance: This is really important, at least initially. Use your GPS to get this exactly right.
  
• Test slope: This is the slope of the road you are running on. If you are running on a flat road, this is not a problem. The chances of you running on a road of constant slope are slim, of course, but we left this for the sake of completeness. The average slope for the run would be sufficient.
  
• Time:The exact time for the test, in minutes and seconds.
• Please remember, this process will make 100 GOVSS equal to covering your test distance in the test time. If you want 100 GOVSS to equal 1 hour at race pace, you must make a guesstimate of what distance you might cover in 60 minutes using one of the many online calculators or books on the market (e.g. Jack Daniel's VDOT tables).

This will allow you to estimate your test power output, and calculate GOVSS with good reliability if you are not yet fit enough to complete an appropriate test effort. Once you are able to complete a good test effort and evaluate the run, you can change over and enter the resulting average power value in the "Calculated Average Power" box. This will allow a more exact power measurement and better calculation.

Other important details:

• Altitude correction: This button is critical. The GOVSS calculation is tied directly to how good the altitude readings from your GPS are. For various technical reasons you can read about elsewhere, GPS altitude data are notoriously unreliable. Fortunately, these data can be corrected by Topofusion. Just push the button.
  
• File to analyze: There can be a number of files in the window, depending upon how many you have selected. You should be sure to select the file you are actually interested in.
  

Provided you entered everything correctly, you'll get a bunch of data in the window on the right hand side of the dialog.

GOVSS: The workout score. Higher is indicative of more physiologic stress. 100 GOVSS is equal to your test effort at test power output.

• Lactate Adjusted Power: This is how the workout "feels" to your body, physiologically speaking, in comparison to a flat, evenly paced run at the average power calculated. For instance, if your run included a number of hills, this would be physiologically more taxing (provided you maintained pace), and would be reflected by a higher Lactate Adjusted Power. Basically, it is a weighted average, where power output above your test power is weighted progressively heavier to account for it's greater physiologic impact.
  
• Average Power: This is the exact average power output you generated. It should typically be a little bit lower than the Lactate Adjusted Power. If the file you analyzed is a maximal effort ~hour run, this is the number you would enter in the "Calculated Average Power" box.
  
• Kcal: This is not how many calories the workout burned. This is the actual external work you have generated. Depending on your own personal variables you probably burned at least 2x as many calories.