Testing will give you your anaerobic threshold, a good indication of aerobic fitness and,if you have a way of measuring, your power at threshold. You can then track if you are improving and by how much. As well, workout intensities are based your actual fitness rather than a theoretical percentage.
While there are a number of testing protocols for the cyclist, I prefer to use the "Carmichael Field Test" for its simplicity and ability to do it in the real world. This is 2 eight minute time trials with 5 minutes recovery between them. You can do this test outdoors, doing it on the same course each time, or on an indoor trainer. If you have an indoor trainer with enough resistance then this would be your best option as all of the variables such as wind and temperature are taken out of the equation. If done on a trainer make sure that the resistance is set the same each time to give an accurate comparison of fitness changes.
To do the test you will need a heart rate monitor that has a lap function and will give you average heart rate and total time for the lap and a bike computer that will give average speed and distance. Most bike computers don't have a lap function so you will have to reset your computer at the beginning of each test. As well it is helpful to have someone help with recording your information and hold your bike up so you can start with your feet in the pedals.
If you do the test outdoors find a loop course that is relatively flat. A paved running track at the local high school is ideal. Make a note of weather and wind conditions as this will have an effect on average speed.
Warm up for 20 minutes with three 30 second hard efforts to activate the lactate system.
Then from a standing start (clipped in with someone holding you up like a time trial) go as hard and as far as you can in 8 minutes. Get up to speed over the first 30 seconds and then try to hold the highest average speed you can.
Hit the lap button after the 8 minutes and ride easy for 5 minutes. Call out to your helper your average heart rate for the interval, average speed and the distance covered.
After your 5 minute recovery, get set and do it again. After the interval, record your average heart rate for the interval, average speed and the distance covered.
Ride easy to cool down for 10-15 minutes.
As you get fitter you will be able to go further during each test as well as be able to do the tests with a higher average heart rate. In addition to tracking your progress the test is important in setting your training zones. The higher average heart rate you can sustain leads to all of your training zone bumping up.
If you use a Powertap, then when you download your file you will see your two time trials very easily when you look a the graph of that workout. Highlight the first time trial and look to see the average wattage and heart rate. Do the same with the second, jotting the numbers down.
Now comes the math.
Functional threshold heart rate and power
Add the average heart rate of each test and divide by 2. Take this number and times it by.95. For training purposes, this will be within a couple of beats of your anaerobic threshold.
Add the wattage from the first and second test and divide by 2. Take this number and multiply it by.9. This will give you your functional threshold power.
Example: Test 1 Average HR 172 bpm - Test 2 Average HR 169
182+169/2=170.5
Anaerobic Threshold 170.5*.95=162 bpm
Aerobic Training Zone
To train your aerobic system you have to train below your anaerobic threshold. By knowing your threshold your aerobic training zone can be accurately calculated. Training at the right intensity will give the quickest results.
Take the Anaerobic Threshold and multiply by.9 to get the top end of your aerobic zone and multiply by.8 to get the lower end.
Example: Topend of aerobic zone 170.5*.9=154
Lowend of aerobic zone 170.5*.8=136
Typically, training zones have been based on a percentage of your max heart rate but this is difficult and painful to accurately figure out. Basing training zones on functional threshold will yield much better results as your threshold will change with training so your zones will change with it.