Physiology testing to determine your VO2 max and other statistics is useful for three reasons: the data can be used to scientifically identify your training zones, it serves as a baseline to your fitness level and can be compared with future tests to determine any change in fitness level, and it's a great motivator if you're not happy with the findings.
The price of the XC Oregon June 2001 Race Camp I attended included physiology testing on a treadmill (with ski poles) and a dunking in a hydrostatic weighing tank for assessing body composition (e.g., calculating the percentage of body fat). The testing took place at the Central Oregon Community College Physiology Testing Center.
The body composition test consists of striping down to a swim suit, stepping into a tank of warm water (hydrostatic weighing tank), kneeling on all fours, then exhaling as much air as possible while submerged under the water. That's the easy part. The hard part is staying that way - under water, no breath - until the computer completed its measurement. Only a few seconds, it seemed an eternity. Your normal body responds as if you're suffocating - as indeed you are! Panic sets in, you're about to leap up when the knock comes on the outside of the tank telling you the measurement is done and "You can come up now."
Then you do it two more times, each time trying to exhale even more air before submerging.
The next day was treadmill day. The first step was a second body composition test using skin calipers. Next, dressed in running clothes, you step onto a very wide tread, and are fitted with a heart monitor and a mask that connects to a machine that measures oxygen consumption. Next, they jab your index finger with a HUGE needle and take blood. This blood is used for a baseline lactate level. The hole that's left is big enough so they can continue to squeeze out blood every three minutes for the duration of the test.
After testing to insure the fit of the mask, you're given ski poles. The poles are taped at the end to cover the points.
Finally, the instructions:
Then the test starts. You begin ski walking at first, then bound as the speed and inclines increases. Every three minutes, they take a heart rate reading, squeeze for blood, then either increase the speed or the incline. At the end of 21 minutes, I'd had enough. Sweat's dripping in my eyes. My mouth is numb from the tightness of oxygen mask. My heart is ready to come out of my chest. I'm in pain... "Do you want to go another three minutes?" No! I'm done. I stand around for 4 minutes, then have blood drawn one last time to measure post-exercise recovery lactate level.
After going outside and running around the track a couple times to cool down, I come back in to get a briefing. Here's my results at age 43 and weighing 158 lbs:
The next step was to determine training zones. Four zones were determined from a graph of the test results (see the graph above). Zone 1 is the the heart range used for developing aerobic capability. Zone 2 is to be avoided - it's not very effective in developing aerobic capability and not fast enough to develop speed. It simply trains one to ski at a medium pace. Zone 3 is around the anaerobic threshold and increases the pain threshold. Zone 4 is for speed training while peaking.
The first step is to find the anaerobic threshold. The anaerobic threshold was determined by finding where lactate levels and true O2 lines cross in the graph. Zone 3 is defined as the range between two beats above and below the anaerobic threshold. Zone 4 is from Zone 3 to the max heart rate. Zone 2 starts 20 beats below Zone 3, and Zone 1 starts at the point where I actually have some ventilation going, up to Zone 2. (Apologies if I didn't listen close enough and misrepresent the Physiology Testing Center staff explanations.) So how does that translate?