The purpose of the lactate threshold test is to determine the point at which an athlete shifts from mostly aerobic energy production to mostly anaerobic energy production. For cycling events such as a time trial or shorter distance triathlon (under one hour), knowing your lactate threshold as measured in average watts is particularly important. Ideally, the athlete wants to build to the point of lactate threshold and hold it right there throughout the race - going a little above on the hills, recovering on the down hills and nailing it on the flats. Lactate threshold, also referred to as 60-minute Critical Power or CP-60 (per Friel) or functional threshold power (per Colgan), refers to the athlete's ability to sustain a pace for a one-hour period. Oh, and by the way, it hurts.
While lactate threshold can be estimated using a power meter (more on this in another entry), completing the lactate threshold test in a laboratory setting provides you with the best estimate of your actual threshold.
I completed a lactate threshold test at the OA Performance Center in Saco, ME in March 2009. The test takes about an hour, and I found it was helpful to have a general idea of where your threshold power might be. I estimated mine to be somewhere in the 250-280 watt range.
The lactate threshold test began with an easy warm-up below 200 watts. The performance specialist administering the test took a blood draw every 5 minutes and recorded the results. After a 15-minute warm-up, OA started turning up the watts, requiring me to pedal at 245 watts for 15 minutes at a cadence of 90 rpm. I had little trouble holding 245 watts, and my blood draws every five minutes at 2 mmol/L showed that I was removing lactic acid efficiently. Once I had completed 15-minutes at 245 watts, the performance specialist took it up a notch to 260 watts. My blood values rose rather quickly to 4.3 mmol/L and stabilized, even declining slightly towards the end of that 15-minute block. The lactate threshold test was showing that I was still using large aerobic energy production, but that more anaerobic work was also being done. Then, we went to 275 watts. The test quickly became difficult and my blood values continued to rise, first to 5.5 mmol/L, then to 7.7 mmol/L then to 8.8 mmol/L, and I labored to complete the test. Clearly, I had exceeded my lactate threshold during this block of the test.
After the test was completed, OA Performance Center staff provided me with a complete report of my results with the determination that my lactate threshold was 265 watts. Not bad given that it was mid-March. I still had time and room to improve prior to race season. My only regret is that I did not return later in the season to see by how much I had moved the needle by doing another lactate threshold test.