Wednesday, December 06, 2006

Thoughts on threshold measurement

I like data, so about a year ago, I had my lactate threshold professionally measured using a breathing apparatus that measures accumulation of lactate in your exhaled breath, which represents an accumulation of lactate in your bloodstream. In theory, lactate accumulation means that you have reached or exceeded the point where your body can clear lactic acid faster than it's being produced by the work of your muscles. A buildup of lactic acid eventually requires you to lower your power output (effort).

Two tests in winter 2005 indicated that my threshold, based on lactate accumulation, was at a heartrate of about 135 bpm. I hadn't been training much in fall 2005, but that seemed very low to me. I knew from hard training rides and training for triathlon that I could maintain a heartrate of 160 for an extended period, 20 or 30 minutes at least.

Over the past year I've done some bike racing and have determined purely through trial-and-error that my threshold is around 158-160 bpm. (I'm defining threshold here as the effort on the bike that I can sustain for a lengthy period, specifially, I'm using the Dr. Andrew Coggan definition of Functional Power Threshold (FTP). He says FTP is the max power that you can hold for 1 hour, which is a very practical definition as far as I am concerned.) I recently bought a power meter, and from last week's test, I know for a fact that my current FTP is 238 watts. I also know for a fact that my FTP heartrate is 160 bpm (it was very steady during my test).

I don't question whether my 2005 lactate threshold test actually reflected an increase in blood lactate concentration around 135 bpm. So that leads me to this conclusion: Be very careful about how you define threshold effort. It might be accurate to state that my lactate threshold is 135 bpm, but of what use is that information? I don't want to use that number to set up my training ranges, and it doesn't tell me how hard to ride in a breakaway. It's just the effort at which my blood chemistry starts changing.

I choose to define threshold as a number that is useful for me in training and racing. I think the Coggan FTP is most useful in that regard.