Alex Simmons said:What time periods are we using for the monod model? I have 1, 3, 5 & 20 min MMPs in there. I find this choice can vary AWC calcs considerably.
My recommendation is that people use data from tests >~3 min but <~30 min in duration. Here's why:
As you know, the critical power paradigm assumes a linear relationship between work and time, with the slope of this relationship representing one's critical power, i.e., a power that "...can be maintained for a very long time w/o fatiguing." In fact, critical power can, in theory, be maintained forever. Of course, no exercise intensity can be maintained forever (indeed, as I like to joke even resting metabolic rate can only be maintained for one's lifetime), which immediately reveals one of the limitations of this approach: the data don't really conform to a perfectly linear relationship, but instead will fall progressively further and further below the line-of-best-fit as the duration is extended. However, as long as you limit yourself to tests <~30 min in duration, you'll get a good fit to the data, and the calculated critical power will be highly reproducible (anaerobic work capacity somewhat less so). OTOH, if you include points beyond that time, you will tend to obtain a lower estimate of your critical power, and will tend to overestimate your anaerobic work capacity.
That explains the choice of the upper limit...what about at the short end of things? Again, the selection of 3 min is based on trying to minimize another limitation of the model, albeit one that isn't so intuitively obvious. Specifically, some inherent assumptions of the critical power paradigm are that 1) all of one's anaerobic work capacity will be fully expended during a particular effort (test), and 2) aerobic energy production is fully "online" from the very instant that exercise begins. In fact, neither of this is really true: it generally takes 1.5+ min to fully utilize all of your anaerobic work capacity, and VO2 won't reach a true steady-state until at least that long, and in fact usually longer. The consequence of these violations of the assumptions of the critical power model is that you can't do as much work in only a few minutes as the model predicts, such that those points, too, will tend to fall below the regression line. If you choose to include them anyway, you will obtain a higher estimate of your critical power, and a lower estimate of your anaerobic work capacity.
(BTW, after arriving at the conclusion that tests of the above duration were really best - despite the fact that tests of 1-10 min are routinely used in scientific studies - I subsequently came across a published paper that presented the same recommendation. Unfortunately, the literature on critical power is quite large, so I can't find the latter paper for you at the moment!)
