Originally Posted by
babyboomer
Perhaps it would help to clarify things if I explained my concern. Specifically, I'm concerned about the adverse effects of overtraining.
If my power meter is consistently under reporting my level of effort, it means that I'm consistently overshooting the target. I am far from an expert in these matters, but my guess is that the cumulative effect of constantly overreaching will interfere with my body's ability to adapt. So, for example, if I'm doing a workout consisting of several intervals at 130% of my 200 W FTP, but I'm actually doing 340 watts instead of 260, I don't think that's necessarily reason to rejoice. More likely than not, I won't finish the workout. In fact, looking back at the last six months, there are a number of the tough workouts that I did not finish. There could be any number of reasons for that, including the possibility that I'm just a wuss, but I'm just sayin'.
You're absolutely right and your concern is very valid. That would basically be a different workout than the one you intend to do and not a good way to train at all. Now, the most important thing is consistency. You've determined that the two methods give you different values, different by a wide margin. Using both interchangeably is simply not an option. You need to pick one and base all your training on it. If you have reason to believe your unit is defective, then by all means call Stages and see what they have to say. But honestly I doubt that will be the case, I think it is more likely that the virtual power is being over-estimated. I could, of course, be wrong. What trainer do you use?
My advise would be to use your power meter and forget about the virtual power. Do an FTP test with the Stages and base all your training on the numbers you get from the Stages, not from numbers you get from anywhere else.