Many cyclists this time of year despair when they do their first indoor cycling workout of the season as they find their familiar workouts suddenly become impossible to complete successfully. There is much in the way of theory to this phenomenon with the most common centering on the boredom and lack of motivation experienced indoors. In my 10+ years of experience with a power meter I’ve found that my power will vary depending on the rolling characteristics of the bike. I produce the highest readings with the little extra resistance produced by either a long, very gradual uphill or on the flats with worn out cyclocross tires. I produce lower power readings on a high speed TT or triathlon setup where wind is more of a factor and mechanical resistance is less of a factor. The lowest readings I get are on a “mag trainer.” The explanation I believe is in something called “micro-rests” or “nano-rests” during pedal revolution which can now be measured . On a mag trainer, there is no “rest” during the pedal stroke whereas on the road, we pedal with slight surges. To me the trainer feels like I have no momentum in the pedal stroke. An interesting thing happens after enough indoor training; you will actually adapt somewhat to the different requirements and your indoor power will seemingly rise.
I think this also explains why different people have different experience with loss of power indoors. Trainers vary greatly in the way they produce resistance. Computer controlled, electronic units like the CompuTrainer and Vector have the capability of replicating road feel by changing the resistance slightly at different parts of each pedal revolution.
Interestingly, mag trainers probably do a good job of simulating the feel of riding a cyclocross or mountain bike through grass or peanut butter mud. Maybe being forced inside due to darkness or crazy bad weather is not all bad in some cases.
What is your experience with indoor power?