My workout warm-ups are important, and not just for the role they play in getting the muscles moving. I do pretty much the same routine all the time, only occasionally making slight changes to my workout. By sticking to one standard, I can look at my performance during the warm-up and use it to tell me whether I should go easy or hard during the rest of the workout. If I am weak during the warm-up, perhaps it will be a good day to just take it easy. On the other hand, if my muscles are performing better during the warm-up, this might suggest that I have the energy to try harder workout.
Below, are the results from two of my workouts. You can see how the resistance (and also the RPM) increase over a number of steps during my 20 minute warm-up session. During my good warm-up, in the first graph, you can see that the average power on the hardest step of the warm-up was 26 W. In the not so good warm-up, in the second graph, the average power on the top step is only 19 W.