Recovery and Training Stress

I think one of the biggest challenges for every cyclist is knowing when to train hard and when to take it easy.  Here is a good example of how monitoring heart rate and power for your hard workouts can indicate if you are rested enough to do the workout or if you need to take a break and come back the next day.  I did this workout on Saturday, 8/25/09:

For this workout, I did four intervals maintaining an average around 350 watts for each 18 minute interval (5 minute rest between intervals).  My heart rate averages were 168, 173, 176, 177 bpm.  The following day, I raced the HART criterium in Denver, CO.  On Monday, I rode easy for an hour, then on Tuesday I attempted the same 4x18min workout.  This time, however, I was not rested enough to do the workout and it was evident in my heart rate. 
 

My average heart rate for the first two intervals were 171bpm, then 180bpm.  I attempted a third interval, but was too tired to complete the effort.  My heart rate was much higher indicating I was stressed and not recovered enough to do the workout.  I use this data for planning my future workouts.  If I do two hard workouts or races in a row, then I will most often need two days of rest before I can do another hard workout.  Everyone is different though, and you may recover quicker or slower than others.  The best way to determine if you are rested (in my opinion), is to monitor heart rate with power.  I structure my training plan completely around power, but I monitor heart rate to see how I felt and as a gauge for fitness.