I have a good mate who was complaining the other day about not being able to go very fast and feeling sluggish. Someone noticed how low his cadence was and asked him what his computer was averaging it at. He said 71 rpm. What!? 71 rpm!? “Well, what should my cadence be then?”, he asked.
Let’s first assume that “optimal” means “most efficient aerobically”. Many different studies have been able to determine how much oxygen is used at different cadences with a resulting efficiency figure – the less oxygen used, the more efficient that pedal cadence is. Nearly all of the results for these studies, when plotted graphically, showed an ‘inverted U’ shape, with the extremely low and high pedal cadences being less efficient and an optimum figuring somewhere around the middle. There was a general consensus from these studies show the optimum was around 90 rpm.
The lower gear provided by a high cadence means that acceleration is relatively easy, so higher cadence is important in road races when you have to be ready at all times to follow the accelerations.
Also, remember a few posts ago where I talked about the glycogen stored in fast and slow twitch muscle fibers? Another reason why a high cadence is more economical.