Originally Posted by
canklecat
The high rpm technique evolved to be more efficient for pros riding multi-day stage races with little time to recover. It wasn't common in an earlier era of bigger guys like Merckx, Indurain and others who didn't fit the currently vogue stringbean body type.
The only reason that guys in the distant past rode such low cadences on climbs was because sensibly long derailleur cages were unfashionable among racers. On a tailwinded shallow descent with someone pushing the pace, those guys would spin extremely high cadences as they topped out their gears.
For his hour record, Eddy Merckx chose 52-14 and averaged about 104rpm. He wasn't a low-cadence masher.