This. There's no doubt that higher cadences have advantages, and that they're only achievable if one has a decent pedalling action, and the suggestions about rollers and fixed gears are good. But the OP referred to the "magical" 90 rpm, and there's nothing magical about any particular cadence. Different strokes for different folks. Ex runners with huge aerobic capacity but not much muscle mass will likely do well at high cadences because the CV system can take it and it eases the strain on the muscles. Those built like footballers might do better at lower cadences because lower cadences consume less oxygen for the same amount of power, and their limitation is likely to be their aerobic capacity rather than their muscular strength. So the OP shouldn't be misled into thinking there's a right number that can be prescribed. IMO the best training advice is to ride in a gear that is one lower than you feel you could comforatbaly manage. That will be different for everyone but will encourage a higher cadence and smooth action.