Joined: Mar 2015
Posts: 1,106
Likes: 518
From: New Zealand
Bikes: Gunnar, Concorde, Peugeot 753, Marin, Pete Tansley, Rocky Mtn, Worldrider, Francis Quinlan, Bob Jackson, Winora, Avanti, Klein, Quintana Roo, Shogun, Carlton, Emmelle, Specialized
You need a pretty smooth pedal stroke to comfortably keep a high cadence.
The key is pedaling in circles, rather than jerky downstrokes and then ignoring the other 180°. Try unwieghting your leg or pulling up on the upstroke. It feels weird, but any movement feels weird until it enters muscle memory.
Your seat may also be too low.
Bouncing around on your saddle isn't a great idea for your balls or your knees or anything really.