humlan, after knee surgeries, I've been in a position that I couldn't finish a full cycle on a stationary bike too. Here's what the physical therapost had me do.

You rock back and forth with the pedal as far as you can in each direction, and do it over and over again. You will eventually be able to fgo all the way around. It's important to make sure the bike size is appropriate. The seat should be in the right place for your height. IF you are having a hard time doing a full cycle, you might be able to raise the seat so the whole way around is a shorter distance. Does that make sense? If not, ask questions.
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