Amy Van Dyken -- Peddling a Stationary Bike ... ON HER OWN!

U.S. Olympic hero Amy Van Dyken is once again making huge progress -- she's moved from walking with the help of robotic legs ... to peddling a stationary bike all on her own.

The gold medal winning swimmer was unable to move her legs after severing her spinal cord in an ATV accident in Arizona back in June. In October, doctors equipped her with an Indego exoskeleton to help her walk.

But this week, Van Dyken posted a video on the stationary bike, with the caption, "At PT. Was making this bike move all ON MY OWN!! #progress #werk."

Pretty amazing.