The speed lab was created sometime after Barry changed the timeline again, this was one of the many changes that was made to the timeline. The treadmill was located in this room.
After Harrison Wells and Jesse Quick made their way to Earth One after discovering the latter gained superhuman speed, they were taken to the speed lab. Barry was surprised to learn such a room existed and Wells quickly deduced Barry changed the timeline, as he was unaware such a room existed either. When Jesse Quick tested her speed out in the lab, Wally left out of jealousy.
After several tests, Caitlin noted she could do good but was cut off, as Wells suggested they run more tests. When Jesse left the lab, Wells admitted he was stalling and told Caitlin and Cisco he brought her back to Earth One to get the team to talk her out of being a hero.