Here's NFL running back Chris Johnson working out SO DAMN HARD at an L.A. gym Monday, he went and dry-heaved in the parking lot ... and TMZ Sports has the video. 

Johnson was haulin' kettlebells outside of the Unbreakable Performance Gym in West Hollywood -- where trainers pushed him to the brink of hurl city. 

Now, we never saw Johnson actually blow chunks ... but he was close ... and eventually got back to the weights to finish his workout like the monster that he is.  

Fun Fact -- Unbreakable is same place where Diddy raced (and BEAT) NFL star Dashon Goldson in an uphill sprint last month!