on the rivet [definition]
Extreme physical exertion to the point of almost giving up. Derived from bike racing in the olden days when bike seats had rivets, and in an effort not to get dropped one would slide forward on the saddle to exert maximum pressure on the pedals so as to hang on the the amphetamine-loaded Belgian in front of you.

https://www.urbandictionary.com/defi...%20the%20rivet