The B'aht Qul challenge was a Klingon ritual, similar to Terran arm wrestling, practiced to demonstrate physical strength. The challenge involves two opponents facing one another with their arms on a flat surface, such as a table. Then, they would lock their hands together with the backs of their hands touching. After a count, each competitor tried to push their opponent's hands onto the surface. He who did so first was declared the winner.
Captain Nu'Daq challenged Lieutenant Commander Data to the B'aht Qul challenge in 2369 after hearing of Data's reputation for great physical strength – Data easily won the challenge. (TNG: "The Chase")