Margarita Emilia Martirena Cal was a Uruguayan sprinter from 1982 until 1992.
Martirena was the daughter of a grocer.
She studied at the Liceo Rubino.
She moved to Montevideo in 1985 to study medicine at the University of the Republic and to train in track. She began running for Sporting Club Uruguay in 1982 and then for Defensor Sporting after the two clubs merged in 1989. She also competed at the Ibero-American Championships in Athletics in Seville in 1990, and came in third in the 4x100 relay, breaking the Uruguayan all-time record in relay.
She also broke the all-time Uruguayan record in the 100 meter dash in Montevideo with a time of 11.7 seconds.
She competed in the Pan American Games in Indianapolis in 1987 and in Havana in 1991.