What show was Michael J. Fox on while filming "Back to the Future"?

Michael J. Fox was starring as Alex P. Keaton on "Family Ties" throughout the entire "Back to the Future" shoot. Creator Gary David Goldberg agreed to let Fox take the movie role but with one non-negotiable condition: Fox couldn't miss a single day on the sitcom. This meant Fox worked at Paramount filming "Family Ties" from 10 a.m. to 6 p.m., then rushed across town to shoot "Back to the Future" until 2:30 in the morning. He kept this schedule going for three and a half months, surviving on just a few hours of sleep each night. Fox later admitted he got so exhausted he'd sometimes forget which set he was on and what character he was supposed to be playing. Both projects became huge successes, but Fox probably needed about six months of solid sleep to recover from the experience.