1970–1995 De Mars began her
judo career at the age of 12 at a local
YMCA. The same year, she entered college at
Washington University in St. Louis as a Business major. At the age of 18, as a college junior, De Mars was an exchange student at
Waseda University in Tokyo, Japan. While there, she trained under Sensei Osawa. She graduated from college with a degree in business in 1978. She also won the US Senior Nationals, US Collegiate Nationals and the US Open. In the absence of women's
judo world championships, she quit competitive judo and studied for an
MBA at the
University of Minnesota. which came in handy while teaching her daughter Ronda the proper mindset to take before fights. De Mars enjoyed more success in 1983, including the
Pan American Games and US Senior Nationals, and in 1984, winning the Austrian Open, Canada Cup (now known as the "Rendezvous"), and the US Senior Nationals. She came out of retirement to win the
1984 World Judo Championships, becoming the first person representing the United States to win a World Judo Championships (her name at the time was Ann-Maria Burns).
1995–present In 1995, De Mars' then-husband Ronald Rousey suffered a sledding accident which resulted in a broken back and chronic pain. Later, he was diagnosed with
Bernard–Soulier syndrome, which complicated his pre-existing injuries and he was given a prognosis of two years to live. He later committed suicide. Following this, De Mars moved her family back to
Southern California and settled in
Santa Monica, where she homeschooled her children. Following the move, De Mars remarried, and helped coach her daughter
Ronda Rousey, to win a gold medal at the 2004 World Junior Judo Championships and a bronze medal at the
2008 Olympics. Ronda is now a professional
mixed martial artist and a former
UFC Women's Bantamweight Champion. De Mars frequently coaches and spars at a gym in Los Angeles, where she can recall breaking her wrist the first time Ronda finished a throw against her: "I didn't really think I was going to go, you know, so I put my hand out and she caught me", De Mars said. De Mars would "always, always, always tell kids don't reach for the mat." In 2013, De Mars and
Jimmy Pedro Sr. co-wrote the instructional book
Winning on the Ground, published by Black Belt books. Her philosophy in judo argues for an offense-centered attack. ==Teaching and technology==