When Billie Jean King was growing up, her mother always told her, “Billie, you have to keep moving or it’s over.”

The tennis champion and social rights advocate, now 70, still champions that message, encouraging seniors to stay active so they can maintain independence as they age.

“I try not to let more than two days go by” without exercising, she says.

That’s not always easy for someone who travels so much. King aims for at least 15 minutes on a treadmill and 30 or 40 minutes on a stationary bicycle, including some sprints, most days. She also does exercises to strengthen her core and improve balance.

King, whose mother passed away in February at age 91, was in Austin this week to speak about fitness to residents of Atria at the Arboretum, a senior living community, and attend an event for the Andy Roddick Foundation.

King won 39 Grand Slam singles, doubles and mixed doubles tennis titles during her career but is perhaps best remembered for beating Bobby Riggs in the Battle of the Sexes tennis match in 1973. (He was 55, she was 29.) A champion for social equality and justice, she now serves on the boards of the Women’s Sports Foundation, the Andy Roddick Foundation and the Elton John AIDS Foundation.

“I think the most important thing is to admit what is — and I’m 70 now,” she says.

Her tips for other seniors? Modify exercises so they work for you.

“Even if it’s not 100 percent — find a way to do what you can do,” she says. Even exercises done while sitting in a chair are beneficial because they get your blood circulating. “Everyone has to decide what works for them.”

King, who has a hernia and a bad foot, says she’s had to adapt her routine. “We lose so much muscle mass as we get older,” she says. She’s also had eight knee replacements and a shoulder surgery — the result not of a tennis injury but of helping someone lift a bag into the overhead bin on an airplane.

“If I’m doing weights, I stand on one foot,” she says. “Anything that makes me have to pay attention. As we get older our inner ears are not as healthy, and that creates a challenge with balance.”

Another suggestion? Find an activity you like that doesn’t feel like a chore — like dancing.

As for diet, King says it’s harder to maintain a healthy weight with age. She’s trying to lose 20 pounds. She spent a year as a vegetarian but now varies from that diet occasionally.

“I’m a big believer in fish once in a while, and I will have red meat maybe once a year,” she says. “I don’t eat much at night, and I cut back on carbs.”

And she keeps moving.