There was a time when exercise was easy.

As youngsters, most of us couldn’t wait to get outside and run around, maybe ride a bike or play ball.

Well, balls are back, even for older folks. There are big balls for strengthening and little balls for stretching, and both promise to inject fun into any exercise program. Whether you’re an experienced athlete or a newly reformed couch potato, a challenging ball workout can be tailored for you.

“It’s unbelievable the things you can do with this ball,” said Sara Hauber, a Hermosa Beach fitness trainer who specializes in stability-ball workouts. “It’s so comprehensive and it forces you to use your whole body when you work out.”

You’ve probably seen the stability ball — which looks like an oversized beach ball — at your local health club or sporting goods store. But you might not know that this large, air-filled orb is a great tool for a total-body workout. It can double as a weight bench or desk chair, and just sitting on it activates muscles in your back, chest and abdominals.

“You get strong from the center out,” said Hauber. “It improves balance and works the whole body.”

While most gyms have stability balls available for exercisers, “90 percent of people don’t know how to use them,” she said. “This is definitely something you need an instructor to do.”

The good news is that in about an hour, exercisers at any level can learn the necessary basics to incorporate the ball into their fitness routine. Many familiar exercises — from push-ups and sit-ups to bench presses — become even more intense when performed with the ball. In fact, simply sitting on the ball is an exercise. The “posture trainer” is among the first moves Hauber teaches clients.

“You want to have proper posture on the ball,” with shoulder blades back, stomach muscles pulled in and spine straight, she said. “You have to stabilize your core or else you’ll lose proper posture.”

One of the greatest benefits of working with the stability ball is strengthening the “core” muscles — those of the abdomen, chest and back. These muscles stabilize the body, creating a solid foundation for other physical activities. That’s why the American Council on Exercise recommends working with the stability ball to improve posture, balance and sports performance.

Avid exerciser Ricky Haas noticed an immediate difference when she worked with the stability ball for the first time.

“Instead of doing 50 million girly push-ups, I just do 10 and I can completely feel it all the way down my arms,” said Haas, 33. “I could feel the sit-ups in my butt, back and thighs. Every exercise felt like it was working three or four muscles.”

After all that hard work, a good, deep stretch is in order. Time for the 6-inch StretchBall. Smaller and a little softer than a soccer ball, the StretchBall helps with deep stretching and relaxation for all ages and fitness levels.

“Anyone can benefit,” said health and fitness expert Julie Feldman. “Anywhere you’re stiff, tight or achy, the ball is amazing. It’s like a deep-tissue massage.”

Feldman shows students how to roll their body on the ball to give overlooked muscles in the hips, shoulders and chest a much-needed stretch. You just lay there and the ball does all the work.

“It releases your back and your hips unlike anything else,” said Feldman, 32. “It really helps you relax. When I was super-stressed, it was my savior.”

Passive stretching with the ball stimulates circulation and can increase range of motion, Feldman said. She recommends a few minutes of daily StretchBall use and longer stretch sessions about once a week.

“You can stretch on the large (stability) ball but it’s more geared toward working out,” she said. “This is worlds apart from the big ball. This is for massage, relaxation and therapy.”

Feldman first learned about the StretchBall from her massage therapist in New York. Now she’s hoping to launch the trend in Los Angeles, teaching physical therapists, personal trainers, yoga instructors and fitness fans how to make stretching more effective and relaxing by using the StretchBall.

Avid runner Jerry Robinson, 58, found the StretchBall great for loosening up his legs.

“It really invigorates all the muscles,” he said. “It’s just fantastic.”

So the next time you’re seeking to boost your fitness program, you might want to play ball.