Workout programs are like 401(k)s — they need to be re-balanced over the decades.

“As we age, we need to gradually take out the risk and put in more ‘blue chip’ elements,” said fitness expert Tom Holland.

These four basic-yet-effective exercises — a squat, pushup, bicep curl and abdominal crunch — should remain in your program as long as you can perform them correctly, Holland said.

“When you’re young, blue chips are often perceived as being too easy, yet they are the key to creating and maintaining a strong foundation,” he said. “You may have to modify them slightly as you age — not going down as far on a squat, for example — but you keep them in as long as possible.”

As the body ages, it naturally begins to fall apart, with some functions breaking down faster than others. After age 20, the maximal amount of oxygen your body can use falls by 1 percent a year.

By the time you’ve hit 30, muscular strength begins to head south. But most of the decrease occurs after age 50, when it drops at the rate of 15 percent per decade. Bone mineral density also decreases with age; in women the rate accelerates after menopause.

What to do? Experts say the ideal combination of exercise for healthy aging should include aerobic, strengthening and flexibility exercises.

Balance exercises are also vital in helping prevent falls, which can lead to fractures. And though higher-intensity training programs are effective, less rigorous workouts can be just as effective, as long as they are done consistently.

Tweaking your workout can keep you active well into your golden years. Here’s how to reduce the risk in your exercise portfolio:

If you’re a runner:

Train like a triathlete because if you only run, you’ll be forced by injury to switch to swimming and biking to rehabilitate overuse injuries. Swimming is beneficial because “your posture and body weight is horizontal to gravity, so you work many muscles that receive little attention when running or can become weak and prone to injuries, such as the hamstrings, abdominals and low back,” said Michele Olson, a professor of exercise physiology at Auburn University in Alabama.

If you’re a swimmer:

Add gravity. Incorporate strength training, walking or anything weight-bearing to help prevent loss of bone density, said Pete McCall, of the American Council on Exercise. Also spend an equal amount of time on your back to help balance out the curves of the spine, recommends Jill Murphy, a strength and conditioning specialist in Neenah, Wis. Adding some backstroke into the mix “will stretch your pectoral muscles and work the muscles between your shoulder blades that help stabilize your spine and maintain your posture all day long,” she said.

If you’re a cyclist:

Run. “Cycling mainly involves the quadriceps muscles while running is primarily a hamstring activity,” Holland said. “When either of these muscles is too strong, injury occurs. Combining biking and running keeps these muscle groups balanced, which keeps you injury-free.” Also try a stationary rower, which doesn’t put vertical pressure on the knees, McCall said.

If you’re a bodybuilder:

Try yoga. “Improve your flexibility and provide a static challenge to the muscles vs. the dynamic ‘pump, pump, pump,’ rep after rep you’ve experienced with a long-term routine of bodybuilding,” Olson said.

If you’re a tennis player:

Balance the other side. “Do resistance training and in the form of dumbbells, bands and tubing to balance the strength on each side of the body,” Olson said. “If you are right-handed, most of the joints and muscles on the right side of the body will be better developed than those on the left side. With free weights, each arm has to independently hoist the weight such as shoulder presses with the left side vs. the right side.”

If you don’t work out:

Start moving. “Don’t worry about weights, just get up and walk or try something fun like Zumba,” McCall said. Start with a form of cardio, such as walking, spinning or using a cardio machine. Adopt a good core-building activity, such as Pilates, to build a baseline of strength. Holland recommends exercise DVDs. “They’re ridiculously inexpensive now, you don’t have to leave home to exercise and you can find everything from tai chi to P90X,” he said. “And if you press ‘play’ enough, they really work.”