If you stride across a room like a young Travolta in “Saturday Night Fever,” your good posture will keep the muscles in your abdomen, back and pelvis (your “core”) strong and flexible — a big boost to staying injury-free when dancing like Travolta, jogging, golfing or biking. Need extra work on your core? Yoga will make you stronger and keep your joints younger.

But if you’re as wilted-looking as Napoleon Dynamite, you’re setting yourself up for weak muscles, arthritis, back pain, fatigue, headaches and even a potbelly.

Luckily, you can roll back your body’s RealAge if you trade in your slouch ‘n’ pouch for the virtues of vertical. Here’s how we You Docs do it:

1. Hold your head up straight; don’t jut out your chin; back it up a bit.

2. Keep your shoulder blades back.

3. Stretch the top of your head toward the ceiling. Tuck your stomach in.

4. Keep your knees straight when standing. Seated? No twisting, leg crossing or foot swinging. Plant your feet on the floor, knees bent at a right angle and even or slightly higher than your hips.

5. Standing: Put your hands on your hips. Don’t sling your hip bones or pelvis forward or backward. Seated: No need for a board down your back. Let your lower back curve naturally but don’t collapse on one hip.

Good posture gives you confidence and makes a great first impression. Both give you an edge, personally and professionally.

The You Docs — Mehmet Oz, host of “The Dr. Oz Show” and Mike Roizen of Cleveland Clinic — are authors of “YOU: Losing Weight.” To submit questions, go to www.RealAge.com. A King Features syndicate.