Don’t hesitate! Get out and go for a run!Thinkstock

Everyone knows that tired old cliche, “You’re only as young as you feel.” Here’s an important update: “You’re only as young as you let your mind imagine.”

For those 50 and older: How many times have you made yourself hesitate, and then stop doing something you’ve done all your life? As an example, take someone we’ll call “Joe.”

All his life, Joe had walked up and down stairs using one foot, then the other. Just as he turned 59, Joe stumbled as he was walking down a flight of stairs. Instead of dismissing the near-fall as something that had occasionally happened before, Joe’s mind immediately began imagining that he was suddenly too old to balance on a flight of stairs. Instead of continuing to walk up and down stairs with youthful grace, he began placing one foot on a stair and bringing the other foot to it.

This extra protective method of using stairs had several negative effects. First, it was much slower and took more physical effort, so Joe began avoiding stairs. This caused his range of motion to decrease; because without stairs, his hip flexors and other muscles didn’t get used as much. So they began to contract and lose strength, as all major muscle groups do without regular use, regardless of age.

With his mind telling him that he was weaker and more feeble, Joe and his wife sold their two-story home and moved into a smaller ranch-style residence. But walking up and down stairs is exercise that improves balance and agility. Without this additional everyday exercise, Joe’s balance and movement skills began to deteriorate.

However, this story has a happy ending. One of the family’s friends was a physical therapist. When she saw Joe slowly and reluctantly dragging himself up the stairs outside her home; she began questioning him. Then she designed a therapy program that would eliminate the weaknesses and muscle imbalances that his mind had imagined were “just part of getting older.”

Here’s a scientific fact: Humans do not have to age as fast or dramatically as is commonly believed. Those who actually make an effort to stay active and mobile remain far more youthful than those who reach a certain age and gradually convince themselves that they can’t move around as much.

Perhaps your mind is telling you that you should be more feeble because of your age — only because this is the image that your mind has of your particular age. But the reality could be merely that you’re out of shape — which can happen at any age.

Start checking the reality of what your mind may be telling you about your limitations. Here are frequent lies the mind tells folks over 50:

• You’re “too old” to lose the 20 pounds you’d like to get rid of.

• You can’t go out alone to see a movie or eat at a restaurant because strangers will stare at you.

• People will laugh at you if you start working out at a gym.

Here’s the reality: You can always lose weight, just by cutting back on the amount and kind of food you consume. It may take longer after 50, but the pounds will gradually drop off. There are also a lot of older people who go out alone, even to fancy restaurants. No one will stare at you. And no one will laugh at you if you start going to a gym; you’d be surprised at how many seniors are now gym regulars.

Yes, getting older does require lifestyle changes. But before you make those changes, make sure they’re necessary: Measure reality against your imagination. Most important, train your mind to think about staying youthful, rather than fitting into some mental image of age.