Good exercise plan for a middle-aged person who is out of shape (assuming good health other than the lack of fitness)

‘It’s a movable feast’’ in terms of workout options, says Dr. Michael Joyner, a physiologist at the Mayo Clinic in Rochester, Minn.

Pedal or swim if you have a bike or gym membership. But walking is, physiologically and logistically, the simplest exercise, Dr. Joyner says. Just put on comfortable sneakers — they don’t need to be new or expensive — and set off. Try to walk for half an hour.

‘‘Thirty minutes of moderately vigorous physical activity most days is really the sweet spot in terms of time versus benefit, from an epidemiological perspective,’’ Dr. Joyner says. ‘‘Moderately vigorous’’ means that your heart pumps at 50 to 70 percent of its maximum rate (which is, broadly, 220 minus your age for men, and slightly less for women) or, less exactly, a pace at which you can talk to a companion but you’re puffing too much to sing.

These 30 minutes do not need to be completed in one chunk, either. It is fine to break up the exercise during the day “into smaller bites,’’ Dr. Joyner says. And in fact, for certain groups of people, it’s probably more effective to do so. In one 2012 study, adults at high risk of developing hypertension improved their blood pressure more effectively if they walked for 10 minutes briskly three times a day than if they walked briskly once a day for half an hour.

‘‘Strength training is also a key,’’ Dr. Joyner says, ‘‘especially in late middle age. And it likely helps prevent frailty as we get older.’’ Many gyms have weight-training orientation classes.

Or just do push-ups and squats in your living room. Start with one push-up, if that’s all that you can do, and progress to 15 or 20.