I’m going to make a blanket statement here, which I rarely do: this is not true.
Sure, maybe you’re not going to run a marathon tomorrow, but, can you walk?
Walking for 20 minutes per day counts as exercise. Also, it’s one of the commonalities shared by centenarians in the Blue Zones. (People who live to be over 100 years old.)
If you can’t walk, and you’re bedridden, you can lift up your arms and legs and make small motions of some sort. You can start somewhere, no matter how small, with the help of a PT if needed.
Exercise does NOT mean ‘going to the gym’ … which is a phrase that I will branch another list about.
Move your body, well and often.
For some people, that’s gardening.
I’m a big fan of weightlifting. I have a garage gym.
But I don’t assume that everyone should pick up a barbell.