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Fitness Over 50

Louis Weintraub, who turned 100 in January, works out at a gym in Sacramento, Calif., on Feb. 21, 2014.

I recently had an “aha!” moment. At the end of December, I took two weeks off from teaching my classes (eight a week), mostly to give my older-than-57 knees a little break. I was still working out, but not as much and not at the level I am used to.

On the afternoon of the second day of not doing any physical exercise, I noticed something. I was feeling foggy and was having a hard time doing my job. I could not think straight. Something felt way off.