As people get older, their muscles don't send signals as quickly when they try to move, which might be why they lose strength over time.

When people of any age do strength exercises multiple times in a row, their muscles fire more intensely for a short while—and that’s when they get a quick boost in strength.

Older men who start out weaker or with smaller fast-twitch muscle fibers tend to get bigger gains from heavy weight training, but even knowing how weak they were at the start doesn’t fully explain why some people improve more than others.

Just because older people get stronger muscles doesn’t mean their legs get stronger — muscle size and leg strength don’t go hand in hand as we age.