Here's the age when strength and fitness begin fading, long-term data shows

Physical decline does not wait for old age. 

A new study tracked the same people for nearly half a century, finding that measurable drops in fitness and strength begin at around age 35 and continue gradually through midlife.

The study is based on the Swedish "Physical Activity and Fitness" cohort, which began in 1971 with participants born in 1958. Researchers enrolled 427 people, a mix of men and women, and tested the same individuals repeatedly over a 47-year span, according to a press release.