A 47-year Swedish study published in 2026 can tell us when fitness and strength begin declining — and I’m very surprised.

The study followed adults for almost five decades to uncover when physical decline truly begins. They looked at fitness, strength and muscle endurance, and how this evolves in adulthood. Here’s everything you need to know about the mammoth study and what age your physical fitness really starts to fade out (plus, how to fix it).

What is the study?

I came across the study in Science Daily, but it was conducted at the Karolinska Institutet. Researchers followed people for almost 50 years to assess how physical performance evolves as we age, and the results were surprising — to me, at least.