As OP mentioned "running". As someone who started running in his 30ies: Before you start running, learn warm up. And take it seriously. It's the most important

As OP mentioned "running". As someone who started running in his 30ies: Before you start running, learn warm up. And take it seriously. It's the most important part of running. Your knees in your 40ies will thank you for it. (My knees don't.)