Maybe you’ve been running for twenty or thirty years, and you can feel it: the pace that once flowed effortlessly now takes a lot more out of you. Or maybe you’re lacing up for the very first time and wondering whether taking up running at 60 still makes any sense. Either way, you’re on well-charted ground. What actually shifts in your body from 60 on, how much weight those changes carry for your training, and what’s worth knowing already at 40 — science has clear answers.