But first, a tiny bit of personal background. As a kid, I was a sit-on-the-couch-and-read kind of girl. My mom was heavy, my family was not active, and I grew up in a community that celebrated events with large meals, not with hikes.

When I was 17, I decided I had to do something about this. I put on my little Tretorn sneakers and ran up the street. I was back in my living room about 3 minutes later, lying on the floor, hyperventilating.

So I had..let’s call it an uneasy relationship with fitness.

In my early adulthood, I was lucky to figure out that I could intentionally shape my own life. I was also lucky to have a bossy therapist who told me one day that I had to either commit to rigorous physical activity or see a psychiatrist about antidepressants. I chose the former, and I got myself to the gym 3 days a week.

I learned that physical activity would reliably turn a bad mood around, and I began to be pulled towards fitness by a carrot. I joined a running group and a cycling group. I loved being part of those communities, being outside, being fit. I ended up running 3 half-marathons, and after each one I gave an emotional high-five to that teenager lying on the floor, out of breath. It was a triumph over the past.

I’ve also been pushed towards fitness by a stick. I watched my dad rest at each landing as he climbed up the 3 very short flights of stairs to my condo in Boston. I witnessed my mom’s sad and chaotic decline from uncontrolled diabetes. After her first visit to the hospital, I began to work out every single day. I didn’t want my future to look like this.

I once heard the expression “there’s no zealot like a convert” and when it comes to fitness I have to admit: guilty as charged. (Yes, I *am* the one who shipped kettlebells to Baja for my month-long sabbatical session and then gave them to Chip. If you’ve stumbled upon them in the new movement center and used them: you’re welcome!)

There are a few things I know for sure, and this is one of them. Healthy aging requires us to move our bodies. You don’t get to be a kick-ass 90 year old without building muscle and pushing your cardiovascular system.

I have become a disciple of Peter Attia and his concept of the Centenarian Decathlon. Basically he says this: think about the activities you want to be able to do when you're 90, like climb stairs, get in and out of the car, pick up a grandchild. Then recognize that if those things require physical strength - and they all do - you need to start to train for them right now. Even if these are effortless today, if you don’t train for those activities, they’ll be taken away from you. And you don’t get a lot of warning, it just happens.

Fitness is not about the six-pack. It's not about fitting into your jeans. Fitness is about building and maintaining the ability to do fun things for our entire lives - travel, play with little kids on the floor - as well as do essential things like carry groceries into the house and walk your suitcase up 3 flights of stairs if the escalator in the airport is broken.

Personally, I want to be able to have a picnic in the park on a beautiful day, getting up and down from the ground easily. I want to be able to run to catch the train to Rome. And I want to put my suitcase in the overhead bin all by myself. (Step aside, gentlemen. I got it.) I also want to be able to carry stuff in from the car and to slip on the ice and not fall. And, if I do fall, to get up by myself with a bruise, not a fracture. What do you want to be able to do?

It’s an important question to ask yourself now. And then to train for it. Start now.

Alisa Cohn is an MEA alum, executive coach, the author of From Start-up to Grown-up, and the host of the podcast From Start-up to Grown-up. Thinkers50 named her top startup coach in the world. She guest lectures at Harvard, the Naval War College, and Henley Business School, and has been featured on the BBC World News, and in the NY Times and Wall Street Journal.