Run, mama, run. And tell me how you do it. (Julie Francoeur) Run, mama, run. And tell me how you do it. (Julie Francoeur/iStock)

After my first son was born, I was a winded wonder. My exercise routine consisted of doing laps around the house with a newborn in the Bjorn, trying to get him to sleep. I did mommy and me yoga, and loved the quiet time I had with my new guy and the companionship of others in similar circumstances. The zoo, with its big uphill climb, was a regular routine for me — but it usually included a stop for a treat on the way up.

And now that my boys are 6 and 4 years old, I consider a day of playing tag/baseball/walking to the playground decent exercise.

In other words, if anything, having kids, and the exhaustion that goes with it, has made me less willing or able to exercise.

But an article in Outside Magazine is asking if babies are the new Performance Enhancing Drug. Why? Because a few new moms have done incredible things. Like Liza Howard, who ran a 100-mile race in record time, and stopped to pump breast milk along the way. When her baby was about three months old, she did a 100K race, and the sleep-deprived mama stopped midway to take a nap, and went on to claim second place among the women runners. Others have accomplished similar post-partum feats, like Paula Radcliffe, who won the 2007 New York Marathon, and had a 10-month-old at the time.

For me, my babies did the opposite of making me want to exercise. I was, like most moms, exhausted. And if I had a free moment, I just wanted to sleep — not train for a marathon. For others, it seems babies may have heightened their already strong drive to exercise, run and win.

This all goes back to something I’ve wondered for a long time: How do some people have the energy for physical challenges like this, or for getting up for 6 a.m. exercise classes (which I’ve started and stopped and am trying to start doing again)? How do some have four kids and work and doing seemingly everything without breaking a sweat? Is it nurtured, or is it nature? And how can I get me some of that?

My old colleague and friend, Jennifer Baker Moore, is the mother of four kids and needs to do at least a half hour of cardio on the days when she’s not teaching some sort of intense exercise class. “I feel that if I exercise, I actually DO have more energy,” she wrote to me. Which is a funny notion, because I’ve never known her to not have energy. (In fact, colleagues started calling her “Hurricane” years ago, if that tells you what she’s made of.) That said, she mentioned she comes from a family of women who exercise frequently. One is a police officer, one is a marathoner, another has her black belt, and, well, you get the idea.

So in place of that, my push is coming from friends who push me to join them for that early class, or go to the gym with them during lunch. Another friend and I try to schedule nights to hit the sidewalks for late evening walks and talks. But to naturally want to do at least a half hour of cardio a day? Or would I ever decide to run a marathon while still breastfeeding? I just don’t think it’s in my makeup.

But I’ll say it here: I’m going to that 6 a.m. class tomorrow. But it’s not going to be easy.