I have this entirely mistaken idea that at some point in any workout you tip over from simply maintaining your fitness to building it. A twenty minute run stokes the fire. A forty minute run throws another log on. A two-hour run stacks the woodpile and opens the flue. The problem with this paradigm is that it’s not that simple, and more often than not it’s my legs that feel wood.

I sometimes come at this idea from a negative perspective, with a worse metaphor. My fitness is a balloon. A rest day lets some air out of the balloon. A short run reinflates it. A long run fills it to bursting. In this scenario, air is always leaking, and it makes me neurotic as hell. This one is a bit like the classic zombie nightmare, where you have to run to escape the zombies, but ultimately, it’s pointless, because the zombies will never stop, and you, well, at some point you have to.

I confessed this latter idea to Meghna during a recent run, and she said, “That’s a bad metaphor AND I think it’s wrong.” She did not call me crazy or stupid. Except with her eyes.

We had set out to do five slow miles, because it was Friday, and we were both tired and sore from the week’s work. As is our custom, we were running faster than we’d planned. This is usually but not always my fault. I had already taken a few turns on the trail that she had not cared for, thinking that we should head back to the car instead of veering off toward another stretch of work.

The route I was following takes in a series of short, sharp climbs that lead to water towers, or as I call them, the local Stonehenges. I didn’t share this information with Meghna, because I think most of the time it’s better not to know. It’s a gift just to run and not have to think too much. I’m sure she did not feel as though she had received a gift, but she was following me anyway.

As we wound down a wide gravelly road with just a quick right-hander to take us back to the car, I told her I was heading up the switchbacks to Stonehenge again, and she said she might not do that, but also that she might. And when I did finally take the sharp turn and start to climb the hill, I looked over my shoulder and there she was. Up and up we went, our breathing going ragged and our brains busy with the idea that this run might soon be over. And then we were down the other side and out and off the trail and walking up to the car.

And I said, “You know, I think, all metaphors aside, that there is this point in every run, where you’ve done enough, but that endurance comes from doing a bit more, pushing on a little farther or a little harder,” and she nodded and agreed. But still with that look in her eyes.