Reporter's notebook: My 24 hours locked inside a metabolic chamber

— -- ABC News' Mara Schiavocampo shared her experiences after spending 24 hours inside a metabolic chamber at Mount Sinai St. Luke’s Hospital in New York City. Schiavocampo's journey, which aired on "Good Morning America" today, was the first time that TV cameras were allowed to peek into a metabolic chamber, which is used to monitor your total energy expenditure and better understand how your body uses energy in everyday tasks such as resting, eating and exercising.

It was an offer I couldn’t refuse: The opportunity to spend 24 hours locked inside a metabolic chamber. Yes, I was actually excited about this.

First, some quick background. Five years ago I lost 90 pounds after having my daughter, a journey I wrote about in my weight-loss memoir "Thinspired." Then I got pregnant with my son and had to lose baby weight all over again. I’m proud to say I did it, losing a combined total of 130 pounds! Health and wellness is kinda my thing.

So when "Good Morning America" approached me about doing this story, it was a no-brainer. The chamber, at New York’s Mount Sinai St. Luke’s Hospital, measures oxygen consumption and carbon dioxide production to determine exactly how many calories you’re burning the entire time you’re inside. That includes while you’re sleeping, exercising or just hanging out. It can even tell if you’re burning carbohydrates or fat so that you can figure out the ideal fat-burning workout for your body. Pretty cool, huh?

Not so cool? Spending 24 hours inside the equivalent of a hospital prison cell. The 9-by-11-foot room is vacuum-sealed, which means once the doors shut, you’re in until the test is done. No human contact, period. Inside, there's a small desk, a futon, a mini fridge, a sink, a treadmill and, of course, a toilet. And keep in mind, it’s a hospital, so they're not exactly luxury accommodations. They suggested I bring my own sheets and blankets. I didn’t. I wish I had.

Space is tight. When I tried to do yoga, I kept kicking the wall behind me. The fridge was just a few feet from the toilet (ick). Every time I shimmied through the narrow passageway to squeeze onto the treadmill, I knocked something over.

We rigged the room with five GoPro cameras to record my every minute. When I needed privacy (i.e. a bathroom break), there was a very high-tech solution: I put a piece of black cloth over the lens. Having zero privacy was probably the most annoying part of the whole experience. I kept mentally reminding myself to be on good behavior. (“They’re watching you!”)

Periodically my producer or someone from the hospital came around to check on me. Even though they were inches away, we had to talk on the phone because we couldn't hear each other through the glass. Every five hours, they could pass me things I needed through a vacuum-sealed window. I was immediately lonely. And bored. I’d expected to enjoy the free time much more.

As it turned out, there wasn't much free time at all! I had a lot of work to do. I had to complete three different workouts so we could measure their effect on my body: yoga, a long run, and a high-intensity interval workout. As luck would have it, I didn't feel like working out that day, of all days. But that’s why I was there, so I dragged myself up and got it done.

I’d brought a bunch of books thinking this would be a mini getaway. It wasn't, and it wasn't exactly fun, but it was really cool. Best of all, it will teach me a lot about how my body works, a gift that’ll last a lot longer than 24 hours.